ESR1 and breast cancer: In 2009, Heikkinen et al. reported that breast cancer patients harboring the PALB2 c.1592delT mutation were more likely to present the triple-negative phenotype (54.5%, p < 0.0001), characterized by the absent expression of estrogen receptor, progesterone receptor, and human epidermal growth factor receptor 2 (79), than other familial (12.2%) or sporadic (9.4%) breast cancer patients (80).