Expression of melanocyte-associated markers gp-100 and Melan-A/MART-1 in angiomyolipomas. An immunohistochemical and rt-PCR analysis.

Angiomyolipomas are tumours of uncertain histogenesis, most often occurring in association with the kidney. A characteristic finding is their reactivity with HMB-45, a monoclonal antibody to the melanocyte-associated antigen gp-100. We tested 18 angiomyolipomas for their reactivity with A103, a monoclonal antibody to Melan-A (MART-1), another melanocyte-associated marker, and compared it with HMB-45. All cases were positive with both antibodies, yet most cases showed a more homogeneous staining pattern with A103. Normal kidney was immunohistochemically negative for both antibodies. We also performed RT-PCR assays for gp-100 and Melan-A in 4 of the 18 angiomyolipoma samples and in three normal kidney samples. All 4 angiomyolipoma specimens revealed mRNA for both melanocyte differentiation markers. gp-100 mRNA was found in the samples of normal kidney, but Melan-A mRNA was not. Our study shows that angiomyolipomas express the melanocyte-associated antigens Melan-A and gp-100 at the protein and at the mRNA level, suggesting a true expression of these antigens rather than cross-reacting epitopes. Based on the mRNA expression pattern, immunohistochemical analysis is the preferred method for the detection of gp-100, while Melan-A can be used at the protein and mRNA levels. Our study demonstrates that A103 is a useful marker for the diagnosis of angiomyolipomas.