Differences in breast cancer mortality worldwide: unsolved problems.

Breast cancer mortality remains a major cause of female mortality. Between 1970 and 2000 both important increases and decreases in breast cancer mortality rates occurred. Large differences in breast cancer mortality exist among countries worldwide. Contradictory findings concerning the role of lifestyle, especially nutrition, remain to be explained. Possible explanations for the observed mortality differences will be explored. Breast cancer mortality rates have been correlated with other causes of mortality; both cancer and noncancer, using data obtained from 47 countries worldwide (World Health Organization). They have also been correlated with dietary data, especially concerning fat (animal and vegetal) intake (Food and Agricultural Organization). Highly significant correlations existed between breast cancer mortality and mortality from other cancers (e.g. colon, stomach) obtained from both sexes. These correlations have been confirmed over a period of more than 40 years. Highly significant positive correlations also existed with the intake of animal (saturated) fat, covering a period of 30 years. In multivariate regression, only the relationship with the colon, prostate cancer and total energy intake remained significant. Ecological data point to nutritional factors, especially animal fat, as major promoters of breast cancer mortality worldwide. This contrasts with the results of most cohort studies. These contradictory results and the relationship between breast cancer mortality and other causes of mortality remain to be explained. More refined and standardized dietary data are necessary.