Estrual cycle periodicity in hormone-independent tumor-bearing mice.

The periodicity of the estrual cycle in mice was studied by vaginal cytology during the growth of a hormone-independent mammary adenocarcinoma. A direct relationship between age progression and lengthening of estrual cycle was observed in control mice but not in tumor-bearing mice of the same age. These results suggest that hormone regulation of the estrual cycle may be affected in tumor-bearing hosts.