Breast Cancer Race Differences Have Link to Vitamin D Gene
Specifically, a variant dubbed rs2239186 in the gene for the vitamin D receptor, which is associated with higher serum levels of 25OHD, decreased the risk of breast cancer in African Americans, with an odds ratio of 0.53 (95% CI from 0.31 to 0.79) which was significant at P=0.03. The gene variant had no effect in those of European ancestry.
After correcting for multiple testing, two variants in the CYP24A1 gene - rs27622941 and rs2209314 - had differential associations by race. The variant rs27622941 was associated with more than a doubling of the risk of ER-negative cancer in African Americans (OE 2.62, 95% CI 1.38 to 4.98), but had no effect in women of European ancestry.
On the other hand, rs2209314 was associated with a lower risk among those of European ancestry (OR 0.38, 95% CI 0.20 to 0.73), but had no association with risk among African Americans.
Yao and colleagues found that the increased risk of ER-negative cancer in African Americans became non-significant after adjustment for the two variants in CYP24A1.
"It is difficult to determine the exact effect of low levels of vitamin D on the risk of developing breast cancer," Yao said in a statement.
Black women prone to deadlier breast cancer
Younger black women who get breast cancer are far more likely than other afflicted women to have a particularly aggressive and lethal form of the disease, a study found.
The findings suggest that biology may help explain why breast cancer is deadlier in black women younger than 55 than it is in white women in the same age group. Other studies have blamed inadequate screening rates.
Since 1990, the average annual breast cancer death rate for younger black women in the United States has been 15.4 deaths per 100,000 population, versus 9.3 per 100,000 for younger white women.
“It’s been long known that breast cancer in African-American women is a far less common disease than in white women. But when it occurs, it seems to be more aggressive and harder to treat,” said study co-author Dr. Lisa Carey of the University of North Carolina’s Lineberger Comprehensive Cancer Center.
In the study in Wednesday’s Journal of the American Medical Association, researchers identified cancer types by looking for certain proteins in tumor tissue taken from 496 women in the Carolina Breast Cancer Study. The women had been diagnosed between 1993 and 1996.
A quick-spreading form of breast cancer called the basal-like subtype appeared in 39 percent of premenopausal black breast cancer patients. It accounted for 14 percent of breast cancer cases in older black women, and 16 percent of those in non-black women of any age.
But, Yao added, “our results show that these genetic variations, which contribute to the function of vitamin D, are strongly associated with ER-negative breast cancer and may contribute to the more aggressive breast cancer features seen in African-American women.”
African-American women are more likely than all other women to die from breast cancer. Their tumors often are found at a later, more advanced stage. So, there are fewer treatment options. Some other reasons for this may include not being able to get health care or not following-up after getting abnormal test results. Other reasons may include distrust of the health care system, the belief that mammograms are not needed, or not having insurance. Also, research has shown that African-American women are more likely to get a form of breast cancer that spreads more quickly.
We do not know how to prevent breast cancer. But there are things you can do to reduce your risk, such as limiting how much alcohol you drink and being physically active.
There also are things you can do to find breast cancer early. Breast cancer screening looks for signs of cancer before a woman has symptoms. Screening can help find breast cancer early when it’s most treatable. Two tests are commonly used to screen for breast cancer:
- Mammograms. A safe, low-dose x-ray exam of the breasts to look for changes that are not normal. Starting at age 40, women should have screening mammograms every 1-2 years. Depending on factors such as family history and your general health, your doctor may recommend a mammogram before age 40.
- Clinical breast exam (CBE). The doctor looks at and feels the breasts and under the arms for lumps or anything else that seems unusual. Ask your doctor if you need a CBE.
The researchers cautioned that they did not have enough patients and controls to create a validation cohort for the findings. As well, they added, the analysis only included three genes in the vitamin D pathway.
The study was supported by the U.S. Army Medical Research and Material Command, the National Cancer Institute, the Breast Cancer Research Foundation, and a gift from the Philip L Hubbell family.
The journal said the authors declared no competing interests.
Primary source: Breast Cancer Research
Source reference: Yao S, et al “Variants in the vitamin D pathway, serum levels of vitamin D, and estrogen receptor negative breast cancer among African-American women: a case-control study” Breast Cancer Research 2012; 14: R58; DOI: 10.1186/bcr3162.
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