Metastatic Squamous Cell Carcinoma of Prostatic Origin: Identification Through Next Generation Sequencing and Treatment With Pembrolizumab: A Case Report

Squamous cell carcinomas (SCCs) of prostatic origin are rare, representing 0.5% to 1% of all prostate carcinomas. They may be present at the diagnosis but are often discovered as a transformation of an adenocarcinoma previously treated with radiotherapy or androgen deprivation therapy. The few cases described in the literature indicate an aggressive evolution, with a median survival around 14 months. This case describes a 60-year-old man who initially had metastatic adenocarcinoma of prostatic origin that evolved toward a SCC. He was treated with chemotherapy followed by pembrolizumab for maintenance. The patient maintained a response for more than 2 years and died shortly after progression of his initial adenocarcinoma. The prostatic origin of the carcinoma was identified through next generation sequencing (NGS), a technology used for the rapid and throughout sequencing of the genome. Although there was a suspicion of transformation to SCC, the origin remained unclear until the NGS provided supporting evidence.