Is There a Link Between Left-Handedness and Breast Cancer?
A meta-analysis weighed the evidence on being a lefty and breast cancer.
Posted March 4, 2026 | Reviewed by Lybi Ma
Left-handedness and sex hormones: Could there be a link to cancer risk?
Overall, 10.6 percent of people are left-handed, but we know that men are slightly more likely to be left-handed than women ( Papadatou-Pastou and co-workers, 2008 ). This finding suggests that sex hormones likely affect whether someone is left-handed. For example, estrogens, a class of female sex hormones, have been thought to potentially affect the probability of being left-handed ( Schachter, 1994 ). Interestingly, sex hormones have also been shown to affect the risk of breast cancer. This suggests that left-handed and right-handed women may show differences in breast cancer risk. However, existing studies on the question of whether left-handed women have a higher risk of developing breast cancer do show conflicting results—small sample sizes and differences in study methodology may have an influence.
A meta-analysis on left-handedness in women and breast cancer risk
What is the best piece of evidence we have regarding the question of whether or not left-handedness in women is linked to a higher breast cancer risk? It probably comes from a 2024 meta-analysis , published in the scientific journal Therapeutic Advances in Medical Oncology ( Oh and co-workers, 2024 ). The research team, led by scientist Chi Young Oh from Pusan National University in South Korea, reviewed published studies on left-handedness and breast cancer and conducted a meta-analysis of research data. A meta-analysis is a statistical integration of data from several studies, with the advantage of a larger sample size and therefore more trustworthy findings than single studies. Overall, eight studies were included in the meta-analysis, which is a fairly low number of studies (some meta-analyses include several hundred studies).
What did the scientists find out?
The scientists conducted two main analyses. A first analysis comparing case versus control studies comparing breast cancer patients and healthy controls did not find a significant effect. Thus, patients were not more likely to be left-handed than controls. A second analysis of cohort studies (studies that start with a large group of healthy people and observe who develops cancer) found a small statistically significant effect, showing that left-handed women were a little bit more likely to develop breast cancer than right-handed women. When premenopausal and postmenopausal women were analyzed separately, the effect reached significance for premenopausal women but not postmenopausal women. An additional analysis of genetic data from the studies did not show a significant link between left-handedness and breast cancer.
Take-Away: Links between breast cancer and left-handedness are small and unlikely to be clinically relevant
Altogether, the meta-analysis only showed weak evidence for a link between left-handedness and breast cancer. While there was a statistically significant effect for premenopausal women, the absence of effects for post-menopausal women, case-control studies, and genetic data suggest that left-handedness is not a major risk factor for breast cancer. Given that only eight studies were included in the meta-analysis, more research on left-handedness and breast cancer is needed to draw any definite conclusions.
Oh, C. Y., Kim, E., Kim, K., Oh, H., Yoon, J. P., Goh, T. S., Son, E., Ko, D. S., & Kim, Y. H. (2024). Exploring the handedness-breast cancer nexus: a comprehensive analysis via systematic review, meta-analysis, and Mendelian randomization. Therapeutic advances in medical oncology , 16 , 17588359241305096. https://doi.org/10.1177/17588359241305096
Papadatou-Pastou, M., Martin, M., Munafò, M. R., & Jones, G. V. (2008). Sex differences in left-handedness: a meta-analysis of 144 studies. Psychological bulletin , 134 (5), 677–699. https://doi.org/10.1037/a0012814
Schachter S. C. (1994). Handedness in women with intrauterine exposure to diethylstilbestrol. Neuropsychologia , 32 (5), 619–623. https://doi.org/10.1016/0028-3932(94)90149-x
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Sebastian Ocklenburg, Ph.D., is a professor for research methods in psychology at the Department of Psychology at MSH Medical School in Hamburg, Germany. His research focuses on left-handedness and brain asymmetries.
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