Milk Inhibits the Regression of 7,12-Dimethylbenz(a)anthracene-Induced Mammary Tumors in Ovariectomized Rats

Abstract

Epidemiological studies have yielded inconsistent results regarding the relation between the milk consumption and breast cancer risk. In this study, rats were induced mammary tumors by 7,12-dimethylbenz(a)anthracene. When tumors developed to acceptable levels, rats were placed into 1 of 3 treatment groups. Those in the negative control group and the milk group were ovariectomized, whereas those in the positive control group were sham operated. After grouping, tumor incidence remained 100%, and tumor number and volume increased in the positive control group. However, tumors in the 2 ovariectomized groups regressed. Compared with the negative control group, tumor incidence and tumor number and volume per rat in the milk group became significantly higher from Week 6 and Week 4, respectively. Insulin-like growth factor-I levels were borderline significantly higher in the milk group than in the negative control group at autopsy. Although plasma 17β-estradiol levels did not differ significantly, estrogenicity was found in the milk group because uterine weight was significantly heavier in the milk group than in the negative control group. In conclusion, commercial milk inhibited the regression of carcinogen-induced mammary tumors in ovariectomized rats.

ACKNOWLEDGMENTS

This study was supported in part by grants from National Natural Science Foundation of China, 30771808, and from Japan Society for the Promotion of Science, P05504. We thank Dr. Yue-Ping Shen for the assistance of statistical analysis.

Notes

^a Significant difference from the positive control group (P < 0.05).

^b Significant difference from the negative control group (P < 0.05).

^a n = 12. Abbreviation is as follows: IGF-I, insulin-like growth factor-I.

^b Significant difference from the positive control group (P < 0.05).

^c Significant difference from the negative control group (P < 0.05).