Cytologic features of Harding-Passey melanoma following different regimes of colchicine treatment.

Ultrastructural observations were undertaken on Harding-Passey melanomas in control tumors and in tumors treated with different regimens of colchicine. The treated tumor was made up of pleomorphic cells containing tubulovesicular mitochondria, ribosomes, and rough endoplasmic reticulum. Tumor-bearing mice in Experiment A received a single regimen of colchicine, 0.5 mg/kg/day of 7 days. The treated tumor was subsequently passed through five transplantations in mice. Tumor-bearing mice in Experiment B received colchicine treatment of 0.5 mg/kg/day for 7 days followed by passage through five transplantations. In addition, the mice carrying the tumor received the same colchicine treatment during the second and fourth transplantations. Colchicine treatment resulted in tumor cells of Experiments A and B developing microfilaments, margination of melanin granules, and junctional complexes, considered to be evidence of altered morphologic differentiation in melanocytes. The effects persisted for 10 weeks throughout the five transplantations. The features were more striking in Experiment B animals receiving intermittent therapy.