ESR1 and breast cancer: Interestingly, for PALB2, the risk of CBC was increased if the primary breast cancer was ER-negative (HR 2.9; 95% CI 1.4–6.4; p = 0.006), whereas it was increased for CHEK2 if the primary breast cancer was ER-positive (HR 2.0; 95% CI 1.1–3.5; p = 0.02) [47].