Model of mouse mammary gland hyperproliferation and hyperplasia induced by a western-style diet.

Mammary glands of female C57BL/6J mice were analyzed after they were fed a Western-style diet or control AIN-76A diet. The Western-style diet contained several risk factors found in human diets in geographic regions having increased risk for breast cancer: high fat and phosphate and low calcium and vitamin D. After they were fed these diets for 8, 14, and 20 weeks, mice were sacrificed, and mammary glands were removed for morphometric and radioautographic measurements. Although after the animals were fed the Western-style diet for 8 weeks the number of terminal ducts per mouse mammary gland (NTDMG) was similar in the Western-style and control diet groups, after they were fed the Western-style diet for 14 weeks (p < 0.05) and 20 weeks (p < 0.01) the NTDMG significantly increased compared with the control group. Moreover, there was a significant increase (p < 0.01) in the tritiated thymidine labeling index of mammary terminal ductal epithelial cells after 14 and 20 weeks of Western-style diet administration. Thus the Western-style diet induced increased epithelial cell proliferation and increased NTDMG in female mice when fed during young adult growth and development. The findings raise the possibility that the ingestion of a diet with Western-style fat and phosphate content and with low calcium and vitamin D may induce similar changes during the early development of the human mammary gland.