ESR1 and obesity due to melanocortin 4 receptor deficiency: When considered in the context of hormone-dependent tumors, our findings suggest a bidirectional action of Mφ in obesity-associated breast tumorigenesis, through which TAMs augment estrogen signaling in BC via upregulation of ERα (present study), while adipose tissue Mφ contribute to this augmentation through an increase in estrogen levels (via induction of aromatase expression in stromal cells of ‘obese’ adipose tissue [16,30,41,42]).