Are left-handed women at increased risk for breast cancer? A new study suggests that might be the case.

Cuno Uiterwaal of the University Medical Center in the Netherlands and colleagues examined the relationship between handedness and breast cancer in 12,178 healthy, middle-age women from Utrecht participating in a breast cancer screening study.

Between 1982 and 2000, the left-handed women in the study were more than twice as likely as right-handed women to develop breast cancer before going through menopause, the researchers found. The association held up even after the researchers took into account other factors, such as social and economic status, smoking habits, family history of breast cancer, and reproductive history.

Much more research is needed to explore whether the relationship is real and what may explain it. But the researchers speculated that left-handed women may be at risk for breast cancer because they were exposed to higher levels of certain hormones in the womb.

"The origin of the association may lie in intrauterine exposure to steroid hormones," they wrote in a paper published online yesterday by the British Medical Journal. Women exposed to the hormonal drug diethylstilbestrol, or DES, for example, when they were in the womb were more likely to be left-handed, they noted.

"Although the underlying mechanisms remain elusive, our results support the hypothesis that left-handedness is related to increased risk for breast cancer," they wrote.