Invasive Renal Angiomyolipoma With Cytologic Atypia.

Renal angiomyolipoma (AML) is a benign neoplasm of the kidney arising sporadically in an idiopathic manner, or syndromically as a component of tuberous sclerosis complex. Although the classic AML has no malignant potential, and is the most common mesenchymal tumor of the kidney, variant AML cases with epithelioid morphology have demonstrated aggressive or invasive behavior. Classic AML, on the other hand, can occasionally display focal histology concerning for sarcomatous transformation, but in the absence of invasive features, it is easy to distinguish from a malignancy. In this article, we describe a remarkable case of classic AML that harbored areas histologically mimicking liposarcoma and invaded into the renal vein and extended up to inferior vena cava, thereby presenting a unique diagnostic conundrum. However, the tumor is negative for a CPM gene amplification, arguing against a liposarcomatous transformation. In addition, the patient does not have any sign of recurrence and metastasis clinically after 2 years of follow-up, also favoring a benign diagnosis of this tumor.