Malignant and benign renal perivascular epithelioid cell tumors: A comparison and review of the literature

While angiomyolipoma (AML) is a fairly common urological tumor, malignant AMLs rarely appear in clinical practice. As such, currently there exists little knowledge of malignant AMLs. This article discusses the differences between benign and malignant AMLs. Besides, we report two cases of AML with opposite nature in Nan Fang Hospital from 2010 to 2016 and discuss the key features based on clinical manifestation, pathogenesis, radiology, and pathology. Case 1 was a 44-year-old, asymptomatic female presenting with a mass measuring 4 cm in diameter in the inferior pole of the left kidney. Case 2 was a 23-year-old female presenting with abdominal pain for 1 month, a mass measuring 5.5 cm in diameter in the superior pole of the right kidney, regional infiltration, and enlarged retroperitoneal lymph nodes. Based on Folpe's grading scheme, the Case 1 tumor was benign due to the absence of criteria mentioned in the grade and the Case 2 tumor was malignant due to a tumor size >5 cm, infiltrative growth pattern, necrosis, high nuclear grade, and subsequent aggressive clinical behavior. Each patient underwent surgical resection: Case 1 demonstrated no evidence of recurrence at the 9-month follow-up; however, Case 2 died 3 years postoperation due to tumor recurrence. These results demonstrate that malignant AML has aggressive biological activities and almost always associates with unfavorable prognoses. Therefore, a strict follow-up should be given to “uncertain malignant potential” patients, and surgical resection should be performed.