Radiosensitivity of Lymph Node Metastases versus Initial Subcutaneous Tumors in Nude Mice

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Abstract
The in vivo and in vitro radiosensitivity of [mouse mammary tumor] EMT6 tumor cells growing s.c. and metastasizing to the regional lymph nodes was studied in congenitally athymic nude mice. The fraction of hypoxic cells was determined using an in vitro colony method to assay cell survival after irradiation of both air-breathing and N2-asphyxiated animals. In air-breathing animals, lymph node metastases contained a significantly higher fraction of hypoxic cells than s.c. tumors of the same size (61 and 36%, respectively). Survival curves did not differ under hypoxic conditions (N2-asphyxiated animals). Likewise, survival curves of cells extracted from tumors at both sites and irradiated in vitro were identical.