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HMB-45 monoclonal antibody is thought to be highly specific for melanocytic proliferations. In a recent study of two cases of hepatic and one case of renal angiomyolipoma, strong staining of lesional cells with this antibody was unexpectedly encountered. In follow-up evaluation, the authors studied 51 additional soft tissue, renal, and brain tumors and tumor-like processes, with emphasis on those with prominent vascular, myogenous, and fatty components or those known to be associated with tuberous sclerosis. Varying degrees of staining with HMB-45 were seen in 17 of the lesions tested. Strong staining with HMB-45 was demonstrated in four renal angiomyolipomas. Clearly positive results were also obtained in three other processes associated with the tuberous sclerosis complex, including two cardiac rhabdomyomas and one tuberous lesion of the brain. Weak staining of several other mesenchymal and neural lesions was also observed. Electron microscopic studies showed a spectrum of granules within angiomyolipoma, some of which resembled melanosomes and others renin granules. Similar granules were observed in cardiac rhabdomyoma, cerebral tuberous lesions, and in subependymal giant cell astrocytoma. We propose that tuberous sclerosis-associated tumors and tumor-like processes are interrelated, and that these and perhaps other mesenchymal proliferations may share components previously believed to be unique to melanocytic lesions. Int J Surg Pathol 1 (3) :191-198, 1994

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