Yes. Dense breast tissue is a risk factor for the development of breast cancer: the denser the breast, the higher the risk . A meta-analysis across many studies concluded that magnitude of risk increases with each increase in density category, and women with extremely dense breasts (category D) have a 4-fold greater risk of developing breast cancer than do women with fatty breasts (category A), with upper limit of nearly 6-fold greater risk .
Most women do not have fatty breasts, however. More women have breasts with scattered fibroglandular density . In some populations, denser breasts are more common. For example, Asian women are often reported to have denser breasts than do other races; however, after accounting for age at mammography and BMI, the differences are modest [4-6]. Women with heterogeneously dense breasts (category C) have about a 1.5-fold greater risk of developing breast cancer than those with scattered fibroglandular density (category B), while women with extremely dense breasts (category D) have about a 2-fold greater risk.
There are probably several reasons that dense tissue increases breast cancer risk. One is that cancers arise microscopically in the glandular tissue. The more glandular tissue, the more susceptible tissue where cancer can develop. Glandular cells divide with hormonal stimulation throughout a woman’s lifetime, and each time a cell divides, “mistakes” can be made. An accumulation of mistakes can result in cancer. The more glandular the tissue, the greater the breast cancer risk. Women who have had breast reduction experience a reduced risk for breast cancer: thus, even a reduced absolute amount of glandular tissue reduces the risk for breast cancer. The second is that the local environment around the glands may produce certain growth hormones that stimulate cells to divide, and this is observed with fibrous breast tissue more than fatty breast tissue.
Risk for developing breast cancer is influenced by a combination of many different factors including age, family history of cancer (particularly breast and/or ovarian cancer), and prior atypical breast biopsies. Most women who develop breast cancer have no additional risk factors other than being female and aging.
Some risk factors can be influenced by behavior. Alcohol intake increases the risk of developing breast cancer, and the greater the intake, the greater the risk. Being overweight, especially after menopause, also increases the risk for breast cancer. Regular exercise reduces the risk of breast cancer.
There is currently no reliable way to fully know the interplay of breast density, family history, prior biopsy results, and other factors in determining overall risk. However, the largest study of its kind  found that dense breast tissue increases the risk of developing breast cancer more than family history, postmenopausal weight gain, or late childbearing.
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1. American Cancer Society. Breast Cancer Facts & Figures 2019-2020. Atlanta: American Cancer Society, Inc. 2019. Retrieved from https://www.cancer.org/content/dam/cancer-org/research/cancer-facts-and-statistics/breast-cancer-facts-and-figures/breast-cancer-facts-and-figures-2019-2020.pdf. Accessed April 20, 2020.
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