Background
Primary neuroendocrine neoplasia (NEN) of the breast is a rare subtype of breast cancer
(BC) representing < 1% of all NENs, which occur most commonly in the gastrointestinal
tract and the lung [1], [2]. The prevalence of neuroendocrine differentiation among BC patients varies between
0.1 and 20% in the literature, with the World Health Organization (WHO) reporting
a prevalence of up to 5% of BC cases [3]. This discrepancy is due to the fact that the diagnostic criteria and definition
of this heterogeneous group of lesions have frequently changed in the last two decades,
and neuroendocrine immunohistochemical markers are not routinely used in BC diagnostics
[4]. The previous and current WHO classification of NEN of the breast are shown in [Table 1].
Table 1 Different classifications of NEN of the breast in the last two decades.
|
WHO 2003 [8]
|
WHO 2012 [9]
|
WHO 2019 [10]
|
|
* Expression of neuroendocrine markers > 50% (particularly chromogranin A and/or synaptophysin),
** no threshold for the expression of the neuroendocrine markers, 1 analogous to small-cell or large-cell lung cancer, 2 low grade tumors morphologically similar to carcinoid tumors of other sites. NST:
no special type.
|
|
Solid neuroendocrine carcinoma (NEC)*
|
Well differentiated neuroendocrine tumor (WD-NET)2
|
Neuroendocrine tumor (NET)
|
|
Invasive breast carcinoma with neuroendocrine differentiation**
-
special type
-
no special type
|
Invasive breast cancer with neuroendocrine differentiation overridden by morphological
tumor type should not be classified as a true neuroendocrine neoplasia but as a morphological
subtype (e.g., NST, mucinous, papillary) with neuroendocrine differentiation
|
|
Large cell neuroendocrine carcinoma (LCNEC)1
|
Large cell neuroendocrine carcinoma1 (LCNEC)
|
|
Small cell/oat cell carcinoma (SCNEC)1
|
Poorly differentiated neuroendocrine carcinoma (PD-NEC)/small cell carcinoma1
|
Small cell neuroendocrine carcinoma1 (SCNEC)
|
Neuroendocrine differentiation in BC was first described by Feyrter and Hartmann in
1963; this was followed by a series of eight patients with “primary carcinoid tumor
of the breast” reported by Cubilla and Woodruff in 1977 [5], [6]. Since then, many authors have tried to describe and characterize this heterogeneous
entity until in 2000, Sapino et al. proposed a definition for NEN of the breast as
a subset of tumors with specific morphological features and expression of the neuroendocrine
markers chromogranin and/or synaptophysin in more than 50% of tumor cells [7]. This definition was later adopted by the WHO classification of NEN of the breast
introduced in 2003 and last modified in 2019 [8], [9], [10].
While earlier classifications included a category comprising a subset of BC (no special
or special type, e.g., mucinous, papillary etc.) with neuroendocrine differentiation
as determined by morphological and immunohistochemical analysis, the latest version
excludes BC-NE from the NEN group altogether ([Table 1]). Through these changes, the WHO has attempted to develop a uniform classification
framework for NENs at different anatomical sites to provide pathologists and clinicians
with a consistent management strategy for NEN patients, since neuroendocrine differentiation
in BC, with the exception of small cell carcinoma, is assumed to have no therapeutic
significance [3].
However, there are certain diagnostic and therapeutic aspects of BC-NE that should
be acknowledged, even if current guidelines recommend treatment based on the general
principles of breast cancer therapy. The aims of this retrospective study were:
-
to analyze the clinical features and treatment strategies of BC-NE,
-
to assess the prognostic impact of BC-NE, and
-
to compare our results to previously published studies.
Materials and Methods
Patient material
A total of 27 patients with BC-NE treated at the Department of Obstetrics and Gynecology
of the University of Duesseldorf, Germany, between 2002 and 2013 were included in
this analysis. Surgically excised breast specimens from 465 BC patients treated between
2002 and 2006 were systematically re-evaluated in terms of neuroendocrine differentiation.
Moreover, a review of the clinical records of BC patients treated at our department
between 2007 and 2013 was performed to identify further BC-NE patients. Inclusion
criteria were: primary breast cancer with neuroendocrine differentiation (T1–T4, N0–3,
M0/M1) (TNM, 8th edition 2017) defined as > 50% positivity for the immunohistochemical
neuroendocrine markers chromogranin A and/or synaptophysin according to the NEN definition
from 2003 ([Table 1]). Exclusion criteria were the following entities: poorly differentiated large or
small cell neuroendocrine carcinoma and well differentiated
neuroendocrine tumor (NET, G1). The flow chart showing patient selection for
our analysis is presented in [Fig. 1]. The study was approved by the local Ethical Committee of the Heinrich Heine University
of Duesseldorf (Study number 4524).
Fig. 1 Flow chart of the selection process. Abbreviations: SYN: synaptophysin, CgA: chromogranin
A, BC-NE: invasive breast cancer with neuroendocrine differentiation, IHC: immunohistochemistry.
Immunohistochemistry staining
Tissue sections (2 µm) were deparaffinized and rehydrated. Endogenous peroxidase activity
was blocked with 0.3% hydrogen peroxide. Blocking non-specific protein-binding sites,
normal mouse serum was applied. Neuroendocrine markers were detected with specific
monoclonal mouse antibodies for synaptophysin (NCL-L-Synap 299, Novocastra, Berlin,
Germany) and chromogranin A (MAB 5268, Chemikon, Schwalbach, Germany) at a dilution
of 1 : 100 and 1 : 1000, respectively. Immunostaining was performed with anti-mouse
IgG and Vectastain ABC, followed by chromogen detection. Finally, the slides were
counterstained with hematoxylin and mounted for examination. SSTR 2A status was determined
with monoclonal rabbit antibody (UMB1, Abcam, Cambridge, UK) at a dilution of 1 : 50.
Membranous staining was scored as: 0: no staining; 1: weak staining (< 10%); 2+: moderate
staining (10 – 80%); and 3+: strong staining (> 80% tumor cells).
Statistical analysis
Statistical analysis was performed using SPSS (version 25). Survival intervals were
measured from the time of diagnosis until death or the first clinical, radiological
or pathological diagnosis of relapse, whichever occurred first. Relapse was defined
as either local recurrence or distant metastasis. Survival was calculated using the
Kaplan-Meier method. Primarily metastatic patients were excluded from the disease-free
survival (DFS) analysis.
