The reported excess of left-sided breast cancer in older women is unlikely to be explained by differences in breast tissue composition.
Furthermore, the similarities between sides seen in middle-aged women suggest that any difference in the laterality of breast cancer in middle age and later is not likely to be explained by differences in breast density.
The change in PD in any given region therefore did not always equal the woman's mean overall PD change (Wald test, P < 0.01), but some of these within-woman regional differences in age-related changes in PD might be accounted for by differences in breast size (Table 1), compression and positioning between the two screens.
Women of higher socioeconomic status (SES) are at increased risk of developing breast cancer, but it is unclear to what extent this is mediated by differences in mammographic breast density, a well-established breast cancer risk factor.
"With further work, the increased cancer risk may not be confirmed; and even if it is, could turn out to be explained by differences in known breast cancer risk factors among shift workers vs non-shift workers.
As such, our understanding of tumour dormancy should be updated in light of current treatment methods (radiation, hormonal therapy and tumour targeted antibody treatments), which are likely influencing tumour dormancy in a different way now compared to patients in the era of Demicheli's database, as shown by vast differences in breast cancer mortality rates and recurrence patterns.
It is reported that diverse patterns of breast density by ethnicity are consistent with ethnic differences in breast cancer risk.
The only study of social inequalities by birth cohort found small educational differences in breast cancer mortality among women born after 1935 (Martikainen and Valkonen, 2000).
Our group has previously identified novel cancer stromal gene expression signatures associated with outcome differences in breast cancer by gene expression profiling of three soft tissue tumors, desmoid-type fibromatosis (DTF), solitary fibrous tumor (SFT), and tenosynovial giant cell tumor (TGCT/CSF1), as surrogates for stromal expression patterns.
Consequently, likely changes in exposures to risk factors for breast cancer by younger generations may well alter ethnic differences in breast cancer incidence in the future.
Some studies [ 37, 53, 55, 58, 59, 62, 64, 65] attempted to test for differences in breast cancer risk by MMR genes; for example, Scott et al. [ 58] observed an increased risk of breast cancer for MLH1 mutation-carrying families but not in MSH2 families (see Additional file 1 for details).
