left-handedness seems to be associated with the risk of breast cancer

[Lani]

and an hypothesis of why that may be:

Br J Cancer. 2007 Aug 7; [Epub ahead of print]
Left-handedness and risk of breast cancer.

Fritschi L, Divitini M, Talbot-Smith A, Knuiman M.
1Western Australian Institute for Medical Research, Nedlands, Perth, Western Australia 6009, Australia.
Left-handedness may be an indicator of intrauterine exposure to oestrogens, which may increase the risk of breast cancer. Women (n=1786) from a 1981 health survey in Busselton were followed up using death and cancer registries. Left-handers had higher risk of breast cancer than right-handers and the effect was greater for post-menopausal breast cancer (hazard ratio=2.59, 95% confidence interval 1.11-6.03).British Journal of Cancer advance online publication, 7 August 2007; doi:10.1038/sj.bjc.6603920 www.bjcancer.com.
PMID: 17687338 [PubMed - as supplied by publisher]