Results
Patientsʼ characteristics
Clinical data from 27 patients with BC-NE were eligible for this study. Twenty-one
of these patients were identified by a systematic immunohistochemical re-evaluation
of 465 breast surgical specimens with regard to NE differentiation, resulting in a
prevalence of 4.5%. A further six patients were identified through an analysis of
the clinical records of BC patients treated between 2007 and 2013 and subsequent histological
re-evaluation ([Fig. 1]). Clinical features of the study cohort are presented in [Table 2]. The median age at the time of diagnosis was 61 years (range 38 – 84 years) and
22 out of 27 patients (82%) were postmenopausal. Nineteen patients (70%) had T2–4
tumors and 10 (37%) were node-positive with lymphatic vessel infiltration (L1) detected
in 8 out of 27 cases (30%). The most common immunohistochemical tumor subtype was
HR-positive/HER2-negative, diagnosed in 23 patients (85%), followed by
HR-positive/HER2-positive and triple-negative BC in two patients each (7%). Thirteen
tumors (48%) were positive for chromogranin A (CgA) and 25 (93%) were positive for
synaptophysin (Syn), whereas 12 tumors (44%) expressed both markers in > 50% of tumor
cells ([Fig. 2], [Table 3]). Somatostatin receptor type 2A (SSTR 2A) was analyzed in 24 tumors and of which
12 (50%) showed a SSTR 2A-positive status ([Fig. 3], [Table 3]). None of the patients in our cohort presented with specific clinical symptoms due
to neuroendocrine tumor differentiation.
Table 2 Clinicopathological features and administered therapy in the study cohort.
|
|
n (%)
|
|
* Initially diagnosed as NET G2. TNBC: triple negative breast cancer, BCS: breast
conserving surgery, NE: neuroendocrine, SSTR: somatostatin receptor, AT: anthracycline-taxane.
Numbers in parentheses are percentages and do not add to 100 in some instances owing
to rounding.
|
|
Total
|
27 (100)
|
|
Age at diagnosis
|
|
|
|
4 (15)
|
|
|
13 (48)
|
|
|
10 (37)
|
|
Menopausal status
|
|
|
|
5 (18.5)
|
|
|
22 (81.5)
|
|
Stage at diagnosis
|
|
|
|
6 (22)
|
|
|
14 (52)
|
|
|
3 (11)
|
|
|
3 (11)
|
|
|
1 (4)
|
|
Tumor stage
|
|
|
|
7 (26)
|
|
|
16 (60)
|
|
|
3 (11)
|
|
|
1 (4)
|
|
Tumor focality
|
|
|
|
21 (78)
|
|
|
5 (19)
|
|
|
1 (4)
|
|
DCIS component
|
|
|
|
12 (44
|
|
|
15 (56)
|
|
Nodal status
|
|
|
|
15 (56)
|
|
|
10 (37)
|
|
|
2 (7)
|
|
Lymphatic vessel infiltration
|
|
|
|
11 (41)
|
|
|
8 (30)
|
|
|
8 (30)
|
|
Original histology
|
|
|
|
16 (59)
|
|
|
1 (4)
|
|
|
1 (4)
|
|
|
4 (15)
|
|
|
5 (18)
|
|
Grading
|
|
|
|
21 (78)
|
|
|
6 (22)
|
|
Ki-67 index
|
|
|
|
6 (22)
|
|
|
8 (30)
|
|
|
11 (41)
|
|
|
2 (7)
|
|
IHC subtype
|
|
|
|
23 (85)
|
|
|
2 (7)
|
|
|
0 (0)
|
|
|
2 (7)
|
|
SSTR-based imaging performed
|
|
|
|
5 (19)
|
|
|
22 (81)
|
|
Surgical procedure
|
|
|
|
14 (52)
|
|
|
11 (41)
|
|
|
2 (7)
|
|
AT-based Chemotherapy
|
|
|
|
14 (52)
|
|
|
13 (48)
|
|
Endocrine therapy
|
|
|
|
24 (89)
|
|
|
3 (11)
|
|
NE-specific therapy
|
|
|
|
2 (7)
|
|
|
25 (93)
|
Fig. 2 Histopathology and expression of general neuroendocrine marker proteins in two different
breast carcinomas with neuroendocrine differentiation. a, d Hematoxylin and eosin (H. E.) staining demonstrates a solid growth pattern and complete
lack of tubular architecture in both carcinomas. Cytology of the tumor cells in a show an NST-like pattern, while cytology of the tumor cells in d is highly suggestive for a neuroendocrine phenotype. b, e Expression of the pan-neuroendocrine marker synaptophysin (SYN) in more than 50%
of tumor cells in b and in 100% of tumor cells in e. c, f Expression of the large dense core neuroendocrine vesicle marker chromogranin A (CgA)
in more than 50% of tumor cells in c, while tumor cells in f are positive in a minor subpopulation.
Table 3 Neuroendocrine-specific immunochemistry findings.
|
Marker/receptor
|
n (%)
|
|
NE: neuroendocrine, CgA: chromogranine A, Syn: synaptophysin, SSTR 2A: somatostatin
receptor type 2A. Numbers in parentheses are percentages and do not add to 100 in
some instances owing to rounding.
|
|
Total n (%)
|
27 (100)
|
|
Chromogranin A
|
|
|
|
13 (48)
|
|
|
4 (15)
|
|
|
10 (37)
|
|
Synaptophysin positivity
|
|
|
|
25 (93)
|
|
|
2 (7)
|
|
|
0 (0)
|
|
CgA and Syn in > 50% of tumor cells positive
|
|
|
|
12 (44)
|
|
|
15 (56)
|
|
SSTR 2A
|
|
|
|
12 (44)
|
|
|
2 (7)
|
|
|
7 (26)
|
|
|
3 (11)
|
|
|
3 (11)
|
Fig. 3 Expression of the nuclear transcription factor GATA and the somatostatin receptor
2A in breast carcinoma with neuroendocrine differentiation. a Hematoxylin and eosin (H. E.) staining reveals a solid growth pattern, complete lack
of tubular architecture and a cytology highly suggestive of neuroendocrine differentiation.
b Expression of the pan-neuroendocrine marker synaptophysin (SYN) in approximately
all tumor cells. c Nuclear expression of the breast-specific transcription factor GATA in the majority
of tumor cells. d Circular membranous staining for the somatostatin receptor type 2A (SSTR 2) in a
major subpopulation of tumor cells.
