Keywords
68 Ga-prostate-specific membrane antigen - bone metastasis - extrapleural solitary fibrous
tumor - false-positive result - prostate cancer
Introduction
Prostate cancer (PC) is considered the second most common type of cancer in men worldwide,
with an estimated 1,3 million new cases in 2018.[1 ] Bones are the most common site of distant metastasis in PC and occur in approximately
70%–84% of patients in the advanced stage.[2 ] Several studies have confirmed the high detection rate and the excellent diagnostic
performance of the positron emission tomography–computed tomography (PET-CT) study
with 68Ga-labeled prostate-specific membrane antigen (68Ga-PSMA) in high-risk staging
and in the recurrence of PC.[3 ],[4 ] An accurate detection of the presence of bone metastases is important throughout
the course of PC disease to select an ideal treatment strategy and reduce the potential
for its possible complications.[5 ]
However, despite the high sensitivity and specificity for this pathology, the increase
in the uptake of 68Ga-PSMA can also occur in normal structures,[6 ] benign lesions,[7 ] and other malignant tumors.[8 ]
Extrapleural solitary fibrous tumor (ESFT) is a rare mesenchymal neoplasm located
in the extremities. Preferably affect patients in the fifth decade and have no gender
predilection. The majority is benign and healed by complete excision of the lesion.
However, 10%–30% of cases have aggressive biological behavior with late recurrences
and/or metastases.[9 ]
In this case report, we intended to advise oncologists, urologists, and nuclear medicine
physicians about the possibility of identifying other pathologies using this modality
of diagnostic imaging and thus preventing possible unnecessary treatments from being
performed on patients with PC.
Case Report
A.T.P, male, 69 years old, in June 2018, reported a tumor associated with pain in
the soft-tissue region of the left forearm. Imaging examinations and a biopsy of the
lesion were performed, and a high-grade malignant ESFT was identified. The patient
was then submitted to neoadjuvant chemotherapy associated with local radiotherapy
and later to marginal resection of the lesion with free margins in the pathological
examination.
Six months later, during routine follow-up with his urologist, the patient presented
a prostate-specific antigen value of 9.04 ng/mL. He underwent a multiparametric magnetic
resonance imaging of the prostate, which demonstrated a highly suspected peripheral
prostatic abnormality for clinically significant neoplasia (Prostate Imaging-Reporting
and Data System 4). A biopsy of the prostate was then performed by transrectal ultrasound,
and the anatomopathological study was compatible with prostate adenocarcinoma, Gleason
9 (4 + 5) in one fragment in the left apex and in two fragments in the left middle
third and Gleason 7 (3 + 4) in a fragment at the apex on the right.
In order to complete the PC staging, a PET/CT using a 68Ga-PSMA study was requested.
The study demonstrated multiple focal areas of abnormal uptake in the prostate with
standard uptake value maximum (SUVmax ) up to 5.0 and also a single diffuse intramedullary lesion in the right humerus with
SUVmax = 10.8 [Figure 1 ],[Figure 2 ],[Figure 3 ]. No signs of lesions were identified in the pelvic lymph nodes or in the other bones.
Figure 1 Full-body image in the maximum intensity projection showing the abnormal uptake of
68 Ga-labeled prostate-specific membrane antigen in the right humerus (arrow)
Figure 2 Axial slices from positron emission tomography-computed tomography fusion (left)
and low-dose computed tomography (right) demonstrating the intramedullary uptake of
68 Ga-labeled prostate-specific membrane antigen in the right humerus with a standard
uptake value maximum of 10.8
Figure 3 Coronal slices from positron emission tomography-computed tomography fusion (left)
and low-dose computed tomography (right) demonstrating the intramedullary uptake of
68 Ga-labeled prostate-specific membrane antigen in the right humerus
By the fact that the bone lesion presents in an uncommon site of PC metastasis, because
it does not have common anatomical features of PC, and because the patient had already
been treated for a high-grade solitary fibrous tumor (SFT), a biopsy of the humeral
lesion was performed to identify its etiology.
Finally, the histopathological and immunohistochemical studies confirmed that the
humerus lesion was a metastasis of the SFT and the patient received specific treatment
for SFT and specific hormone therapy for PC. The radical prostatectomy was contraindicated,
which was the initially planned procedure.
Discusssion
68Ga-PSMA became an important tool in the diagnosis of patients with PC.[3 ] Despite the high sensitivity and specificity for this pathology, the increased uptake
of this radioindicator can also occur in normal structures,[6 ] benign lesions,[7 ] and other malignant tumors.[8 ]
In this report, we identified, for the first time, during the staging of a high-risk
PC, an ESFT metastasis. There are an increasing number of reports on the accumulation
of 68Ga-PMSA in malignant lesions in addition to PC,[10 ] and they have already been described in the literature as an overexpression of PSMA
in neovascular endothelium of different types of solid epithelial cancer and different
malignant soft-tissue tumors,[8 ] which may explain the presence of PSMA uptake in ESFT, and represent an important
pitfall in the clinical use of this diagnostic modality. This knowledge is highly
relevant in the interpretation of these studies in patients with PC, providing an
adequate direction for treatment.
The present case demonstrates that, although 68Ga-PSMA can be useful in the diagnosis
of PC, it can also present possible false-positive results, especially in patients
who have already been diagnosed with other malignancies. Thus, physicians should be
aware of this when using this diagnostic modality to decide the best treatment option
and avoid unnecessary procedures to the patients.
Declaration of patient consent
The authors certify that they have obtained all appropriate patient consent forms.
In the form the patient(s) has/have given his/her/their consent for his/her/their
images and other clinical information to be reported in the journal. The patients
understand that their names and initials will not be published and due efforts will
be made to conceal their identity, but anonymity cannot be guaranteed.
