ESR1 and breast cancer: In breast cancer subgroup analysis, high CT83 is considered as an unfavorable risk factor in PR-negative, node-positive, and Grade-1 subgroups for RFS, in ER-negative, HER2 subtype, node-positive, Grade-2, and Grade-3 subgroups for OS, and in HER2 subtype and node-negative subgroups for DMFS.