Leiomyosarcoma is the most common primary renal sarcoma. Most patients are beyond 40 years of age; M:F = 2:1. The tumor is composed of intersecting fascicles of smooth muscle cells.

• 平滑肌肉瘤是最常见的肾原发性肉瘤。绝大多数病人超过40岁，男：女＝2：1。肿瘤是由纵横交错的平滑肌束组成。