ESR1 and neoplasm: Table 2 and eFigure 6 in Supplement 1 present the HRs for PFS between mILC and mIDC according to metastasis onset, ER expression level, and tumor grade. Multivariable analysis showed better prognosis in mILC than mIDC (HR, 0.92; 95% CI, 0.85-1.00; P = .049) (eTable 1 in Supplement 1).