We report 3 recent cases of
angiomyolipoma of the kidney. Although generally regarded as a
benign neoplasm,
angiomyolipoma rarely behaves in an aggressive manner, producing complicated clinical courses leading to
metastasis and death. The presence of epithelioid elements within the
tumor can result in difficulty differentiating benign from malignant
angiomyolipoma and differentiating this
tumor from
renal adenocarcinoma. The presence of lymph node involvement can cause difficulty in differentiating multicentric disease in lymph nodes from
metastasis to lymph nodes. The presence of cytologic abnormalities in the primary
tumor can result in difficulty in differentiating atypia in benign
angiomyolipoma from malignant sarcomatous transformation of a benign lesion. The 3 cases reported show many of these problems. Criteria for predicting
malignancy in epithelioid
tumors and sarcomatous transformation are not well recognized because of the rarity of this entity. The typical immunophenotype of all types of
angiomyolipoma (
cytokeratin-negative and melanomarkers-positive) is very useful in diagnosis but does not help in the differentiation from
renal adenocarcinoma at frozen section. We report the empiric use of Ki67 and p53 in these cases as adjuncts to clinical and histologic assessment in predicting behavior. High Ki67 expression was a feature of malignant epithelioid
angiomyolipoma. Low levels of p53 expression were seen in the
angiomyolipoma with sarcomatous transformation. Benign
angiomyolipomas were consistently negative for both Ki67 and p53.