Keywords ASCO/CAP guidelines 2018 - equivocal - FISH - HER2 - invasive breast cancer
Introduction
Breast cancer is the most common and leading cancer in Indian women.[1 ] Hormonal status and HER2 expression are mandatory in diagnosed case of invasive
breast cancer (IBC) as they dictate the further management and prognosis. The 2007
American Society of Clinical Oncology (ASCO) guidelines has a mandate that HER2 immunohistochemistry
(IHC) should be evaluated in every IBC.[2 ]
The American Society of Clinical Oncology/College of American Pathologists (ASCO/CAP)
introduced guidelines for IHC interpretation of HER2 in 2007, which was revised in
2013 to include maximum number cases that would benefit by anti-HER2 targeted therapy
and suggested HER2 testing by fluorescence in situ hybridization (FISH) in cases with
HER2 equivocal results on IHC.[3 ] Following which cases reported as HER2 equivocal by FISH technique was a challenge
to manage as definite guidelines were not established.
The ASCO/CAP guidelines was revised in 2018 to limit HER2 equivocal category.[4 ] HER2 scoring by FISH was divided into five groups. The expert panel recommended
that HER2 0, +1, and +2 scoring by IHC with HER2/chromosome enumeration probe 17 (CEP17)
ratio lower than 2 and HER2 signals/cell if equal to or more than 4 and less than
6 is now considered as negative.[5 ] Although few studies have evaluated the impact of 2018 updated ASCO/CAP guidelines,
the implications of the same in response to treatment in the clinical practice are
still variable. So, it is important to categorize FISH results into various groups
especially in equivocal cases on IHC.[6 ]
[7 ]
[8 ]
[9 ]
Updated guidelines recommend upfront HER2 testing by FISH that is much sensitive but
it has a longer turnaround time and is not feasible in smaller settings considering
the resources and cost. In Indian scenario, common practice is to confirm only HER2
equivocal results reported on IHC by sensitive FISH technique as IHC is definitive
when results are either positive or negative.
The purpose of this study was to evaluate IHC equivocal cases and compare the findings
with FISH results and also assess how the revised 2018 guidelines affected the final
HER2 status.
Materials and Methods
We retrospectively reviewed HER2 FISH results of 502 IBC cases that were reported
equivocal on IHC from January 2016 to January 2022. Specimens included core needle
biopsies, wide local excision, simple and modified radical mastectomy, biopsies from
metastatic sites. and effusion fluids. All cases were evaluated for hormonal receptor
and HER2 status by IHC prior to FISH testing. Only equivocal cases reported on IHC
and subjected for FISH were included in the study. The FISH results were interpreted
based on 2013 and 2018 ASCO/CAP guidelines and change in HER2 status was compared.
Institutional review committee approval was obtained.
IHC: Automated IHC was done formalin-fixed paraffin-embedded (FFPE) tissue with appropriate
control for estrogen receptor (ER) (clone SP-1, RTU, Ventana, Arizona, USA), progesterone
receptor (PR) (clone 1E2, RTU, Ventana, Arizona, USA), and HER2 (clone, 4B5, Ventana,
Arizona, USA) was performed on automated slide stainer, Ventana Benchmark XT. The
results were interpreted according to the ASCO/CAP 2018 guidelines.
FISH: Technique was performed using Zytovision HER-2dual probe kit (Zytovision, Germany)
on interphase invasive tumor nuclei of FFPE. The following probes were used: LSI HER-2/neu
(spectrum green) for HER-2 gene locus (17q11) and CEP 17 (spectrum orange) for the
α satellite DNA sequence at the centromeric region of chromosome 17.
Paraffin sections of 5 micron thick were transferred onto poly-L-Lysine coated slides
and allowed to dry and placed in hot air oven at 90°C for 1 hour, and then placed
on slide warmer at 60 to 70°C for 10 minutes. The slides were deparaffinized in xylene
at room temperature for 20 minute and rehydrated with downward grading of alcohol
from 100%. The washed slides were then transferred into pretreatment solution for
20 minutes at 90°C in water bath. Slides were then placed in humidity chamber at 37°C
after adding few drops of pepsin for 15 minutes, and then dehydrated in graded concentration
of alcohol up to 100%. Dual-labeled probes of 0.5 mL were added and denatured for
12 minutes at 75°C followed by hybridization for 17 hours at 37°C.
