Epidermotropic Metastatic Prostate Adenocarcinoma With Florid Squamous Transformation/Differentiation and Associated Acantholysis. An Unusual Clinicopathologic Entity.

Prostate adenocarcinoma is the most common carcinoma in men. Cutaneous metastasis of prostate adenocarcinoma, however, is rare, accounting for less than 1% of metastatic cutaneous carcinomas. This cutaneous spread most often occurs in the inguinal area and the penis, followed by the abdomen, head and neck, chest, extremities, and back. Metastatic prostate adenocarcinoma generally has a poor prognosis, emphasizing the importance of timely identification. We report a patient with an unusual clinicopathologic presentation of metastatic prostate adenocarcinoma manifesting as a scaly plaque on the left shin. This lesion was histopathologically characterized by marked epidermotropism, squamous differentiation, and acantholytic features, with a negative reaction to prostate-specific antigen and prostatic acid phosphatase immunostains. When evaluating metastatic cutaneous carcinomas displaying epidermotropism and squamoid appearances or squamous differentiation, it is essential to maintain a high index of suspicion and inquire about a history of prostate carcinoma. This history is especially relevant if hormonal therapy was utilized as part of the patient's management.