Metastatic prostate adenocarcinoma to the penis: a series of 29 cases with predilection for ductal adenocarcinoma.

Twenty-nine men with metastatic prostate adenocarcinoma to the penis were identified at our institution between 1993 and 2013. Of the 29 patients, 19 had a prior history of adenocarcinoma of the prostate, and 8 of those had ductal features in the primary lesion. Sixteen of 29 revealed ductal features in the metastasis. Seven of the 8 cases with ductal features in the primary had ductal features in the penile metastasis. Seven penile metastases were proven to be of prostatic origin solely by immunohistochemistry. Three cases were originally misdiagnosed as urothelial carcinoma upon review of the penile lesion. Other variant morphologies in the metastases included sarcomatoid carcinoma, small cell carcinoma, and adenosquamous carcinoma. In summary, prostate carcinoma involving the penis displays ductal features considerably more often than prostate cancer in general. Features that can cause difficulty in recognizing metastatic prostate adenocarcinoma to the penis include the unusual anatomic site for prostate cancer, poor differentiation, an increased prevalence of variant morphology, a long interval from the primary lesion, and, in some cases, no documented history of a primary prostatic lesion. Immunohistochemical analysis should be performed to rule out prostate carcinoma in penile/penile urethral tumors with morphology that differs from typical squamous or urothelial carcinoma. Even in the setting of metastatic disease, there is a critical need for an accurate diagnosis so that the appropriate therapy can be initiated, symptomatic relief can be provided, and long-term survival achieved in some cases, while at the same time avoiding penectomy for a misdiagnosis of a primary penile cancer.