Patients with MBBC tended to be older, more often infiltrating ductal carcinoma, the worse differentiated grade and had a higher proportion of ER and PR negative status both in the first tumor (11.11% vs 25.76%, 19.51% vs 34.52%, P < .001) and the second tumor (8.40% vs 24.72%, 18.03% vs 42.77%, P < .001). The gene discussed is ESR1; the disease is neoplasm.