In the context of combination therapy of tamoxifen and rIFN-β in MPNs, it is important to note that the potential of rIFN-α or rIFN-β to increase estrogen receptor expression in human breast cancer cells [186,187,188,189] and the possibility of improving tamoxifen’s efficacy through the addition of rIFN-α or rIFN-β have been addressed in several experimental and clinical studies of breast cancer over the last 25–30 years [186,187,188,189,190,191,192]. This evidence concerns the gene ESR1 and breast carcinoma.