ESR1 and breast cancer: The LUMINA trial, for example, studied omission of radiation in patients ages 55 years and older with T1N0 breast cancer and luminal A subtype (defined on trial as: ER 1% or more, PR higher than 20%, ERBB2 negative, with Ki67 of 13.25% or lower), who were treated with adjuvant endocrine therapy alone after lumpectomy.