A lung colony clonogenic cell assay for human malignant melanoma in immune-suppressed mice and its use to determine chemosensitivity, radiosensitivity and the relationship between tumour size and response to therapy.

A lung colony assay for clonogenic cells of human tumours in immune-suppressed mice is presented. The assay was used to determine the chemosensitivity of two malignant melanomas. One tumour reproduced the spectrum of chemosensitivity associated clinically with three cytotoxic agents. The other melanoma reproduced the chemosensitivity demonstrated in the patient from whom the tumour was biopsied. The importance of tumour size as a determinant of response to melphalan was investigated and the clonogenic cell survival in smaller tumours was found to be slightly but significantly lower than in larger tumours. An invesitgation of the importance of size as a determinant of response to radiotherapy demonstrated that 0.5-mm diameter tumour nodules were significantly more sensitive to irradiation than 2-cm diameter nodules. The hypoxic fraction of the larger tumours was 65 per cent, which is higher than that reported for experimental animal tumours or a human pancreatic tumour. This could be a factor in the clinical radioresistance of malignant melanoma.