With respect to histology, compared to women with ER+/PR+ tumors, women with ER+/PR- tumors had elevated risks of mortality if their tumor was ductal or lobular, women with ER-/PR+ tumors had elevated risks of mortality if their tumor was ductal or inflammatory, and women with ER-/PR- tumors had elevated risks of mortality across all histologies, except for medullary carcinoma. This evidence concerns the gene ESR1 and medullary thyroid gland carcinoma.