Is high breast density a risk factor for breast cancer ?

High breast density (HBD) tends to be seen as a significant and independent risk factor for breast cancer. This article describes a methodological and quantitative study of the variables selected by the large DMIST study, i.e., age, hormonal status and breast density, in correlation with cancer occurrence frequency. The statistical analysis of cancer rates in every patient subgroup of a study involving more than 42,000 women in screening, shows that HBD, when isolated from other variables, does not by itself constitute a significant risk factor, compared to the number of cancers detected in each density category. The DMIST study is unique and reliable, since it performs two different mammographic explorations of each patient, independently interpreted, thus minimizing the rate of false negatives. It appears then that the notion of density as a breast cancer risk factor is probably at least questionable. Admitting that HBD is an independent risk factor has a crucial economical health care impact, through the multiplication of different imaging modalities for women with HBD. Moreover, the physiological components of such a density are not well defined in each case, and grouping all types of breast composition under the unique label of density is haphazard. Breast tissue composition should be specifically studied in relation with cancer frequency, after isolating it from other impacting factors. Its evaluation needs thorough studies on vast populations, aiming at the analysis of a clearly isolated breast density variable on equal populations for each variable value, to perform a significant analysis of variance.