Women with dense breasts have at least four times the risk of breast cancer compared to those with less dense breasts (less dense breasts have a higher percentage of fat). Using hormone replacement therapy (HRT) appears to amplify the heightened risk associated with dense breasts. Both breast MRIs and ultrasounds can improve the detection of breast cancer in women with dense breasts. Perhaps surprisingly, breast density can be modified by diet, giving women an opportunity to influence this breast cancer risk factor.
Having dense breasts increases risk of breast cancer
Having dense breasts increases the risk of both main histological types of invasive breast cancer, ductal and lobular. Dense breasts are associated with hormone receptor positive (ER+/PR+) and mixed hormone receptor (ER+/PR- and ER-/PR+) breast cancer. Studies have reported conflicting results for hormone receptor negative (ER-/PR-) tumors. One 2012 study reported that percent mammographic density appears to be inversely associated with ER expression but might correlate positively with PR expression.
Women with dense breasts have a higher rate of second primary breast cancer (a new tumor that arises after treatment and that does not appear to be directly related to the first breast cancer).
Women with a decrease in breast density over time have been shown to have decreased breast cancer risk compared to women whose breast density remains stable.
Dense breasts can start early in life
Dense breasts run in families. High birth weight and childhood height, known risk factors for breast cancer, are associated with dense breasts. Also, older mothers (over 39 years of age) are more likely to have daughters with dense breasts.
Mammographic density has been found to be higher for women with first-degree relatives with breast cancer.
Environmental and dietary factory influence breast density and its effects
Breast density is not fixed; it can be increased or reduced by environmental exposures and food. One study found that a high protein diet, especially animal protein, was linked to higher breast density whereas higher vitamin D intake appeared to reduce it. Another study found that a high calorie diet in middle age was associated with increased breast density 15 years later. However, another study found that only high fat intake, especially saturated fat such as found in butter or beef, was associated with higher breast density.
Exposure to cadmium can increase breast density. Dietary sources of cadmium include shellfish, rice, flaxseed, escargot, sunflower seeds, and dried apricots from certain geographic regions. Alcohol consumption is also associated with increased breast density, and the association is stronger in women with a family history of breast cancer.
A high dietary omega-6 to omega-3 fatty acid ratio has been shown to reduce breast density in rats. Consuming foods high in carotenoids (e.g., carrots, pumpkins, saffron) has been shown to reduce the risk of breast cancer among women with high breast density.
Hormone replacement therapy, particularly combined estrogen plus progestin HRT, heightens the risk of breast cancer associated with dense breasts among postmenopausal women.
Breast cancer treatment reduces breast density
Aromatase inhibitor treatment reduces breast density. Chemotherapy reduces breast density, especially among younger women. Radiation treatment significantly reduces the risk of local recurrence among breast cancer patients with dense breasts who are treated with lumpectomy. One study found that 40% of women with high breast density who did not receive radiation therapy experienced local breast cancer recurrence by the 10-year mark.