Unusual Type of Acinar Adenocarcinoma of the Prostate With Low PSA: A Histopathological Report of Two Cases of Pleomorphic Giant Cell Adenocarcinoma

<b>Introduction:</b> Prostate adenocarcinoma is among the leading malignant neoplastic processes in overall incidence and among the leaders of cancer-related deaths. Clinically, there is a higher risk of development in males over 50, and suspicion is increased in all cases of elevated prostate-specific antigen (PSA) levels. While the most common histologies are of conventional ductal and acinar prostatic adenocarcinoma, there are some exceedingly rare histological patterns and subtypes that vary from conventional carcinomas not only in their histological makeup but also in their presentation and aggressiveness. <b>Case Presentations:</b> Herein, we report two cases of male patients aged 75 and 60 years who presented to our institution with the leading complaint of urinary retention and gross hematuria and concomitant hydronephrosis. In both patients, the PSA levels were within normal reference values. As such, they were scheduled for transurethral resection of the prostate, with histopathology of the resected specimens showing a pleomorphic tumor process with foci of pseudoacinar structures comprised of large atypical cells with large hyperchromic nuclei, some of which had a monstrous appearance, solid tumor cell aggregates, sheets, and single tumor cells invading the parenchyma, represented mainly by large tumor cells with macroanisokaryosis, nuclear hyperchromasia, and pronounced pleomorphism. <b>Conclusion:</b> Pleomorphic giant cell prostatic carcinomas rarely present with elevated PSA or specific imaging findings and are often diagnosed incidentally, further contributing to their rarity.