In a case-only analysis of invasive breast cancer modeling the odds of ER negative cancer, conditional on cancer having occurred, nonmenstrually-related migraine was positively associated with estrogen-receptor negative (ER−) cancer whereas menstrually-related migraine was negatively associated with estrogen-receptor negative (ER−) cancer (combined-analysis test of heterogeneity P = 0.06) (Table 3). Here, ESR1 is linked to cancer.