Radiosensitivity of the cells of an established human melanoma cell line and the parent melanoma xenograft.

Survival curves of cells from a human melanoma xenograft (E.F.) and a cell line (FME) established from this xenograft were determined. The cells of the established line were harvested from exponentially growing cultures, plateau phase cultures or solid tumours in athymic mice (FME-X) before irradiation. During irradiation the cells were kept suspended in culture medium. The colony forming ability of the cells was assayed in soft agar. The Do-value was significantly higher for the parent xenograft than for the established line, whether grown in vitro or in vivo (p less than 0.0001). In addition, the Dq-value was significantly lower for the xenograft than for exponentially growing cultures of the established line (p less than 0.05). Thus the radiation response of the cells of the established line was not representative for that of the cells from the parent xenograft. It is concluded that survival curves for established cell lines should be used with great caution in attempts to predict the radiocurability of human tumours of corresponding histological type.