After posthybridization, two washes with wash buffer were performed at 37°C. Slides
were then dehydrated in graded concentration of alcohol up to 100%. Ten microliters
of DAPI were applied on completely dried slides and coverslip was gently placed. The
slides were screened by fluorescent microscope (Olympus, United States) using appropriate
filters (DAPI - 4',6-diamidino-2-phenylindole, FITC - Fluorescein isothiocyanate,
and SpO - Spectrum orange). Signals were counted in at least 20 cells for both the
HER-2/neu gene and chromosome 17 centromere signals under oil immersion. Signal were
counted and results were interpreted based on 2018 and 2013 guidelines.
While FISH interpretation, care was taken to ensure only areas with equivocal IHC
findings were assessed.
In group 2 to 4 cases with equivocal IHC results, recounting was done in 20 cells
by an observer blinded to previous results. Suitable area on the slide was marked
by pathologist to ensure adequate tumor and the corresponding equivocal area was studied,
and in no case issue of repeat on alternate block was encountered.
Results
The study consisted 502 cases of IBC. Sampled tissues were from the following sites:
458 (91.2%) from the primary site of malignancy, 36 (7.9%) from the metastatic sites
(liver, ovary, lung, axillary and clavicular lymph node, cerebellum, bone marrow,
pleural biopsy, and ascitic fluid); and 8 (1%) cases were from a recurrent lesion.
Two cases from the cytology cell block were done on pleural and ascitic fluid each.
Testing was done on specimens obtained by surgical excision (n = 229), core needle biopsies (n = 271), and cell block (n = 2)
Age group of patients with 50 years and below were 240 (47.8%) and above 50 years
were 262 (52.2%) cases. Overall median age was 63.5years (25–82). HER2 expression
pattern based on age did not show association with age.
Histomorphologically, majority of the cases (95.8%) were invasive carcinoma (ductal),
followed by invasive lobular carcinoma (1.3%). Hormonal and HER2 status along with
morphologic type is tabulated ([Table 1 ]).
Table 1
Histologic type of breast cancer with hormonal receptor status by IHC and HER2 expression
by FISH
Histologic diagnosis
Hormonal status
No of cases
HER2 FISH
Positive
Negative
Invasive carcinoma, ductal (n = 481)
ER and PR positive
297
143
134
ER positive, PR negative
54
34
20
ER negative, PR positive
19
09
10
ER and PR negative
111
65
46
Invasive lobular carcinoma (n = 07)
ER and PR positive
06
03
03
ER and PR negative
01
00
01
Metaplastic carcinoma (n = 04)
ER and PR positive
01
00
01
ER positive, PR negative
01
01
00
ER negative, PR positive
01
01
00
ER and PR negative
01
00
01
Cribriform carcinoma (n = 02)
ER and PR positive
02
01
01
Mixed cribriform+ tubular (n = 02)
ER and PR positive
02
00
02
Mucinous carcinoma (n = 02)
ER and PR positive
02
00
02
Invasive papillary carcinoma (n = 02)
ER and PR positive
02
01
01
Apocrine carcinoma (n = 01)
ER negative, PR positive
01
00
01
Mucinous cystadenocarcinoma (n = 01)
ER and PR negative
01
01
00
Abbreviations: FISH, fluorescence in situ hybridization; ER, estrogen receptor; IHC,
immunohistochemistry; PR, progesterone receptor.
HER2-FISH results were scored based on both 2013 and 2018 guidelines. With the implementation
of 2018 guidelines, the interpretation of HER2 status for a total of 29 (5.7%) cases
changed. Findings are discussed below:
Cases unchanged according to both 2013 and 2018 guidelines; 258 (51.3%) HER2 positive
and 217 (43.2%) HER2 negative cases continued to have the same HER2 status.
HER2 equivocal cases as per 2013 guidelines scored HER2-negative, 25 (5.0%) cases
scored HER2 equivocal in 2013 scoring schema were HER2 negative. These cases expressed
HER2/CEP17 ratio less than 2.0 and average HER2 copy number ≥ 4 and < 6/cell.
Two cases grouped in ISH group 2 and reported HER2-negative was diagnosed HER2- positive
as per 2013 guidelines.
Following were the overall findings of the 502 cases of IBC when categorized into
five groups, based on HER2 FISH interpretation described in 2018 guidelines: 219 (43.6%)
cases were classic amplified (positive) belonged to group 1, 217 (43.2%) cases classic
nonamplified (negative) fell into group 5, 02 (0.4%) patients were in group 2, 39
(7.8%) cases belonged to group 3 (positive) ([Fig. 1A ]), and 25(5.0%) cases were in group 4 (negative) ([Fig. 1B ]).
