CHEK2 and breast cancer: Our observation regarding no differential efficacy of first-line endocrine therapy for MBC between CHEK2 1100delC and non-CHEK2 patients is in line with the results of our previous study regarding no differential effect of adjuvant endocrine therapy on distant disease-free and BCSS in CHEK2 and non-CHEK2 early BC patients (Kriege et al. 2014).