Higher magnification view of the spindle cell proliferation in the classic form of mesoblastic nephroma. The cells lack cytologic atypia but may show increased mitotic activity. Hemorrhage and necrosis are not seen. Most cases are cured by nephrectomy alone and do not require chemotherapy or radiation. Less than 10% of cases may recur in the retroperitoneum and follow an aggressive clinical course. Rare cases with distant metastases to the lungs and brain have been reported.