Fig. 1 Representative HER2 fluorescence in situ hybridization; green signal localized to
HER-2 gene on chromosome 17, orange signal localized to CEP 17 region. (A ) Nonclassical amplification—Group 3, reported as HER2 positive with equivocal IHC
result, HER2/CEP17 ratio is 1.3 (<2) and average HER2 copy number signal/cell is 6.5.
B: Scored equivocal as per 2013 criteria but was negative and fell in group 4 according
to 2018 guidelines, HER2/CEP17 ratio: 1.2 and average HER2 copy number 4.5 signal/cell.
The hormonal receptor status was analyzed with respect to the HER 2 groups ([Table 2 ]). About 70.5 and 60.8% of cases with ER and PR positivity were reported as HER2-positive.
About 29.5 and 39.1% cases with ER and PR negativity showed HER2 positivity, respectively,
among total number of HER2-positive cases.
Table 2
Distribution of hormonal status expression in different groups as per updated 2018
ASCO/CAP guidelines
Hormonal status
Group 1 (n = 219)
Group 2 (n = 02)
Group 3 (n = 39)
Group 4 (n = 25)
Group 5 (n = 217)
Total cases (n = 502)
ER positive
149 (40.5%)
01(0.2%)
33(9%)
21(5.7%)
163(44.4%)
367
ER negative
70(51.8%)
01(0.7%)
06(4.4%)
4(03%)
54(40%)
135
PR positive
123(37%)
01(0.3%)
34(10.2%)
21(6.3%)
154(46.2%)
333
PR negative
96(56.8%)
01(0.6%)
05(3.0%)
04(2.3%)
63(37.2%)
169
Abbreviations: ASCO/CAP, American Society of Clinical Oncology/College of American
Pathologists; ER, estrogen receptor; PR, progesterone receptor.
Discussion
The ASCO/CAP guidelines were revised in 2013 with the intention of maximizing the
patients who can benefit from anti-HER2 targeted therapy and minimizing false-negative
results.[3 ] With the revision, the equivocal results increased in frequencies and posed a problem
in clinical decision making. In that context, the ASCO/CAP guidelines was updated
in 2018; the significant modifications in the updated guidelines were refining the
interpretation criteria in arriving at the most accurate HER2 status designation (positive
or negative) based on concomitant FISH and IHC results. Single institutional study
found 502 HER2-IHC equivocal cases subjected to FISH. When HER2 FISH results were
compared as per 2013 and 2018 ASCO/CAP guidelines, overall HER2 status was changed
in 27 cases (5.4%). 25 equivocal cases were HER2 negative and 02 HER2-positive were
interpreted negative( [Table 3 ]).
Table 3
Comparison of HER2 FISH results as per 2013 and 2018 ASCO/CAP guidelines
FISH status
2013 guidelines (n , %)
2018 guidelines (n , %)
Difference
(%)
Negative
217 (43.2)
244 (48.6)
+5.4
Equivocal
25 (5.0)
00
−5.0
Positive
260 (51.8)
258 (51.4)
−0.4
Abbreviations: ASCO/CAP, American Society of Clinical Oncology/College of American
Pathologists; FISH, fluorescence in situ hybridization.
HER2 amplification (group 1) was seen in 219 (43.6%) cases and HER negative with classic
nonamplification (group 5) in 217 (43.2%) cases. Data when compared with other studies
is variable, one possible explanation is our study considered only cases with equivocal
results on IHC.[6 ]
[10 ] Two (0.4%), 39(7.8%), and 25 (5.0%) cases after HER2 testing by FISH fell under
group 2, 3, and 4 category, respectively, which totally accounted for 13.1% cases.
As per the 2018 ASCO/CAP focused HER2 update approximately 5% of breast cancer cases
are reported to fall into these uncommon categories of groups 2 to 4.[11 ]
The HER2 status in ISH group 2 is uncommon and only 02 (0.4%) cases were encountered.
Other studies have also found very few cases in this group.[6 ]
[11 ]
[12 ] These cases were considered as HER2-positive as per 2013 guidelines. Clinical trials
with anti-HER2 therapy had no significant effect on patients; hence, to offer definitive
diagnosis, such cases should be recounted in at least 20 cells by an observer blinded
to the previous results and if the finding is concordant, it should be reported as
negative and in discrepant cases are to be resolved after carefully assessing the
internal procedure of the FISH testing.[4 ]
[12 ]
There were 39 (7.8%) cases in ISH group 3; this finding was variable among different
studies.[6 ] A ratio of <2.0 can be attributed to the increase in both HER2 and control centromere
signals. A remarkable variability of IHC score for cases in this group was observed
across different laboratories.[6 ]
[11 ]
[12 ]
[13 ]
[14 ] The positive rate of IHC in this group ranges from 8.3 to 75%; this marked variability
was observed across different laboratories.[6 ] Considering the heterogeneity in HER2-IHC results, 2018 guidelines recommend that
cases with concurrent IHC score of 2 +/3+ were categorized as HER2 positive.
