In summary, we describe the genetic dissection of the gene desert breast cancer susceptibility locus Mcs1a. We hypothesize that the resistance allele (from the Cop strain) carrying a truncated, potential transcriptionally suppressive COUP-TF (autoregulatory) binding motif, leads to increased Nr2f1 transcript levels in the mammary gland, which increases luminal RMEC differentiation and creates a less proliferative, more differentiated mammary epithelium with decreased mammary carcinoma susceptibility (Figure 8). Here, TF is linked to breast carcinoma.