American women of African ancestry are more likely than European Americans to have estrogen-receptor-negative (ER-negative) breast cancer

Research has shown that specific genetic variations in the vitamin D receptor (VDR) and in CYP24A1 (responsible for deactivating vitamin D) are associated with an increase in breast cancer risk — particularly for ER-negative breast cancer — for African-American women. When researchers compared levels of vitamin D in the blood of women without breast cancer, they found that severe vitamin D deficiency in African-American women was almost six times more common than in European-American women. The researchers found that African-American women with the highest levels of vitamin D also had a specific variation in VDR. Although this variation was present in European Americans, it was not associated with alteration in their levels of vitamin D. African-American women with the specific variation associated with the higher levels of vitamin D had half the risk of breast cancer compared to women without it. When the researchers looked in detail at the patterns of genetic variation for women with ER-negative breast cancer, they found that seven SNPs in the gene coding for CYP24A1 were associated with ER-negative breast cancer risk, and that two of these seemed to account for the higher risk of ER-negative breast cancer in African-American women.