PGR and cardiac arrhythmia: The biological basis of these findings remains unknown, despite adjusting analyses for age, BMI, race, presence of brain metastasis and visceral disease, albumin, ECOG PS, ER/PR status, any prior taxanes, anthracycline or trastuzumab use, and the presence of hypertension, heart failure, coronary artery disease, cerebrovascular disease, arrhythmia, other CVDs or diabetes mellitus.