In a long-term study of 2 sublines of the Ehrlich ascites tumor, one maintained in male mice and the other in females, significantly less growth occurred with the tumor from male donors when tested in mice of either sex. In addition, significantly less growth occurred in male than in female mice inoculated with tumor from either subline; the 2 effects, due to the sex of the donor and to the sex of the recipient, could be clearly distinguished. Despite the differences in tumor growth, however, the only significant prolongation of survival in male mice was found in those inoculated with 105 cells and not in those inoculated with 106 or 107 cells. Subcutaneous tumor inoculation 1 week prior to intraperitoneal injection resulted in prolonged survival in 55% of treated mice, but this effect was not related to the subline of the tumor used. A change in the modal chromosome number, from 44 to 45 per cell, occurred in both sublines; this was more marked in the subline maintained in males than it was in the subline in females. In addition, the number of metacentric marker chromosomes increased from 1 to 2 per cell in almost all cells of each subline.

The results suggest that differences between the growth of tumor maintained in male or female mice were due to the selection, in male animals, of cells with a decreased growth potential. Such a selection may have been related to the relatively poor tumor growth found in male mice inoculated from either subline. The relevance of these results to experimental tumor studies is discussed.

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