Clinical diagnosis and treatment
Standard thoracic and abdominal imaging (CT scan or ultrasound and X-ray according
to the current recommendations and internal standards) as well as bone scans were
performed in all patients at the time of diagnosis to exclude metastatic disease.
Additional SSTR-based neuroendocrine imaging (octreoscan or 68Ga-DOTATOC PET/CT) was performed in five patients with known neuroendocrine differentiation
of BC at the time of the diagnosis and a SSTR-positive score. Two primary metastatic
patients received an octreotide scan to confirm the NE differentiation of the metastatic
sites. In one patient with diffuse NE bone marrow infiltration and disease progress
after chemotherapy with epirubicin weekly and endocrine therapy with fulvestrant,
the octreotide scan was performed in order to evaluate the possibility of SSTR-specific
radionuclide therapy. This therapy was not administered as the patientʼs condition
worsened rapidly. In another primary metastatic patient
(bones, lung), NE differentiation of the metastatic sites was confirmed and SSTR-targeted
therapy with lanreotide was successfully administered for several months. Further
octreotide scans and 68Ga-DOTATOC PET/CT were performed during follow-up in this patient
to assess therapy response. Three other patients with unclear findings on conventional
radiologic imaging received an octreotide scan to exclude metastatic lesions with
NE differentiation.
Fourteen patients (52%) received a mastectomy, while breast conserving surgery was
performed in 11 patients (41%). Two patients had no surgical procedure, one because
of stage IV disease at the time of diagnosis and one due to her poor general condition
(advanced cardiovascular disease). Fourteen patients (52%) were treated with chemotherapy (5 patients received anthracyclines,
2 patients were given taxanes, 7 patients had anthracyclines + taxanes) and 24 (90%)
with endocrine therapy. Neuroendocrine-specific treatment with somatostatin analogues
was administered in two patients, one diagnosed in stage IV and one diagnosed in stage
II. The first patient with stage IV disease and metastases of the bone and lung (T3
N0 M1, G2, Ki-67 25%, HR+/HER2−, SSTR 2 + 70%) received endocrine therapy in combination
with lanreotide (120 mg s. c. q4w) after 6 doses of paclitaxel weekly 80 mg/m2 and achieved complete radiological remission with no evidence of disease at
the follow-up of 66 months. At least 60 cycles of lanreotide were administered
in combination with endocrine therapy until the last documented follow-up. No SSTR-analogue-specific
side effects which altered the therapy regimen were reported. The other patient received
the somatostatin analogue octreotide (2 × 50 µg s. c. per day) in stage II (T2 N1 M0,
G2, Ki-67 5%, HR+/HER2+, SSTR 2+), after standard therapy was considered unsuitable
due to the patientʼs poor general condition (cirrhosis of the liver (Childʼs C), thrombocytopenia).
Octreotide treatment was administered for 3 months, however this patient died 5 months
after diagnosis (no details regarding the exact cause of death or further symptoms
and side effects available). [Table 4] shows the systemic treatment of study patients according to tumor stage and receptor
status.
Table 4 Systemic treatment of study patients according to tumor stage and receptor status.
|
PT
|
Age
|
TNM
|
G
|
ER
|
PR
|
HER2
|
SSTR 2A score (%)
|
CT
|
ET
|
SSTR therapy
|
|
PT: patient, G: grading, ER: estrogen receptor, PR: progesterone receptor, SSTR 2A:
somatostatin receptor type 2A, CT: chemotherapy, ET: endocrine therapy, AI: aromatase
inhibitors, Ful: fulvestrant, E: epirubicin, Pac: paclitaxel, F: fluorouracil, C:
cyclophosphamide, DOC: docetaxel, A: doxorubicin, d: day, n. d.: not done, q1w: weekly,
q2w: every two weeks, q3w every three weeks, * no anti-HER2 therapy administered (PT
1 diagnosed in 2002, PT 27 not-suitable due to cirrhosis of the liver), ** no primary
surgery performed (PT 2: stage IV with malignant bone marrow infiltration, PT 8: not
suitable due to advanced cardiovascular disease).
|
|
1
|
61
|
T1 N0 M0
|
2
|
80%
|
80%
|
pos.*
|
2 (60)
|
No
|
AI
|
No
|
|
2
|
46
|
T4 N1 M1**
|
2
|
80%
|
40%
|
neg.
|
1 (< 10)
|
7 × E q1w
|
Ful
|
No
|
|
3
|
73
|
T2 N0 M0
|
2
|
80%
|
30%
|
neg.
|
0
|
No
|
AI
|
No
|
|
4
|
74
|
T2 N1 M0
|
2
|
40%
|
15%
|
neg.
|
0
|
3 × Pac q1w
|
AI
|
No
|
|
5
|
84
|
T2 N0 M0
|
2
|
90%
|
90%
|
neg.
|
2 (60)
|
No
|
AI
|
No
|
|
6
|
62
|
T3 N0 M1
|
2
|
80%
|
90%
|
neg.
|
3 (90)
|
6 × Pac q1w
|
AI
|
Lanreotide 120 mg q4w
|
|
7
|
53
|
T2 N1 M0
|
3
|
80%
|
0
|
neg.
|
1 (< 10)
|
3 × FEC – 3 × DOC
|
AI
|
No
|
|
8
|
72
|
Tx Nx M0**
|
2
|
90%
|
90%
|
neg.
|
2 (70)
|
No
|
AI
|
No
|
|
9
|
51
|
T1 N0 M0
|
2
|
50%
|
80%
|
neg.
|
0
|
No
|
AI
|
No
|
|
10
|
50
|
T2 N0 M0
|
2
|
80%
|
90%
|
neg.
|
3 (90)
|
6 × FEC q3w
|
Tam
|
No
|
|
11
|
42
|
T2 N3 M0
|
2
|
90%
|
90%
|
neg.
|
0
|
3 × A – 3 × C – 3 × Pac q2w
|
Tam + GnRH
|
No
|
|
12
|
38
|
T2 N0 M0
|
3
|
0
|
0
|
neg.
|
0
|
6 × FEC q3w
|
No
|
No
|
|
13
|
53
|
T2 N3 M1
|
2
|
0
|
0
|
neg.
|
n. d.
|
4 × EC – 4 × DOC
|
No
|
No
|
|
14
|
81
|
T4 Nx M0
|
2
|
90%
|
60%
|
neg.
