Introduction

Small-cell carcinoma usually originates from the lung and accounts for 18% of all lung cancers. Nevertheless, the primary site can rarely be outside the lungs and pleural spaces, which are referred to as extrapulmonary small-cell carcinoma (EPSCC) (1). Besides the respiratory tract, small cell carcinoma can rarely arise from the prostate and in extremely rare cases from the seminal vesicles (2). Herein, we present a rare case of EPSCC demonstrated on fluorine-18-fluorodeoxyglucose (¹⁸F-FDG) positron emission tomography/computed tomography (PET/CT) with extensive involvement of the seminal vesicles and prostate gland.

Case Report

A 79 year-old male was admitted with acute renal failure with a history of radical radiotherapy for prostate adenocarcinoma 13 years ago. The prostate specific antigen level was not elevated. The abdominopelvic CT scan showed markedly enlarged seminal vesicles occupying most of the pelvic cavity causing bilateral ureteral obstruction, and loss of fat plane between seminal vesicles and a mildly enlarged prostate gland indicating local invasion of the tumor. ¹⁸F-FDG PET/CT demonstrated intense ¹⁸F-FDG uptake (SUV_max: 7.2) throughout the bilateral markedly enlarged seminal vesicles with diffuse involvement of the prostate (Figure 1). There was no primary pulmonary lesion or metastatic spread on either diagnostic CT of the chest or ¹⁸F-FDG PET/CT. Percutaneous core biopsies of the prostate and both seminal vesicles revealed diffuse small cell carcinoma (Figure 2). The patient was diagnosed with urogenital EPSCC, however, the origin of the tumor remained unclear. The patient succumbed to the disease prior to commencement of systemic therapy.

Literature Review and Discussion

Small-cell carcinoma usually originates from the lung and accounts for 18% of lung cancers, but very rarely the primary site is detected outside the lungs and pleural spaces, which is called EPSCC (1). Small cell carcinoma of the prostate accounts for less than 1% of all prostate cancers while there are only a few case reports of primary small cell carcinoma of the seminal vesicles (2). Seminal vesicle malignancies are mostly secondary tumors from adjacent organs such as the prostate rather than primary intrinsic tumors (3). Several different routes of invasion have been suggested, most commonly from tumor extension through the ejaculatory ducts or direct spread across the prostatic base (4). Approximately 25-40% of cases is initially diagnosed as prostatic adenocarcinoma and recurs as small cell carcinoma after initial therapy, and the median interval between diagnosis of prostatic adenocarcinoma and recurrence of small cell carcinoma is reported as 25 months (2). Small cell carcinoma commonly presents with distant metastases in up to 25% of patients with small cell carcinoma of the prostate, and with locally advanced disease in some cases due to absence of symptoms in early stages (2). The microscopic features of urogenital small cell carcinoma are similar to those seen in other organs and show high grade and poor differentiation (5). The prognosis of urogenital small cell carcinoma is poor with a median survival of less than 1 year (6). Early diagnosis and accurate staging are important since surgery with curative intent may only be considered for localized disease (7). Recommended treatment regimens for urogenital small cell cancer are similar to those for small cell carcinoma of the lung. Chemotherapy is the mainstay of treatment, with radiation therapy being used either to enhance local control or for palliation of symptoms in metastatic disease (8). ¹⁸F-FDG PET imaging has been shown to be useful for staging small cell lung cancer but the rarity of urogenital small cell cancer has precluded a similar analysis (9). However, the demonstration of marked ¹⁸F-FDG uptake in primary small cell carcinoma of urogenital origin indicates that there may be a role for ¹⁸F-FDG PET/CT scan in the staging and probable response assessment of EPSCC.

Authorship Contributions

Concept: Informed consent was obtained from the patient’s relatives, Data Collection or Processing: Amir Iravani Tabrizipour, Chuong Bui, Analysis or Interpretation: Amir Iravani Tabrizipour, Literature Search: Amir Iravani Tabrizipour, Robert Mansberg, Writing: Amir Iravani Tabrizipour, Lily Shen, Robert Mansberg, Chuong Bui, Peer-review: Externally peer-reviewed, Conflict of Interest: No conflict of interest was declared by the authors, Financial Disclosure: The authors declared that this study has received no financial support.