PGR and breast cancer: The use of biomarkers, such as estrogen receptor, progesterone receptor, and HER-2, for predicting breast cancer outcome or targeting endocrine therapy is widespread.[3] The diagnosis and treatment of breast cancer has progressed over the past few decades, however, recurrence and metastasis is still incurable and has become the biggest challenge in clinical treatment.[4] Therefore, finding new biomarkers and discovering their mechanisms in breast cancer is crucial for the diagnosis, treatment, and prognosis of patients with breast cancer.