Consolidative Prostate Radiotherapy in de Novo Oligometastatic Mixed Small Cell Neuroendocrine Prostate Cancer: A Case Report

Small cell neuroendocrine carcinoma of the prostate is a rare and aggressive variant, and its de novo coexistence with acinar adenocarcinoma is exceptional.We present the case of a 67-year-old man with a history of treated gastric adenocarcinoma who presented with dysuria and a prostate-specific antigen (PSA) level of 14.1 ng/mL.Multiparametric magnetic resonance imaging (MRI) revealed an 11-mm Prostate Imaging-Reporting and Data System (PI-RADS) 4 lesion of the left peripheral zone.Transrectal biopsy showed a mixed tumor combining acinar adenocarcinoma (Gleason score 5+5=10) and a focal small cell carcinoma component, diagnosed on morphology and positive for synaptophysin and chromogranin A (Ki-67 index 25%).Computed tomography showed no visceral or nodal disease, and bone scintigraphy revealed four bone metastases.The disease met the European Society for Radiotherapy and Oncology-American Society for Radiation Oncology (ESTRO-ASTRO) definition of oligometastatic disease, although two extraaxial lesions classified it as high-volume according to CHAARTED criteria.After multidisciplinary discussion, the patient received three cycles of cisplatin and etoposide with combined androgen blockade, followed by consolidative moderately hypofractionated intensity-modulated radiotherapy (IMRT) to the prostate and seminal vesicle base (68 Gy in 25 fractions), with only grade 1 genitourinary toxicity.Follow-up bone scintigraphy showed markedly decreased uptake at all known sites, without new lesions.Under continued androgen deprivation, the patient remained asymptomatic, without evidence of progression on conventional imaging, at 16 months, with a PSA level of 0.006 ng/mL.This single case shows that consolidative prostate radiotherapy combined with platinum-based chemotherapy and androgen deprivation is feasible and welltolerated in a selected patient with de novo oligometastatic mixed adenocarcinoma-small cell carcinoma of the prostate.Its specific contribution to the outcome cannot be determined, and follow-up remains short.PSA mainly reflects the adenocarcinoma component and should not be used alone to monitor mixed tumors.