Histologic variants of acinar prostate carcinomas: Clinicopathologic importance

Acinar carcinoma comprises more than 90% of prostatic adenocarcinomas and is characterized by a small gland proliferation with an infiltrative growth pattern. The numerous, variably-defined histological variants of prostatic adenocarcinoma can prove to be diagnostic challenges and show prognostic differences when compared to the usual acinar carcinoma, thus emphasizing the importance in accurate recognition. Variants of acinar prostatic adenocarcinoma include the atrophic, pseudohyperplastic, microcystic, foamy gland, mucinous (colloid), signet ring-like cell, pleomorphic giant cell, and sarcomatoid variants. The atrophic, pseudohyperplastic, microcystic, and foamy gland variants can be challenging to diagnose due to their deceptively benign appearance. While the atrophic, pseudohyperplastic, microcystic, and foamy gland variants usually present as low-grade malignancies (Gleason score 6-7), the mucinous (colloid), signet ring-like cell, pleomorphic giant cell, and sarcomatoid variants often present as high-grade malignancies (Gleason score >7) and are usually associated with a worse prognosis. Small cell carcinoma is not considered as a variant of acinar carcinoma, is classified under neuroendocrine tumors, and is recommended not to be assigned a Gleason score. Small cell carcinoma is often preceded by a diagnosis of acinar adenocarcinoma, rarely presents as a de novo tumor, and, as in other organs systems has an aggressive clinical course. In this review article, we discuss variants of prostatic acinar carcinomas and briefly discuss small cell carcinoma. Awareness of variants of acinar prostate carcinoma and their clinicopathologic features is essential to rendering an accurate diagnosis and clinical management of patients with these tumors.