Higher frequency of left-breast cancer: a possible explanation

A study of 1027 women with unilateral breast cancer showed that ipsilateral breast cancer was more common before age 45 and contralateral thereafter. The data suggest a possible explanation of the higher incidence of left-breast cancer in American women. A higher percentage of left-handed women developed breast cancer before age 45, but the over-all incidence of unilateral breast cancer was not greater in left-handed women than in right-handed or ambihanded subjects.