|
3 (90)
|
No
|
AI
|
No
|
|
15
|
80
|
T2 N3 M0
|
2
|
80%
|
10%
|
neg.
|
0
|
no
|
AI
|
No
|
|
16
|
70
|
T1 N0 M0
|
2
|
80%
|
80%
|
neg.
|
0
|
No
|
Tam
|
No
|
|
17
|
56
|
T2 N0 M0
|
2
|
80%
|
80%
|
neg.
|
2 (60)
|
4 × EC q3w
|
Tam-AI
|
No
|
|
18
|
48
|
T1 N0 M0
|
2
|
90%
|
90%
|
neg.
|
n. d.
|
6 × FEC q3w
|
Tam
|
No
|
|
19
|
62
|
T2 N1 M0
|
2
|
80%
|
20%
|
neg.
|
0
|
|
3 × FEC – 3 × DOC q3w
AI
|
No
|
|
20
|
84
|
T2 N0 M0
|
3
|
90%
|
0
|
neg.
|
0
|
No
|
AI
|
No
|
|
21
|
72
|
T1 N0 M0
|
2
|
80%
|
80%
|
neg.
|
2 (30)
|
No
|
Tam-AI
|
No
|
|
22
|
56
|
T1 N1 M0
|
2
|
90%
|
90%
|
neg.
|
0
|
3 × FEC – 3 × DOC q3w
|
Tam-AI
|
No
|
|
23
|
51
|
T2 N1 M0
|
2
|
80%
|
30%
|
neg.
|
0
|
3 × FEC – 3 × DOC q3w
|
Tam/AI
|
No
|
|
24
|
60
|
T1 N0 M0
|
2
|
90%
|
90%
|
neg.
|
n. d.
|
No
|
Tam/AI
|
No
|
|
25
|
81
|
T2 N0 M0
|
2
|
50%
|
< 10%
|
neg.
|
0
|
No
|
Tam
|
No
|
|
26
|
56
|
T2 N0 M0
|
2
|
100%
|
10%
|
neg.
|
2 (30)
|
3 × FEC – 3 × DOC q3w
|
Tam/AI
|
No
|
|
27
|
69
|
T2 N1 M0
|
2
|
90%
|
90%
|
pos.*
|
2 (70)
|
No
|
No
|
Octreotide 50 µg 2/d
|
Survival analysis
Follow-up data were available for 26 out of 27 patients. The median follow-up was
63 months (range: 11 – 170 months). Nine patients died during follow-up and five of
22 initially non-metastatic and R0 operated patients were diagnosed with recurrence
(local recurrence and/or distant metastasis). The mean overall survival (OS) was 111
months (95% CI: 82 – 140 months), the mean DFS was 124 months (95% CI: 90 – 157 months).
The 5-year OS rate was 70% ([Fig. 4]).
Fig. 4 Kaplan–Meier survival curves of BC-NE patients.
For comparison, results from other studies published are summarized in [Table 5]. Only studies published after 2003 and including at least 20 patients with NEN were
considered.
Table 5 Prevalence, definitions, and clinical characteristics in important studies published
on NEN of the breast*.
|
Study
|
No. of patients
|
NEN definition
|
NEN identification process
|
Prevalence
|
Age (range)
|
Morphology/
initial histology
n (%)
|
IHC staining/
IHC subtype
n (%)
|
Grading
n (%)
|
Tumor size
n (%)
|
N status
n (%)
|
Outcome
|
|
* Studies and case series published after 2003 with at least 20 patients have been
listed. Numbers in parentheses are percentages and do not add to 100 in some instances
owing to rounding. Abbreviations: NEN: neuroendocrine neoplasia, SCNEC: small cell
neuroendocrine carcinoma, LCNEC: large cell neuroendocrine carcinoma, CSS: cancer
specific survival, CgA/B: chromogranin A/B, Syn: synaptophysin, NSE: neuron-specific
enolase, DRFS: distant recurrence-free survival, LRFS: local recurrence-free survival,
DSS: disease-specific survival, IDC: invasive ductal carcinoma, ILC: invasive lobular
carcinoma; MUC: mucinous, NST: no special type, BC-NST: breast cancer of no special
type, DFS: disease free survival, OS: overall survival, n. r.: not reported. 1 No SCNEC and/or LCNEC included, 2 no cases with > 50% positivity, 3 multivariate analysis
|
|
Makretsov et al. 2004 [11]
|
65
|
Positivity of single NE marker (NSE, CgA or Syn), without threshold
|
Systematic histological re-evaluation of 334 surgical specimens from 1974 – 1995
|
19.5%
|
n. r.
|
n. r.
|
n. r.
|
n. r.
|
n.r
|
n. r.
|
No prognostic significance of CgA or Syn expression
|
|
10
|
> 50% positivity of single NE marker (NSE, CgA or < Syn)
|
3%
|
IDC (NST) 5 (50)
IDC/ILC 2 (20)
IDC/MUC 2 (20)
MUC 1 (10)
|
HR+/HER2− 7 (70)
HR+/HER2+ 1 (10)
HR−/HER2+ 0 (0)
TNBC 2 (20)
|
G1 2(20)
G2 7(70)
G3 1(10)
|
n. r.
|
|
van Krimpen et al. 2004 [12]
|
40
|
Positivity of single NE marker (Syn and/or CgA), no treshold
|
Histological re-evaluation of 317 surgical specimens from 1983 – 1990
|
12,6
|
n. r.
|
n. r.
|
n. r.
|
n. r.
|
n. r.
|
n. r.
|
No prognostic significance of NE differentiation
|
|
Righi et al. 2010 [13]
|
89
|
WHO 2003
|
n.r
|
n. r.
|
Median 67 (43 – 92)
|
Solid cohesive 35 (39)
|
ER+ (83)
HER2+ (0)
|
G1 (26)
G2 (54)
G3 (20)
|
T1 (62)
T2 (31)
T3–4 (7)
|
N0 (71)
N+ (29)
|
n. r.
