ESR1 and breast cancer: In a step-up logistic model, pathologic variables significantly predictive of a lower likelihood of having an ER+ breast cancer were high mitotic activity (RR 0.06, P < 0.001), geographic necrosis or fibrotic focus (RR 0.22, P = 0.02), and pushing/unknown margins (RR 0.24, P = 0.03).