Sarcomatoid carcinoma after radiation treatment of prostatic adenocarcinoma.

We report 2 patients with conventional prostatic adenocarcinoma who developed sarcomatoid carcinoma of probable prostatic origin 6 and 2.5 years after radiation treatment (seed implantation and external beam). Our cases had histologic features consistent with those cases previously reported in the literature. The tumors consisted of spindle cells with large hyperchromatic nuclei and a pattern mimicking a sarcoma. Immunohistochemical studies showed the tumors to be weakly positive for EMA, CK7, and vimentin. Ki67 staining showed positivity in more than 50% of tumor cells. The tumors also stained diffusely positive for p53 and p63. PSA and PAP were negative. Clinically, the sarcomatoid carcinomas appeared to be of prostatic origin. The pathogenesis of the tumors is still uncertain but most likely represent a radiation-induced dedifferentiation of prostatic adenocarcinoma.