Twenty-five (5.0%) cases fell in ISH group 4, similar to the finding by Wang et al.[6 ] 2013 guidelines resulted in increased number of equivocal cases that posed a challenge
in management of cases; with revised 2018 guidelines the cases are better stratified
as equivocal category does not exist.[15 ] It is advised not to repeat FISH especially in cases with ISH threshold ratio close
to positivity as there is higher likelihood of different result by chance. CEP17 copy
number gain is a genetic change commonly observed during dual-probe HER2 ISH for breast
cancer, with reported frequency of 3 to 46% in IBC.[16 ] However, subsequent studies revealed CEP17 copy number gain results from amplification
or copy number gain in the centromeric or pericentromeric region and not polysomy17.[17 ] 2013 guidelines recommend repeated HER2 testing using alternate probe for CEP17
or other gene in chromosome17 for ISH equivocal cases; however, 2018 ASCO/CAP guidelines
does not advocate use of any alternate probe to identify the true polysomy due to
limited evidence on its analytical and clinical validity.[4 ]
With the availability of anti-HER2-targeted agents, accurate assessment of HER2 status
is important in identifying the patients who will respond to the therapy and avoid
use of drugs in false positive cases. FISH assay has demonstrated a greater accuracy
compared with IHC.[5 ] Current guidelines has simplified and stratified reporting of HER2 status; however,
issue of intratumoral HER2 heterogeneity is encountered in certain subsets and is
more common in equivocal HER2 protein expression cases. Studies have found cases with
HER2 heterogeneity have incomplete response to targeted therapy and decreased disease-free
survival. CAP recommends to document the amplification of HER2 in subpopulation if
it comprises >10% of tumor cells. It is prudent to know that while assessing for receptor
status change upfront by FISH after chemotherapy at metastatic sites, polyploidization
could result in false HER2 amplification, and careful evaluation using dual-probe
ISH with concomitant IHC review is recommended.[18 ]
Overall when hormonal receptor status was compared with HER2 amplification, 182 (36.2%)
cases were positive for both ER and HER2; these finding are in support with other
studies ranging from 8 to 40%.[6 ] Seventy-seven (15.3%) and 101 (20.1%) cases were amplified (classic and nonclassic
types) with negative ER status and PR status, respectively.
Updated 2018 ASCO/CAP guidelines focuses on dual-probe ISH groups (2, 3, and 4) with
less common ISH patterns, and significant recommendation is concomitant IHC review
for these ISH groups to achieve the most accurate determination of HER2 status. In
Indian scenario, the practice is quite different, FISH is not routinely followed as
first line test to detect HER2 amplification, and only cases with equivocal expression
on IHC are subjected for FISH. The common practice is performing upfront IHC to identify
the protein expression; nevertheless, the impact of the updated 2018 guidelines was
similar to other studies.[5 ]
[6 ]
Data from our study depict a 5.4% increase in HER2 negativity rates from 217 (43.2%)
to 244 (48.6%) cases. Very small fall in positivity rates 02 (0.4%) was noted and
these positive cases fell into group 2 category ([Table 3 ]). As per Kong et al study, 27 (5.4%) equivocal cases were changed to HER2 negative
as per the 2018 guidelines. Variation in HER2 status reported in other studies is
around 5 to 10%.[20 ] These findings explain the impact of the revised guidelines in identifying more
patients with HER2 negative status in whom anti-HER2 targeted agents is avoided. The
patients in group 2 and 4 categories are associated with low HER-2 protein expression,
and there has been no strong evidence of treatment benefit in these two groups; hence,
the updated 2018 guidelines identifies the false positive FISH cases to avoid unwarranted
treatment.[21 ]
Our study presents the frequency and characteristic of different HER2 FISH categories
and reports the Indian database on the 2018 ASCO/CAP guidelines. The findings suggest
that cases are better stratified in identifying patients who benefit on receiving
anti-HER2 therapy. With the 2018 guidelines, FISH results are more definitive in treatment
making as the equivocal category is removed. As majority of equivocal cases are categorized
as HER2 negative and this explains the increase in negative rates of HER2 by FISH.[22 ] Only long-term clinical outcome of these patients will determine will the validity
of the updated guidelines.