The criteria for malignancy in smooth muscle neoplasms of kidney are not clearly defined.Large size, necrosis, nuclear pleomorphism, increased mitotic actiity faor malignancy.

• 肾脏恶性平滑肌肿瘤的诊断标准较难设定，如瘤体较大、坏死、胞核多形性、有丝分裂活性增强，则应考虑为恶性。