Test of recurrence after experimental radiation therapy of chemically induced autochthonous tumors in mosaic mice.

True recurrence was distinguished from induction of new second tumors after experimental radiation therapy using monoclonal tumors produced in the mosaic cell background of mice. The mice were C3H/He females heterozygous at the X-chromosome-linked locus of phosphoglycerate kinase (PGK) and consisted of two types (A and B) of somatic cells by inactivation of one of X-chromosomes. Sarcomas and carcinomas with a single PGK phenotype were produced by subcutaneous injection of 3-methylcholanthrene (MCA) into the groin of the mice, and locally and singly irradiated with 4-6.5 Krad of X rays generated by a 6 Mev linear accelerator, when they were 8-10 mm in diameter. Of 69 mice irradiated, 17 were available for comparison of the PGK and histological types of primary and recurrent tumors. Of these, 10 recurrent tumors with A-type PGK and 3 with B-type PGK exhibited the same PGK type as that of primary tumors, while one was distinguishable histologically. Only one recurrent tumor was of the opposite PGK and a different histological type from the primary tumor. Considering the probability of new tumor formation among A----A recurrent tumors, it was calculated that 79% (11/14) of the tumors that reappeared in the irradiated area were actually true recurrent tumors. Autochthonous tumors may be important in testing therapeutic methods.