Estradiol is trophic for colon cancer in mice: effect on ornithine decarboxylase and c-myc messenger RNA.

The mitogenic role of estradiol on the growth of colon cancer was examined in mice. Sham-operated or ovariectomized mice were injected with cancer cells and received estradiol treatment. Tumor growth was noted: tumor weights were higher in female than male mice. The growth of the tumors was least in ovariectomized mice and highest in estradiol-treated ovariectomized mice. Tumor messenger RNA (mRNA) levels for ornithine decarboxylase (ODC) and proto-oncogenes c-myc, c-fos, and H-ras were examined. Two transcripts (2.2 and 2.7 kilobase pairs) of ODC were observed. The steady-state mRNA levels for ODC paralleled the changes observed in the weight of the tumors in all groups of animals. Less dramatic changes were observed in c-myc mRNA levels. No significant differences were observed in the mRNA levels for H-ras and c-fos. It thus appears likely that an increase in the ODC mRNA levels and, to a lesser extent, an increase in c-myc mRNA levels may be some of the important mechanisms by which estradiol mediates its growth effects on colon cancer cells in vivo.