Though there is not extensive research on this topic, one study  indicated that because women with dense breasts are at a greater risk of developing breast cancer, their risk of dying from breast cancer is about double that of the general population. Two other studies evaluated women with breast cancer and found an increased risk of death among women with fatty breasts; the reasons for this are not well understood [2, 3]. A recent analysis from The Netherlands showed a smaller estimated mortality reduction from screening mammography of 13% in women with dense breasts compared to 41% in women with fatty breasts. Reduced benefit from mammographic screening is attributed to the masking effect of dense tissue with tumors detected later, when they were larger, in women with dense breasts .
1. Chiu SY, Duffy S, Yen AM, Tabar L, Smith RA, Chen HH. Effect of baseline breast density on breast cancer incidence, stage, mortality, and screening parameters: 25-year follow-up of a Swedish mammographic screening. Cancer Epidemiol Biomarkers Prev 2010; 19:1219-1228
2. Gierach GL, Ichikawa L, Kerlikowske K, et al. Relationship between mammographic density and breast cancer death in the breast cancer surveillance consortium. J Natl Cancer Inst 2012; 104:1218-1227
3. Masarwah A, Auvinen P, Sudah M, et al. Very low mammographic breast density predicts poorer outcome in patients with invasive breast cancer. European radiology 2015; 25
4. van der Waal D, Ripping TM, Verbeek AL, Broeders MJ. Breast cancer screening effect across breast density strata: A case-control study. Int J Cancer 2017; 140:41-49