Spontaneous mammary tumors: decrease of incidence in mice infected with an enzyme-elevating virus.

Mice infected with a virus which causes increased activity of lactate dehydrogenase, and of other enzymes in blood plasma, had a significantly lower incidence of spontaneous mammary carcinoma than did controls. When the experiment was terminated at 18 months, the incidence of mammary tumors in controls was 90 percent, and in infected mice, 53 percent.