Soluble low-molecular-mass tumor-associated proteins promote the suppression of mammary tumors by cyclophosphamide

This study examined whether the soluble tumor-associated-antigens (TAA), of 66 kDa and 51 kDa, could promote suppression by anticancer drugs of chemic ally-induced mammary tumorigenesis. Dimethylbenzanthracene (DMBA, 10 mg/rat , twice) was used to induce mammary tumors. Then, for nine more weeks, the preparation of TAA and cyclophosphamide (CPA), alone or in combination with TAA, were administered in weekly doses. Twenty weeks after DMBA exposure, the mammary tumor yield was 2.4, 2.8 and 2.9 in the experimental groups com pared to 3.5 in the controls. Seventy-five percent of the rats in the contr ol group, but only 37% of TAA, 50% of the CPA, and 30% of the CPA and TAA t reated animals had malignant tumors. In the experimental groups, 6.5%, 25% and 38%, respectively, of the tumors regressed, compared to 3% in controls. In the groups receiving CPA or TAA, regression was observed in the fifth w eek of treatment, and in the group receiving combined treatment, already in the first week. The size of the tumors in control rats increased during th e last 10 weeks 3.6 times, in the CPA treated rats 1.15 times, but in those receiving CPA plus TAA it decreased by 0.7 times. The results of our exper iment demonstrated that TAA have distinct tumor-suppressive properties, and can enhance the anticancer effects of CPA.