Metastatic Small Cell Neuroendocrine Carcinoma of the Prostate: A Rare and Aggressive Case Report From Bangladesh

Small cell neuroendocrine carcinoma of the prostate (SCNEC) is a rare but devastatingly aggressive malignancy, carrying a median survival well under 13 months even with multimodal treatment. It may arise de novo or emerge as a treatment-resistance phenotype following androgen deprivation in conventional prostatic adenocarcinoma. A defining and clinically treacherous feature is its failure to elevate serum PSA in proportion to tumour burden-a phenomenon termed the 'PSA paradox'-which routinely delays diagnosis, particularly in resource-limited settings.

We report a 35-year-old Bangladeshi man who presented with obstructive urinary symptoms, constipation and deep pelvic pain. His serum PSA was only 0.77 ng/mL despite a 6.5 × 6.0 × 5.5 cm prostate mass with liver metastases, extensive osteoblastic bone deposits (SUVmax ~18 on 18F-FDG PET/CT), left hydronephrosis and regional lymphadenopathy. Initial TRUS-guided biopsy was reported as Gleason 5 + 5 = 10 adenocarcinoma. Given the PSA-disease burden mismatch, biopsy slides were immediately re-evaluated; haematuria and acute urinary retention necessitated urgent TURP on 4 December 2024, which confirmed a pure de novo SCNEC with diffuse synaptophysin positivity and a Ki-67 index exceeding 60%. GATA3 and p40 were negative. Renal function was confirmed adequate before platinum therapy following palliative TURP(serum creatinine 1.2 mg/dL); etoposide-cisplatin (EP) chemotherapy was administered for six cycles with standard hydration, achieving a marked metabolic response on interim PET/CT. Consolidative pelvic IMRT (55 Gy/20 fractions) followed. Despite this approach, the disease relapsed within 3 months; second-line docetaxel produced no meaningful response. The patient died approximately 11 months from diagnosis.

This case underscores the critical importance of recognising the PSA paradox in younger patients with bulky pelvic disease, the indispensable role of a comprehensive IHC panel in confirming the neuroendocrine phenotype and the urgent need for novel therapeutic strategies in this near-universally lethal malignancy.