In an observational, correlational study published in 1975 by Carroll, K. K. and Khor, H. T., they compared breast cancer rates with dietary fat intake for many countries and found that the countries with the highest incidents of breast cancer also have the highest intake of dietary fat. A high dietary fat intake is usually associated with a high animal protein intake, suggesting a correlation between animal protein and breast cancer.
In a major review of the world's literature on diet and cancer published in 1997 by the American Institute for Cancer Research/World Cancer Research Fund, it was observed that breast cancer risk increases with greater body weight, higher percent body fat, and more meat consumption accompanied by less grain and legume consumption.
Findings from The China Project published in 1992 by Campbell, T. C. et. al. found that nutritional factors from animal foods are associated with chronic diseases, while nutritional factors associated with plant foods showed the reverse. These findings for a unique human population were very consistent with laboratory findings.
My take on all this: eat more fresh vegetables, fruit, whole grains, nuts, beans, and legumes, and less meat, fish, and dairy, including eggs.