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Repair of Potentially Lethal Damage in Vivo in Solid Tumor Cells After X-Irradiation¹

Department of Radiology, Stanford University School of Medicine, Stanford, California 94305 [G. M. H., S. R., R. F. K., L. F. G.], and Institut Gustave-Roussy, 16 bis, Avenue Paul-Vaillant-Couturier, 94 Villejuif (Val-de-Marne), [E. F.] France

The survival of cells from two transplantable murine tumors (NCTC 2472 fibrosarcoma and EMT6 mammary sarcoma), X-irradiated in vivo, was assayed by determining the clonogenicity of the cells in vitro. Cells from tumors kept in situ 6 or 24 hr after irradiation had higher survival than cells from tumors excised immediately after irradiation. This increase in survival was done dependent and had a time constant of 2 to 4 hr. Similarity to earlier in vitro findings leads us to interpret the enhanced survival as a manifestation of repair of potentially lethal damage by cells remaining in a growth-inhibited state after irradiation.

¹ This work was supported by INSERM (France) and by USPHS Grants CA-10372 and CA-04542.

² Holder of a Dernham Senior Fellowship in Oncology from the American Cancer Society (California Division).

Received 6/20/73. Accepted 11/ 9/73.