Renal angiomyolipoma: Clinico-pathologic study of 17 cases with emphasis on the epithelioid histology and p53 gene abnormalities.

BACKGROUND: Epithelioid angiomyolipoma (EAML) is a rare potentially malignant variant of renal angiomyolipoma (RAML). This study aims to determine whether RAML clinico-pathologic and molecular features (i.e. p53 gene abnormalities) differ significantly with regards to its histologic variant or to the presence of an epithelioid component within it. METHODS: Consecutively resected RAML were reviewed, tumours comprising at least 80% of epithelioid cells were considered as EAML according to the 2016 World Health Organization classification of tumours of the kidney. P53 gene abnormalities were investigated using both immunohistochemical and molecular analysis. RESULTS: A total of 3 EAML among 17 RAML were identified, accounting for 3.9% of the total AML cases. Fatty aspect on imaging was more observed within tumours devoid of an epithelioid component. EAML showed a higher mitotic rate and a stronger p53 staining, no renal poles involvement and was not treated by nephron sparing surgeries. RAML comprising an epithelioid component demonstrated severer nuclear atypia as well as stronger p53 staining. P53 gene sequencing revealed a missense mutation (c.747G > C) in one classic AML harbouring a strong labelling with p53. CONCLUSIONS: Strong p53 staining in a RAML, even in the absence of gene mutation, may suggest the presence of an epithelioid component or of a truly EAML. To the best of our knowledge, c.747G > C p53 gene mutation is being reported for the first time in a RAML, although its role in AML pathogenesis is still unknown.