ESR1 and Headache: When considering the burden of headaches in both M and TTH, we found that the frequency of headache attacks was positively correlated with female HR expression in BC malignancies, although less for estrogen (ER) (r = 0.11, p = 0.05) than progesterone (PgR) (r = 0.15, p = 0.007) (Figure 1).