ANGIOMYOLIPOMA OF THE KIDNEY - IMMUNOREACTIVITY WITH HMB-45 - LIGHT-MICROSCOPIC AND ELECTRON-MICROSCOPIC FINDINGS

Immunoreactivity with HMB-45 has recently been described in renal angi omyolipoma, a tumour of smooth muscle cells. HMB-45 is a monoclonal an tibody that reacts specifically with melanosomes. In order to determin e whether the tumour cells contain melanosomes and synthesize melanin, seven tumours were studied by light microscopy and immunohistochemica lly with the antibodies HMB-45, KP1 (CD68), PG-M1 (CD68), Ki-M1P, anti -lysozyme, antismooth-muscle actin, anti-vimentin, anti-S100 protein a nd KL1 (anti-keratin). Two tumours were also studied by electronmicros copy and one by immuno-electronmicroscopy. Histochemical investigation for dopa oxidase was performed on cryostat sections. The tumours cont ained varying numbers of HMB-45-positive muscle cells. Reactivity was noted in lysosomal granules and rough endoplasmic reticulum. Typical p remelanosomes were found in the tumour cells by electronmicroscopy. Gr oups of tumour cells stained for dopa oxidase. The tumour cells were n ot reactive for lysozyme, but reacted with KP1, PG-M1 and Ki-M1P. Immu no-electronmicrosopy showed that reactivity for KP1 was located within lysosomal granules. The findings show that the tumour cells of renal angiomyolipoma contain premelanosomes and that they are able to synthe size melanin, because they contain dopa oxidase. Immunoreactivity with KP1, PG-M1 and Ki-M1P can be attributed, in the absence of staining f or lysozyme, to the large number of lysosomal granules. The tumour cel ls were not found to be related to macrophages or myeloid cells.