The recently published ASTER 70s trial, the first phase 3 randomized trial dedicated to women aged ≥70 years with breast cancer, showed that in ER-positive, HER2-negative disease with high genomic risk by the Genomic Grade Index, the addition of adjuvant chemotherapy to hormonotherapy did not confer a statistically significant survival benefit but was associated with substantially greater toxicity34. This evidence concerns the gene ESR1 and breast cancer.