|
|
Median 68 (54 – 84)
|
Alveolar 10 (11)
|
ER+ (55)
HER2+ 0
|
G1 0 (0)
G2 5 (50)
G3 5 (50)
|
T1 (45)
T2 (44)
T3–4 (1)
|
N0 (72)
N+ (28)
|
|
Median 62 (39 – 88)
|
Small cell 11 (12)
|
ER+ (67)
HER2+ 0
|
G1 (0)
G2 (18)
G3 (82)
|
T1 (17)
T2 (83)
|
N0 (40)
N+ (60)
|
|
Median 71 (27 – 89)
|
Solid papillary 20 (22)
|
ER+ (100)
HER2+ 0
|
G1 (45)
G2 (45)
G3 (10)
|
T1 (47)
T2 (41)
T3–4 (12)
|
N0 (53)
N+ (47)
|
|
Median 66 (44 – 87)
|
Cellular mucinous 13 (15)
|
ER+ (92)
HER2+ 0
|
G1 (31)
G2 (69)
G3 (0)
|
T1 (50)
T2 (20)
T3–4 (30)
|
N0 (75)
N+ (25)
|
|
Wei et al. 2010 [14]
|
74
|
WHO 20031
|
Review of clinical records
|
n. r.
|
Mean 61 (28 – 72)
Median 63
|
Solid NE carcinoma
Atypical carcinoid
Large cell NE carcinoma
|
ER+ 70 (95)
ER− 3 (4)
Unknown 1 (1)
ER+ 59 (80)
ER− 14 (19)
Unknown 1 (1)
HER2+ 2 (3)
HER2− 67 (91)
Unknown 5 (6)
|
G1 2 (3)
G2 57 (77)
G3 15 (20)
|
T1 33 (45)
T2 31 (42)
T3 4 (5)
T4 6 (8)
|
N0 41 (57)
N1 31 (42)
Unknown 2 (3)
|
Significantly worse clinical outcome than IDC NST LRFS (p = 0.001), DRFS (p < 0.0001),
and OS (p = 0.002)
|
|
Riccardi et al. 2011 [15]
|
22
|
WHO 2003
|
Review of clinical records
|
n. r.
|
Median 63 (38 – 74)
|
n. r.
|
ER+ 18 (82)
ER− 4 (18)
PR+ 12 (54)
PR− 10 (45)
HER2 n. r.
|
n. r.
|
n. r.
|
n. r.
|
n. r.
|
|
Marton et al. 2012 [16]
|
31
|
WHO 2003
|
Review of clinical records; 3058 BC cases diagnosed 2001 – 2005
|
1,1%
|
61.7 (44 – 86)
|
n. r.
|
ER+ 27 (87)
ER− 4 (13)
PR+ 23 (74)
PR− 8 (26)
HER2+ 1 (3)
HER2− 30 (97)
|
G1 7 (23)
G2 19 (61)
G3 5 (16)
|
T1 12 (39)
T2 18 (58)
T3 1 (3)
T4 0 (0)
|
N0 16 (52)
N+ 15 (48)
|
Median follow-up 58.7 months (2 – 144), disease relapse in 25.8%, median time to relapse
34.3 months (14.5 – 54.1)
|
|
Rovera et al. 2013 [17]
|
96
|
WHO 2012
|
Review of clinical records, 2829 BC cases diagnosed 1992 – 2013
|
3.2%
|
Median 70 (40 – 94)
|
Solid type 38 (62)
MUC 14 (23)
Microinvasive 6 (10)
LCNEC 2 (3)
SCNEC 1 (2)
|
ER+ (90)
PR+ (75)
HER2+ 0
|
G1 (34)
G2 (64)
G3 (2)
|
T1 35 (60)
T2 20 (34)
T3 1 (2)
T4 2 (3)
|
N0 36 (77)
N+ 11 (33)
|
Median follow-up 65 months (range 2 – 242); 10-year OS 87%1
|
|
61
|
WHO 2003
|
n. r.
|
n. r.
|
n. r.
|
n. r.
|
n. r.
|
|
Zhang et al. 2013 [18]
|
107
|
WHO 20031
|
Review of clinical records, IHC confirmation
|
n. r.
|
Median 64 (25 – 95)
|
n. r.
|
ER+ 101 (94)
ER− 6 (6)
PR+ 91 (85)
PR− 16 (15)
HER2+ 3 (3)
HER2− 104 (97)
|
|
T1 48 (45)
T2 54 (50)
T3 5 (5)
T4 0 (0)
|
N0 81 (76)
N+ 26 (24)
|
Median follow-up 27 months (3 – 134); OS 85.1 vs. 92.4% (NST) (p = 0.030)
LRFS NEC (7.5%) vs. NST (2.8%) (p = 0.043)
DRFS NEC (5%) vs. NST (8.3%) (p = 0.061)
|
|
Zhu et al. 2013 [19]
|
22
|
WHO 2003
|
Review of clinical records, 7542 BC cases diagnosed 2004 – 2010
|
0.29%
|
Mean 52.5 (29 – 77)
|
n. r.
|
ER+ 20 (91)
ER− 2 (9)
PR+ 21 (95)
PR− 1 (5)
HER2+ 5 (23)
HER2− 17 (77)
|
n. r.
|
n. r.
|
n. r.
|
Mean follow-up 64.5 months (4 – 89), 95% of patients disease-free
|
|
Cloyd et al. 2014 [20]
|
284
|
WHO 2012
|
Review of SEER database (BC cases diagnosed between 2003 and 2010)
|
n. r.
|
n. r.
|
Well differentiated 148 (52.1)
Small cell 73 (25.7)
CA with NE features 42 (14.8)
Large cell 14 (4.9)
Carcinoid 7 (2.5)
|
ER+ 132 (46.5%)
PR+ 101 (35.6%)
HER2 n. r.
