Primary prostatic seminoma: a rare case report and structured literature review highlighting tumor marker discordance

Primary prostatic seminoma (PPS) is an exceptionally rare extragonadal germ cell tumor, with only isolated cases reported in the literature. Owing to its anatomical location, PPS may clinically and radiologically mimic prostate adenocarcinoma or other bulky pelvic malignancies, creating a risk of inappropriate local treatment. We report the case of a 34-year-old man presenting with a large prostatic mass and discordance between substantial tumor burden and only mildly elevated serum prostate-specific antigen (PSA; 3.43 µg/L). Serum lactate dehydrogenase (LDH) was markedly elevated (11.50 µkat/L), beta-human chorionic gonadotropin (beta-hCG) was mildly increased (5.3 IU/L), and alpha-fetoprotein remained within the normal range. Multiparametric magnetic resonance imaging and [18F]FDG positron emission tomography/computed tomography demonstrated a bulky, metabolically active prostatic tumor, but histopathological verification was essential for diagnosis. Immunohistochemistry showed strong positivity for SALL4 and c-KIT/CD117 with focal placental alkaline phosphatase expression, and negativity for prostatic, lymphoid, and non-seminomatous germ cell tumor markers, confirming seminoma. The patient was classified as good-risk according to the International Germ Cell Cancer Collaborative Group classification and achieved sustained complete remission following cisplatin-based chemotherapy. A structured literature review following PRISMA reporting principles identified 12 modern cases reported between 1990 and 2026. A recurrent observation was biochemical discordance between extensive tumor burden and low or only mildly elevated serum PSA levels. Germ cell markers, including LDH and beta-hCG, were variably elevated but lacked sufficient sensitivity and specificity to establish or exclude the diagnosis. Most patients were treated with cisplatin-based chemotherapy and/or radiotherapy, with a high rate of complete remission. PPS is a rare but highly curable malignancy. In young patients with atypical bulky prostatic masses and PSA levels disproportionate to tumor burden, early biopsy with germ cell-specific immunohistochemistry is essential. Functional imaging may support staging and response assessment, but systemic cisplatin-based chemotherapy remains the cornerstone of curative treatment.