UC Irvine

The distinction between metastatic amelanotic melanoma and a poorly differentiated carcinoma is often difficult. With the use of the ultrastructural L-DOPA reaction as a tool for measuring tyrosinase activity within vesicular and cisternal organelles, cells containing melanin can be identified. Our study identified a tumor which was classified by light microscopy as an undifferentiated carcinoma and by electron microscopy as an undifferentiated neoplasm. Nine parameters were evaluated: a nude mouse xenograft, the patient's tumor cells in agar with and without L-DOPA treatment, and single cell suspensions of the patient's tumor cells with and without L-DOPA treatment. As controls, cells from Cloudman S91 (CCL) 53.1 melanoma, grown into colonies in agar with and without L-DOPA treatment and in single cell suspensions with and without L-DOPA treatment, were evaluated. The xenograft demonstrates no melanosomes. Cells in single cell suspensions with L-DOPA treatment and patient cells grown into colonies in agar with and without L-DOPA treatment contain granular dense bodies within the cytoplasm, suggestive of melanosomes. Premelanosomes (Stage II), Golgi, and Golgi-associated smooth endoplasmic reticulum contain DOPA-positive reaction product when cultured in the agar assay. A DOPA-positive reaction is also noted in the Golgi-associated smooth endoplasmic reticulum of the single cell suspensions. The CCL line demonstrates premelanosomes in all cases. These. findings unequivocally identify the tumor as amelanotic melanoma and indicate that identification of DOPA-positive cells grown into colonies in agar are essential for diagnosis. These parameters may be applied to ambiguous cases of malignancy for which amelanotic melanoma is suspected. (Supported in part by grants from NIH (T32 CA09213 to B.P.) and ACS (PDT-184 to F.L.M. and PDT-205 to M.J.C.H.)