| Abstract: | In order to clarify the mode of action (tumor cell death) of tamoxifen in treatment for estrogen receptor (ER) negative malignant melanoma, we administered the usual adult dose (20 mg/day) or a low dose, 1/4 of the usual dose (5 mg/day), of tamoxifen for 2 months to 2 male patients and investigated ultrastructural changes in their melanoma cells from metastatic lesions before and after the treatment. After the 2-month adminisration, metastatic nodules in both patients were reduced in size by approximately 50%. Histologically, their reduced nodules presented coagulation necrosis around the blood vessels. Electron microscopy of the necrosis revealed that melanoma cells were degenerated and disappeared; numerous aggregated melanosomes, free melanosomes, granular endoplasmic reticula, and lysosomes were present in the extracellular matrix and in the space between collagen fibers. The remaining melanoma cells had swollen cytoplasm and mitochondria with vacuolar changes. Cristae of mitochondria had disappeared. There was no infiltration of lymphocytes or histiocytes into the nodules. The organic changes of necrosis lesions were not observed. Because our two patients were ER negative, these effects of tamoxifen could be attributable to an action not mediated by ER. |
