Renal angiomyolipomas and HMB-45 reactivity

Renal angiomyolipomas (RAML) are mesenchymal hamartomas composed of varying amounts of blood vessels, smooth muscle, adipose tissue, and supporting connective tissue. Although most of these tumors are easy to recognize, some show unusual histologic features and may pose a diagnostic dilemma. Recent reports indicate that RAML are immunoreactive for HMB-45 antibody, which is directed against a premelanomasome-associated glycoprotein and is thought to be specific for melanocytic differentiation.

To determine whether HMB-45 reactivity would differentiate RAML from other renal tumors, the authors immunostained 72 primary renal tumors, including 19 angiomyolipomas and 2 retroperitoneal liposarcomas extending into the kidney, with HMB-45 monoclonal antibody. Also, the immunohistochemical profile of 19 renal angiomyolipomas was investigated using a broad panel of immunostains, including cytokeratin (AE1/AE3), epithelial membrane antigen, vimentin, smooth muscle actin (SMA), desmin, muscle-specific actin (MSA), S-100 protein, and neuron-specific enolase (NSE).

All tumors except RAML were negative for HMB-45 antibody. HMB-45 immunoreactivity was present in 17 of 19 RAML. Seventeen of 19 were positive for SMA and MSA (HHF 35), 8 for desmin, 17 for vimentin, and 9 for NSE.

Based on this study, it was concluded that, along with SMA and MSA, HMB-45 reactivity is a useful tool to distinguish RAML, especially those with unusual morphological features, from other primary renal neoplasms, including liposarcomas that extend into the kidney.