The triple-positive subgroup displays several peculiarities: (i) it had a significantly better prognosis than the group ER-PR-HER2+; (ii) TPBCs displayed a lower TP53 mutation rate than ER-PR-HER2+ breast cancers (30% vs 69%); and, (iii) TPBCs exhibited lower HER2 mRNA and protein expression than ER-PR+HER2+ tumors [82]. This evidence concerns the gene ESR1 and breast cancer.