Solid Sarcoma 180 implanted s.c. into Swiss albino mice regularly produces a tumor that spontaneously regresses in a low proportion of hosts. A statistically significant increase in the regression ratio has been observed following therapy with basidiomycete polysaccharide, with polyinosinic-polycytidylic acid at a high dose, and with zymosan. The regression ratio was not increased by Protodyne or chlorphenesin.

In several strains of inbred mice that carry the H-2d allele (homozygous or heterozygous), in contrast to Swiss mice, no spontaneous regression of Sarcoma 180 is observed, nor was regression induced in these mice by the chemicals that enhanced the ratio in Swiss mice. In the strains of mice lacking the H-2d that were tested, various regression ratios up to 100% were observed.

The ascitic form implanted s.c. produced tumors that regressed in the various strains of mice in ratios similar to those observed after solid-tumor implantation. In contrast, the ascitic form inoculated i.p. produced ascites from which mice uniformly died within 10 to 12 days, regardless of the genotype of the host.

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Supported in part by Grant CA-08748 from the National Cancer Institute, USPHS, and from the Elsa U. Pardee Foundation.

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