Primary signet ring cell carcinoma of prostate: A rare case report and review of literature

Primary signet ring cell carcinoma (PSRCC) of the prostate is an extremely rare variant of prostatic adenocarcinoma. A PubMed search of the English language literature from January 2000 to June 2020 using the keywords "signet ring cell carcinoma" and "prostate," identified 20 cases of PSRCC of the prostate. On the basis of the combined data from this study and the literature review, 21 such patients were evaluated for clinical characteristics, histologic diagnoses, special and immunohistochemical staining, and treatment. The mean age at the diagnosis was 68.47 years (range 50-85 years). The prostate-specific antigen (PSA) levels varied from 0.19 to 6658 ng/mL, with a mean of 509.15 ng/mL. Most (50%) presented with Stage 3 cancer. The most common Gleason grade group was 5 (Gleason score 9 to 10), seen in 61.5%. The extent of signet ring cell involvement of the specimen when reported was documented as more than 20% of the tumor-containing signet ring cells, with a range of 25%-90%. For pathologic diagnosis, the most common special stains performed were periodic acid-Schiff and Alcian blue, and among the immunohistochemical stains, the most common were PSA, CK20, and prostate-specific acid phosphatase. A detailed clinicoradiological and pathological workup is essential to rule out primary from other common sites, in view of its grave prognosis and lack of an established treatment protocol.