|
G1 28 (10)
G2 56 (20)
G3 127 (45)
Unknown 73 (26)
|
T1 87 (31)
T2 99 (35)
T3–4 51 (18)
Unknown 47 (16)
|
N0 145 (51)
N+ 103 (36)
Unknown 36 (13)
|
SCNEC: worse
DSS (OR 6.46, 95% CI: 0.88 – 47.68, p = 0.07) and OS (1.97, 95% CI: 0.47 – 8.22, p = 0.36)
compared to other neuroendocrine tumors of the breast
|
|
Kwon et al. 2014 [21]
|
32
|
WHO 2003
|
Histological re-evaluation of 1428 surgical specimens from 2012
|
2.2%
|
Median 49
|
IDC 54 (91.5)
MUC 3 (5.1)
Micropapillary 2 (3.4)
|
ER+ 55 (93)
ER− 4 (7)
PR+ 49 (83)
PR− 10 (17)
HER2+ 5 (8.5)
HER2− 54 (91.5)
|
G1 8 (14)
G2 19 (32)
G3 32 (54)
|
T1 24 (41)
T2 32 (54)
T3 3 (5)
T4 0 (0)
|
N0 24 (41)
N+ 35 (59)
|
NE differentiation associated with impaired OS (p = 0.004) and DFS (p < 0.001)3
No difference between focal and diffuse NE differentiation (OS, p = 0.986; DFS, p = 0.861),
follow-up 56 months (1 – 122)
|
|
59
|
WHO 2012
|
4.1%
|
|
Park et al. 2013 [22]
|
87
|
WHO 2003
|
Review of clinical records, 12 945 BC cases diagnosed 1984 – 2011
|
1%
|
Mean 63 (28 – 89)
|
IDC 60 (69)
IDC/MUC 17 (19.5)
IDC/ILC 8 (9.2)
Unknown 2 (2.3)
|
ER+ 86 (99)
ER− 1 (1)
PR+ 67 (77)
PR− 19 (22)
Unknown 1 (1)
HER2+ 2 (2)
HER2− 82 (94)
Unknown 3 (3)
|
G1 8 (9)
G2 67 (77)
G3 10 (11)
Unknown 2 (2)
|
n. r.
|
N0 44 (50)
N+ 39 (45)
Unknown 4 (5)
|
n. r.
|
|
Wang et al. 2014 [23]
|
142
|
WHO 2003
|
Review of SEER database (BC cases diagnosed between 2003 and 2009)
|
< 0.1%
|
Mean 64 (26 – 99)
|
n. r.
|
ER+ 77 (54)
ER− 37 (26)
Unknown 28 (20)
PR+ 53 (37)
PR− 59 (42)
Unknown 30 (21)
HER2+ n. r.
|
G1 17 (12)
G2 30 (21)
G3 60 (42)
Unknown 35 (25)
|
|
N0 52 (37)
N+ 40 (28)
Unknown 50 (35)
|
Impaired prognosis compared to BC-NST
Median OS 26 months (12 – 48)
5-year OS 53.6% (95% CI: 42.2 – 63.7)
NE differentiation (pos. vs. neg.) DSS 1.80 (95% CI: 1.36 – 2.37), p < 0.0001, OS
1.84 (95% CI: 1.50 – 2.26), p < 0.00013
|
|
Bogina et al. 2016 [24]
|
84
|
WHO 20031
|
Histological re-evaluation of 1232 surgical specimens from 2000 – 2012
|
6.8%
|
|
NST 58 (69)
ILC 5 (6)
MUC 6 (7)
Solid papillary 15 (18)
|
ER+/HER2− (Ki-67 < 14) 34 (41)
ER+/HER2− (Ki-67 ≥ 14) 43 (51)
ER+/HER2+ 4 (5)
ER−/HER2+ 1 (1)
TNBC 2 (2)
|
G1 3 (5)
G2 41 (71)
G3 14 (24)
|
T1 51 (61)
T2 20 (24)
T3–4 13 (15)
|
N0 38 (30)
N+ 31 (37)
Unknown 15 (18)
|
Worse DFS compared to BC-NST, no difference in CSS
NE differentiation (pos. vs. neg.)
DFS 3.12 (95% CI: 1.30 – 7.69), p = 0.0113
|
|
128
|
WHO 20121
|
|
10.4%
|
|
NST 95 (74)
ILC 5 (4)
MUC 7 (6)
Solid papillary 21 (16)
|
ER+/HER2− (Ki-67 < 14) 47 (37)
ER+/HER2− (Ki-67 ≥ 14) 65 (51)
ER+/HER2+ 9 (7)
ER−/HER2+ 3 (2)
TNBC 4 (3)
|
G1 6 (7)
G2 65 (68)
G3 24 (25)
|
T1 77 (60)
T2 36 (28)
T3–4 15 (12)
|
N0 64 (50)
N+ 42 (33)
Unknown
22 (17)
|
|
Roininen et al. 2017 [25]
|
43
|
WHO 2003
|
Review of clinical records, 12 945 BC cases diagnosed 2007 – 2015
|
n. r.
|
Median 66
|
n. r.
|
ER+ 41 (96)
ER− 1 (2)
Missing 1 (2)
PR+ 37 (86)
PR− 4 (9)
Missing 2 (5)
HER2+ 2 (5)
HER2− 40 (93)
Missing 1 (2)
|
n. r.
|
T1 29 (67)
T2 11 (26)
T3 2 (5)
T4 1 (2)
|
N0 24 (56)
N+ 17 (39)
Missing 2 (5)
|
Worse DFS (p = 0.024) and OS (p = 0.0028)
No difference in DDF, BCSS
Mean follow-up of NEN 35.4 months (95% CI: 23.5 – 47.2 months)
|
|
Kelten Talu et al. 2018 [26]
|
36
|
WHO 20031
|
Review of clinical records and IHC confirmation, BC cases 2007 – 2016
|
n. r.
|
Median 69.5, mean 67.4 (40 – 88)
|
IDC + NE differentiation 28 (78)
Solid NEC 2 (5)
IDC/MUC 2 (5)
MUC 2 (5)
IDC/ILC 1 (3)
Solid papillary carcinoma 1 (3)
|
HR+/HER2− 33 (91.6)
HR+/HER2+ 2 (5.6)
TNBC 1 (2.7)
|
G1 0 (0)
G2 31 (86)
G3 5 (14)
|
T1 13/36 (36)
≥ T2 21/36 (58)
|
n. r.
|
No conclusions
|
|
Lavigne et al. 2018 [27]
|
47
|
WHO 2003
|
Review of clinical records
|
n. r.
