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The Effect of Pregnancy on Sarcoma 180 in Albino Swiss Mice^*

( Cancer Research and Cancer Control Unit, Tufts College Medical School, Boston, Mass.)

In four experiments with 281 female albino Swiss mice, it was observed that pregnancy effected from 68 to 100 per cent complete regressions of Sarcoma 180. The higher rates of regression occurred in fertile females, mated from 4 to 16 days after transplantation of the tumor.

Regressions also occurred in from 28 to 31 per cent of sterile females, mated from 4 to 16 days after and from 6 to 12 days before transplantation of the tumor. The percentage of regressions was 2–3 times greater than that observed in the nonmated virgin controls. The progression of tumors resulting in death of the nonpregnant animal was greatest (94 per cent) when the tumor was transplanted within 24 hours before sterile mating.

It is concluded that pregnancy may present conditions unfavorable to tumor growth and that sterile mating (not coincident with inception of tumor) may also change the receptivity of the host.

^* This study has been supported by grants-in-aid from the American Cancer Society, Inc., Massachusetts Division; and by an institutional grant from the American Cancer Society, Inc., New York.

Received 2/ 4/54.