These data are consistent with published work showing a high rate of luminal B diagnoses in young women.1,32 However, in our cohort, Ki67 did not correlate with parity status, suggesting that, although Ki67 likely assists with identifying patients with ER-positive cancer at greatest risk for metastasis, it does not appear to delineate postpartum patients at increased risk. The gene discussed is ESR1; the disease is cancer.