|
Median 67, mean 69 (33 – 91)
|
NST 37 (79)
ILC 2 (4)
Solid papillary carcinoma 5 (11)
MUC 3 (6)
|
ER+ 47 (100)
ER− 0 (0)
PR+ 36 (77)
PR− 10 (21)
Unknown 1 (2)
HER2+ 1 (2)
HER2− 46 (98)
|
G1 3 (6)
G2 29 (62)
G315 (32)
|
T1 28 (60)
T2 16 (34)
T3 2 (4)
T4 1 (2)
|
N0 22 (47)
N+ 18 (38)
Unknown 7 (15)
|
Impaired DFS, no difference in OS
|
|
Our study
|
27
|
WHO 20031
|
Histological re-evaluation of 465 surgical specimens from 2002 – 2006, review of clinical
records 2007 – 2013
|
4,5%
|
Median 61 (28 – 84)
|
NST 16 (59)
ILC 1 (4)
NST/ILC 1 (4)
MUC 4 (15)
NET 5 (18)
|
HR+/HER2− 23 (85)
HR+/HER2+ 2 (7)
HR−/HER2+ 0 (0)
TNBC 2 (7)
|
G1 0 (0)
G2 21 (78)
G3 6 (22)
|
T1 7 (26)
T2 16 (60)
T3–4 3 (11)
Unknown 1 (4)
|
N0 15 (56)
N+ 10 (37)
Unknown 2 (7)
|
Median follow-up 63 months (11 – 170), 5-year OS 70%
|
Discussion
Although neuroendocrine differentiation in BC is a long-known phenomenon, first described
in 1963 [6], it was not until 2003 that NEN of the breast was defined by the WHO as a distinct
subtype. Despite significant advances in the research and treatment of early and metastatic
breast cancer over the last decades [11], [12], [13], [14], [15], the exact prevalence, clinical behaviour and effective therapy standards for this
subset of BC have not been well established so far, possibly due to its low incidence
and discrepant definitions.
All patients eligible for our analysis were diagnosed with a NEN of the breast according
to WHO 2003 criteria (Syn and/or CgA > 50%). Poorly differentiated large or small
cell neuroendocrine carcinoma and well differentiated neuroendocrine tumors (NET,
G1) were excluded from this study ([Table 1]). Since the definition of NEN of the breast has changed twice in the last two decades,
the majority of cases described in our study would be currently defined as BC-NE (WHO
2012) and thus, in line with the latest NEN classification 2019, not be classified
as a true NEN of the breast ([Table 1]). However, diffuse neuroendocrine differentiation (Syn and/or CgA > 50%) in BC has
been shown to be associated with certain specific clinical features, and several published
studies on NEN of the breast report on these tumors as well ([Table 5]). In particular, the question whether
neuroendocrine differentiation in BC might have a diagnostic or therapeutic significance
has not yet been sufficiently answered.
Here we report on a series of 27 cases of BC-NE and present their clinicopathological
characteristics, survival analysis as well as NE-specific diagnostic and therapeutic
aspects and compare it with other published studies on NEN of the breast.
Since some patients were identified through clinical records review and others through
retrospective staining of neuroendocrine markers, we can only report on the actual
prevalence in the collective of 465 patients. With 21 cases identified by a systematic
morphological and immunohistochemical re-evaluation, we established a BC-NE prevalence
to be 4.5%, which is in line with the 2 – 5% estimated by the WHO [16]. However, the prevalence of neuroendocrine differentiation in the published studies
varies from less than 0.1% [17] to over 20% [18] ([Table 5]). This is due to the variable diagnostic criteria on the one hand and the NEN identification
process used in published trials on the other. Analyses that implement the 50% threshold
for Syn or CgA according to the WHO 2003 definition generally report lower a NEN prevalence
comparing to those meeting
WHO 2012 criteria without a threshold and/or using further neuroendocrine markers
such as NSE or CD56 for NEN diagnosis [18], [19], [20], [21] ([Table 5]). Moreover, trials that identify NEN cases via a review of clinical records or databases
report a generally lower and probably underestimated prevalence compared to those
which performed a systematic re-evaluation of histology slides from BC patients, since
neuroendocrine markers are not routinely used in BC diagnosis [17], [22], [23], [24].
The median age at initial diagnosis in our cohort was 61 years, which is in accordance
with the median age at diagnosis of breast cancer of no special type without neuroendocrine
differentiation (BC-NST) [25]. No differences between NEN of the breast and BC-NST in terms of age at diagnosis
have been reported in other case series [19], [26], [27]. However, several trials with large cohorts reported NEN of the breast patients
to be significantly older than BC-NST patients [17], [28], [29], [30], These discrepancies may also be due to nonuniform diagnostic criteria used in published
series: most of the studies meeting WHO 2003 criteria report NEN of the breast patients
being significantly older than BC-NST patients [17], [28], [29], [30] ([Table 5]).
The majority (60%) of patients in our cohort were diagnosed with ≥ T2 tumors, and
37% of our analysed patients had lymph node metastases. This observation, i.e., NEN
of the breast being diagnosed at a higher TNM stage than BC-NST, has also been reported
by others. Wang et al. in their study of 142 NEN of the breast patients showed that
those tumors were significantly larger, had higher stage disease and were significantly
often node-positive compared to control cohorts with BC-NST [17]. In the study by Cloyd et al. of 284 patients, NEN of the breast was associated
with relatively more advanced disease than BC-NST [31]. In their trial of 128 cases, Bogina et al. reported that NEN patients presented
with larger tumors than BC-NST patients but no difference regarding node status was
observed [19]. In contrast, some, mostly small series, reported similar TNM stages at diagnosis
between BC with and without neuroendocrine differentiation [18], [26], [27], [28]. The proposed rationale for this phenomenon in NEN of other locations is their low
grading and therefore slow growth, resulting in a lack of early symptoms. However,
the association with higher TNM stages has been also reported in NEN cohorts with
high rates of poorly differentiated tumors [17], [31].
Similar to previous studies, the majority of patients (85%) in our analysis presented
with ER-positive HER2-negative tumors ([Fig. 5]) [17], [22], [27], [32]. Previously, neuroendocrine differentiation has been shown to be significantly associated
with positive HR-status [19], [26], [30] and negative HER2-status [28], [29]. Most tumors in our analysis were G2 tumors (78%) and Ki-67 was higher than 30%
in 11 of 27 patients (41%). Similarly, NEN patients in other series were shown to
have G2 tumors significantly more often than patients with BC-NST [19], [28], whereas some studies reported NEN being
of a significantly higher histologic grade [17] and others found no association between neuroendocrine differentiation and grading
[26], [27]. These discrepancies may be due to inconsistent NEN cohorts, since particular subtypes
of NEN are associated with certain pathological features. In the trial by Cloyd et
al., 45% NEN patients presented with poorly differentiated or undifferentiated tumors.
