Pleomorphic leiomyosarcoma with a dedifferentiation-like appearance in the kidney: case report and literature review.

Although primary leiomyosarcoma of the kidney is extremely rare, it is the most common sarcoma of the kidney. Leiomyosarcoma with a large pleomorphic component is designated as pleomorphic leiomyosarcoma. The pleomorphic component is usually similar to undifferentiated high-grade pleomorphic sarcoma, although it variably expresses smooth muscle markers on immunohistochemistry. In the few reported cases of pleomorphic leiomyosarcoma of the kidney, cases with the pleomorphic component showing distinct nodularity similar to dedifferentiated leiomyosarcoma have not been described, to the best of our knowledge. Herein, we present a case of a 49-year-old woman with pleomorphic leiomyosarcoma in the kidney showing distinct nodularity of smooth muscle marker-expressing pleomorphic cells within a background of classic leiomyosarcoma. Along with the classification as a pleomorphic leiomyosarcoma, suggesting aggressive clinical behavior, the renal origin itself might also be a predictor of poor prognosis, as shown in a previous study. This case also involved concomitant distant metastases, already present during the initial detection of the renal tumor.