Functional mutations in PIK3CA (odds ratio (OR)=0.58; 95% confidence interval (CI)=0.49–0.69), GATA3 (OR=0.77, CI=0.6–0.99), MAP3K1 (OR=0.52, CI=0.4–0.68), KMT2C (OR=0.69, CI=0.52–0.94) and CBFB (OR=0.56, CI=0.38–0.83) were associated with lower grade in ER+ tumours. The gene discussed is CBFB; the disease is neoplasm.