ERBB2 and breast cancer: Despite the long history of data supporting deescalation of locoregional therapy in the field of breast cancer, uptake of deescalation practices has demonstrated significant geographic variation, starting with variable rates of breast conservation vs mastectomy documented in the 1980s.11 Little is known, however, about geographic variation in omission of RT and/or axillary surgery in women aged 70 years or older with HR+/ERBB2-negative (ERBB2−) breast cancer.