PRL and breast cancer: Reportedly, BC normalizes PRL levels in 80%‐90% of cases, and reduces tumour size in ~70% cases.3 As in previous studies, we herein define BC resistance as the failure to normalize PRL levels or to reduce tumour size by ≥50%, after taking ≥15 mg/day of BC for at least 3 months.4, 5 The mechanisms of BC resistance are unclear, although reduced expression of D2R is believed to be the main factor.3