Women who smoke cigarettes have an increased risk of getting breast cancer if they carry a hobbled version of a key protective gene, researchers reported Tuesday.
The work, which contradicts previous studies finding no link between smoking and breast cancer, suggests that at least some of the puzzling rise in breast cancer in the past few decades may be due to increased smoking among women.
The critical gene, called NAT2, helps neutralize toxins and cancer-causing chemicals, including some present in cigarette smoke.
About half of white women, and a smaller percentage of blacks and Asians, inherit a relatively weak version of the gene. For them, smoking a pack or more of cigarettes a day quadruples the risk of getting breast cancer, according to a report in today’s Journal of the American Medical Association.
By contrast, women with a potent version of the detoxifying gene had no increase in breast cancer no matter how much they smoked - although their odds of getting other smoking-related ailments apparently remain high.
“It was very puzzling that tobacco was not looking like a risk factor for breast cancer in women. So we wondered, ‘Are there some who are susceptible and some who are not?”’ said Peter G. Shields of the National Cancer Institute.
That is exactly the case for postmenopausal women, according to the study of 631 women. NAT2 and smoking had no effect on breast cancer risk for premenopausal women, but researchers warned a link may appear later.
Breast cancer incidence has been increasing for the past two decades in the United States. Some of the rise is due to improved diagnosis, and there are theories that some may be due to factors such as increased fat in the diet and changes in childbearing patterns. But no one has been able to account for all of the increase.
NAT2 tests, which are performed on blood or urine specimens, are not widely available but sometimes can be obtained at a doctor’s request.