Primary leiomyosarcoma of the kidney.

Primary leiomyosarcoma of the kidney is a rare tumor with an aggressive behaviour. A 55-year-old woman presented with a left sided abdominal mass in our outpatient department. Radiologic investigations revealed the mass to be renal in origin with colonic adhesions for which radical nephrectomy and hemicolectomy were done. The tumor completely appeared to replace the left kidney and had a whorled character focally on cut section. Microscopically, spindle cells having malignant features with cigar shaped nuclei were seen. The smooth muscle origin of the cells was confirmed by immunohistochemical positivity for smooth muscle actin. Sarcomatoid variant of the renal cell carcinoma was ruled out as the tumor was negative for cytokeratin. Tumors with spindle cell morphology in the kidney should not always be taken for a sarcomatoid variant of renal cell carcinoma and should be investigated thoroughly.