Rare Histological Variants of Prostate Adenocarcinoma: A National Cancer Database Analysis.

Purpose: The American Joint Committee on Cancer recognizes 6 rare histological variants of prostate adenocarcinoma. We describe the contemporary presentation and overall survival of these rare variants.
Materials and Methods: We examined 1,345,618 patients who were diagnosed with prostate adenocarcinoma between 2004 and 2015 within the National Cancer Database. We focused on the variants mucinous, ductal, signet ring cell, adenosquamous, sarcomatoid and neuroendocrine. Characteristics at presentation for each variant were compared with nonvariant prostate adenocarcinoma. Cox regression was used to study the impact of histological variant on overall mortality.
Results: Few (0.38%) patients presented with rare variant prostate adenocarcinoma. All variants had higher clinical tumor stage at presentation than nonvariant (all p <0.001). Metastatic disease was most common with neuroendocrine (62.9%), followed by sarcomatoid (33.3%), adenosquamous (31.1%), signet ring cell (10.3%) and ductal (9.8%), compared to 4.2% in nonvariant (all p <0.001). Metastatic disease in mucinous (3.3%) was similar to nonvariant (p=0.2). Estimated 10-year overall survival was highest in mucinous (78.0%), followed by nonvariant (71.1%), signet ring cell (56.8%), ductal (56.3%), adenosquamous (20.5%), sarcomatoid (14.6%) and neuroendocrine (9.1%). At multivariable analysis, mortality was higher in ductal (HR 1.38, p <0.001), signet ring cell (HR 1.53, p <0.01), neuroendocrine (HR 5.72, p <0.001), sarcomatoid (HR 5.81, p <0.001) and adenosquamous (HR 9.34, p <0.001) as compared to nonvariant.
Conclusions: Neuroendocrine, adenosquamous, sarcomatoid, signet ring cell and ductal variants more commonly present with metastases. All variants present with higher local stage than nonvariant. Neuroendocrine is associated with the worst and mucinous with the best overall survival.