Migraine is a common headache disorder affecting approximately one in five women worldwide. Women are three times more likely to experience migraines compared to men, suggesting a potential role for circulating sex hormones (particularly estrogens) in migraine pathophysiology. Given that estrogens are also implicated in breast carcinogenesis, epidemiologic studies have explored the association between migraines and breast cancer risk. Although fewer than ten studies have been conducted, most report a protective association, where presence of a migraine disorder was associated with a lower risk of breast cancer. However, these findings are limited by their reliance on physician-diagnosed migraines, despite evidence that many women with migraines never receive a formal physician diagnosis. Further, the observed protective associations may be confounded by differences in healthcare utilization, which have not been adequately addressed in previous studies. Overall, this makes it difficult to fully understand migraines as either a protective or risk factor for breast cancer, limiting insights into underlying biological mechanisms, accurate risk assessments, and guidance for clinical practice. The overall aim of this project is to examine associations between migraine and breast cancer risk, specifically to: 1) Describe agreement between self-reported and physician-diagnosed migraine measures; 2) Examine associations between self-reported and physician-diagnosed migraines and breast cancer risk (without adjustment for healthcare utilization); 3) Evaluate the potential confounding effect of healthcare utilization on the relationship between migraines and breast cancer risk. The results aim to enhance our understanding of the relationship between migraines and breast cancer risk, laying the groundwork for future studies on biological mechanisms and risk assessment.
