ESR1 and cancer: Undertreatment consisted of omission of radiation therapy in 154 of the 317 patients treated with breast conservation, omission of axillary node sampling in 61 of the 310 elderly patients with invasive cancers, omission of chemotherapy in 10 of 63 elderly patients with involved nodes, and omission of hormonal therapy in 59 of 321 elderly patients with estrogen receptor positive cancers.