Primary renal myxofibrosarcoma.

Kidney sarcomas are rare, representing only 1% of malignant renal tumors. We herein report the case of a 70-year-old woman that was admitted for an episode of confusion in relation to hypertensive encephalopathy. Imaging investigations revealed a large mass in the right kidney with extension to the renal hilum. The patient underwent right open radical nephrectomy. The histopathologic study disclosed a 15-cm, myxoid and cellular, pleomorphic tumor with elongated, curvilinear, thin-walled vessels, and focal necrosis that involved the upper and middle segments of the kidney. Immunohistochemically, the tumor cells showed strong positivity for vimentin, bcl2 protein (nuclear staining pattern), CD34, CD99, and alpha-methylacyl coenzyme A racemase. The tumor was diagnosed as myxofibrosarcoma (MFS) grade 2 according to the FNCLCC system. To the best of our knowledge, this is the first report of an MFS arising from the kidney. Thus, MFS is an uncommon soft tissue tumor that can exceptionally arise from the kidney. The differential diagnosis with other myxoid tumors is of vital importance because it includes lesions with subtle differences and extremely variable biological behavior. Radical surgery is the treatment of choice. Long-term follow-up is recommended because of the tumor's capability for local recurrence and distant metastasis.