HMB-45 and tuberin in hamartomas associated with tuberous sclerosis

Tuberous sclerosis (TSC) is an autosomal dominant condition characterized by various hamartomas. To assess whether these hamartomas have common features, we immunohistochemically analyzed an autopsy case of TSC with subependymal giant cell astrocytoma, hamartomatous lymphangioleiomyomatosis in the lungs and uterus, and angiomyolipomas in the liver, bilateral kidneys, parametrium, and a lymph node, using the specific antibodies for tuberin (the gene product of TSC2) and HMB-45 (a monoclonal antibody specific for human melanoma). Tuberin was ubiquitously expressed in the normal organs. It was negative or very weakly expressed in the hamartomas. In contrast, HMB-45 was commonly observed in the hamartomas except for the lesions in the brain. The subependymal giant cell astrocytoma was composed of cells immunoreactive for synaptophysin, neurofilament protein, glial fibrillary acidic protein, and S-100 protein but negative for HMB-45 and tuberin. The suppression of tuberin in the brain tumor and visceral hamartomas and an abnormal expression of HMB-45 in the visceral hamartomas were observed. We conclude that the hamartomas associated with TSC have common phenotypic and etiologic expressions and that the genes responsible for both tuberin and the antigen recognized by HMB-45 have important roles in the pathogenesis of these hamartomas.