However, 26% of NEN analyzed were SCNEC, well known for poor differentiation [33] and this entity has been excluded from several studies on NEN of the breast, including
our analysis. In contrast, studies that analyzed primarily mucinous NEN demonstrated
that the majority of these patients had well differentiated tumors [34], [35]. As mentioned above, due to different diagnostic criteria and the
fact that specific subtypes within NEN have not been reported in most analyses
(e.g., solid NEC vs. well differentiated NET vs. BC-NE vs. SCNEC/LCNEC), the comparison
and interpretation of published data is difficult ([Tables 1] and [5]).
Fig. 5 Expression of receptors and proliferative activity in breast carcinoma with neuroendocrine
differentiation. a Hematoxylin and eosin (H. E.) staining, demonstrating a solid growth pattern, complete
lack of tubular architecture and a cytology of tumor cells highly suggestive of a
neuroendocrine phenotype. b Strong expression of the pan-neuroendocrine marker synaptophysin (SYN) in all tumor
cells. c Strong nuclear expression of the estrogen receptor (ER) in > 90% of tumor cells resulting
in an ER score of 12 (scale 0 – 12). d Strong nuclear expression of the progesterone receptor (PR) in > 90% of tumor cells
resulting in an ER score of 12 (scale 0 – 12). e Complete lack of HER2 expression corresponding to a score of 0 (scale 0 – 3). f Analysis of Ki-67 protein expression reveals a proliferative activity of approximately
15%.
The question whether neuroendocrine differentiation affects the prognosis of BC patients
remains a very much debated issue. The 5-year OS rate of 70% in our cohort of patients
with BC-NE is lower than the OS in patients with BC-NST [25]. Although some smaller studies reported similar [18], [20], [21], [36] or even better [32], [37], [38] outcomes for NEN compared to BC-NST patients, the majority of published large series
demonstrated an impaired prognosis for NEN [17], [19], [26], [27], [28], [29], [30]
and most of these studies do not include any SCNEC cases, well known for having
a very poor outcome [19], [26], [27], [28], [29]. The association with poor clinical outcome was also present in multivariate analysis
after adjusting for pathological stage [17], [26], histological grade, and ER and HER2 status [19], [26], showing that neuroendocrine differentiation is an independent prognostic factor
in BC.
Expression of somatostatin receptor (SSTR) in NEN of the breast, similarly to NEN
of other sites, is a long-known phenomenon [39], potentially allowing SSTR-targeted tumor imaging and treatment, even though it
is not restricted to this subset of BC [40]. Among them, SSTR 2A is a subtype most commonly expressed in BC [41] and able to mediate the antiproliferative effect of somatostatin analogues (SSA)
in the strongest manner [42]. However, the SSTR 2A positivity rate in BC-NE has, to the best of our knowledge,
only been analyzed in one study so far [43]. This recently published retrospective analysis of 31 NEN cases reported a SSTR
2A positivity rate of 71% [43]. In our series, SSTR 2A was evaluated in 24 patients and 12 of them (50%) were SSTR
2A-positive. Based on this, five patients
received SSTR-based imaging (octreoscan or 68Ga-DOTATOC PET/CT) to confirm or exclude metastatic disease at the time of diagnosis
or to evaluate therapy response over the course of disease. It is possible that the
number of patients receiving SSTR-based imaging would have been much higher if neuroendocrine
differentiation had been identified at diagnosis and not, as was the case in the majority
of our BC-NE patients, retrospectively.
Beyond these specific diagnostic aspects, SSTR 2A can potentially be targeted with
SSA such as octreotide or lanreotide. These substances, which have been a mainstay
of antisecretory treatment in functional NEN for a long time, were also shown to have
antiproliferative activity and to be associated with a clinical benefit in some NEN
patients [44]. In NEN of other sites, which is much more common, this therapy is mainly being
considered in well differentiated NET (G1/2, Ki-67 < 10%) [45]. Current recommendations for BC-NE therapy are based on general guidelines for breast
cancer, and poorly differentiated SCNEC ([Table 1]) is the only entity with specific recommendations (i.e., platinum/etoposide-based
chemotherapy similar to small cell lung cancer). However, only a few case reports
on the treatment of BC patients with this regimen have been published so far [46], [47]. Since this rare subtype of NEN of the breast known to have a very poor outcome
has been excluded from our analysis, all patients in our study were treated with a
standard anthracycline-taxane (AT)-based chemotherapy. In our series, two SSTR-positive
BC-NE patients received SSA in combination with endocrine therapy and one of these
patients, initially diagnosed at stage IV with metastasis to lung and bones, achieved
complete remission showing no evidence of disease on radiological and SSTR-based imaging
66 months after the first diagnosis. This patient exhibited strong SSTR 2A-expressing
BC-NE G2 with a Ki-67 of 25% and not a typical well differentiated NET. Indeed, SSA
therapy has been evaluated in BC-NST in the past and showed response rates of up to
40% in a metastatic setting in phase I – II trials [48]. However, a phase III study comparing endocrine therapy with or
without octreotide in primary ER-positive BC did not show a benefit of SSA treatment
in this setting [49]. Nonetheless, none of these studies evaluated the SSTR status of tumor tissue prior
to SSA-based therapy. Here we demonstrate that SSA therapy in SSTR 2A-positive BC-NE
can be offered as an individual treatment option to selected patients, e.g., as combination
therapy in a palliative setting or in the case of contraindications to the standard
treatment. Since neuroendocrine differentiation has been shown to be associated with
impaired outcomes in several retrospective trials, further studies are needed to identify
the most appropriate treatment strategy for this BC subtype.
Declarations Section
Ethics approval and consent to participate: The study was approved by the Ethical Committee of the Heinrich Heine University
of Duesseldorf.
Consent to publish: This manuscript does not contain any details, images, or videos that might lead to
the identification of any individual patient.
Availability of data and materials section: The data that support the findings of this study are available from the authors on
reasonable request and with the permission of Tanja Fehm.
Funding: None.
Authorsʼ contribution: NK performed the data analysis and drafted the manuscript. RR collected the data
and helped to draft the manuscript. SO, KL helped to perform the IHC experiments.
MA, and SB performed the IHC experiments, the morphological evaluation and helped
to draft the manuscript, IE perform the IHC experiments and help to draft the manuscript,
CM helped to draft the manuscript. MN designed and coordinated the study, TF designed
the study, made substantial contribution to interpretation of the data and reviewed
the manuscript. MBP, ER, SM, JH, TK, BJ were involved, in interpretation of the data,
drafting of the manuscript or revising it. All authors read and approved the final
manuscript.
