Being left-handed could double breast cancer risk

Left-handed women are more than twice as likely as right-handers to suffer from breast cancer before reaching menopause, Dutch scientists said on Monday. More than a million women are diagnosed with breast cancer worldwide each year. Three quarters of cases occur after menopause, which usually begins around the age of 50. Some studies have shown that lesbians are at a higher risk of breast cancer than heterosexual women of the same age.

Researchers at the University Medical Center in Utrecht in the Netherlands speculate that there is a shared origin early in life for both left-handedness and developing breast cancer, possibly exposure to hormones in the womb. "Left-handedness is associated with breast cancer, most specifically premenopausal breast cancer," said Cuno Uiterwaal, an assistant professor of clinical epidemiology at the university, in an interview.

He and his colleagues studied 12,000 healthy middle-aged women born between 1932 and 1941 who were part of a breast-screening program. The scientists determined the hand preference of each woman and followed up on her medical history to see which women developed breast cancer.

"If we take premenopausal and postmenopausal breast cancer, then there was a 40% increased risk," Uiterwaal said of left-handed women who participated in the study. Upon further study, however, the scientists found most of the excess risk was in breast cancer before menopause. "We found that left-handed women are more than twice as likely to develop premenopausal breast cancer as non-left-handed women," the researchers said in the report published online by the British Medical Journal.

Other risk factors such as family history of breast cancer, numbers of pregnancies, smoking habits, and social and economic status were considered.

About 8% to 9% of all women are left-handed. But the scientists said the findings should not alarm them. "What our study intends to do is focus on this area. We do not know all the causes of breast cancer; that is why we should continue. This may be one new factor that leads us to a better understanding of the etiology," Uiterwaal added.

About 5% to 10% of breast cancers are hereditary. Most are due to mutations in the BRCA1 or BRCA2 genes. The earlier the illness is diagnosed and treated, the better the prognosis is for the woman.

"Although the underlying mechanisms remain elusive, our results support the hypothesis that left-handedness is related to increased risk of breast cancer," the researchers added. (Reuters, with additional reporting by Advocate.com)