Cancer of unknown primary finally revealed to be a metastatic prostate cancer: a case report

Abstract

The vast majority of patients with metastatic prostate cancer present with bone metastases and high prostate specific antigen (PSA) level. Rarely, prostate cancer can develop in patients with normal PSA level. Here, we report a patient who presented with a periureteral tumor of unknown primary site that was confirmed as prostate adenocarcinoma after three years with using specific immunohistochemical examination. A 64-year old man was admitted to our hospital with left flank pain associated with masses on the left pelvic cavity with left hydronephrosis. All tumor markers including CEA, CA19-9, and PSA were within the normal range. After an exploratory mass excision and left nephrectomy, the pelvic mass was diagnosed as poorly differentiated carcinoma without specific positive immunohistochemical markers. At that time, we treated him as having a cancer of unknown primary site. After approximately three years later, he revisited the hospital with a complaint of right shoulder pain. A right scapular mass was newly detected with a high serum PSA level (101.7 ng/ml). Tissues from the scapular mass and prostate revealed prostate cancer with positive immunoreactivity for P504S, a new prostate cancer-specific gene. The histological findings were the same as the previous pelvic mass; however, positive staining for PSA was observed only in the prostate mass. This case demonstrates a patient with prostate cancer and negative serological test and tissue staining that turned out to be positive during progression. We suggest the usefulness of newly developed immunohistochemical markers such as P504S to determine the specific primary site of metastatic poorly differentiated adenocarcinoma in men.

Keywords: Cancer of unknown primary; Metastatic prostate cancer; P504S.

Fig. 1

Abdomen CT and PET scan findings at 1st visit. Abdomen CT (A) showed an approximately 3.0×2.5cm sized conglomerated lymph nodes enlargement (arrow) in left external iliac area with compressing the left distal ureter. PET scan (B) revealed a hypermetabolic mass (SUV=5.3) on the left external iliac node area (arrow).

Fig. 2

Chest CT (A, B) and bone scan (C) findings at 3 years later. Chest CT showed a 8.4cm sized mass (arrow) on the right scapular and glenoid fossa (A) and a 2.3cm sized mass (arrow) on the anterior chest wall (B). Bone scan revealed hot uptakes on the ribs and the right scapular (C).

Fig. 3

Pathologic features with immunoistochemical stainings for PSA and P504S (A: pelvic mass, B: scapular mass, C: prostate biopsy). A; The pelvic mass showed poorly differentiated carcinoma cells with hyperchromatic nuclei and small amount of cytoplasm. These tumor cells showed negative immunoreactivity for PSA but positive immunoreactivity for P504S. B; The scapular mass showed infiltrating poorly differentiated carcinoma cells, with the same histologic features and immunoreactivity for PSA and P504S to these of the previous pelvic mass. (A) C; The prostate biopsy demonstrated adenocarcinoma cells, with Gleason score 9 (4+5). Tumor cells demonstrated the same histological features to these of the previous pelvic and scapular masses but positive immunoreactivity for both PSA and P504S.