Abnormal breast-tissue cellular antigen expression Increased breast-tissue progesterone receptor expression 2026-02-26T08:39:54Z Almost 70% of breast cancers are hormone receptor-positive. Their cells have positive expression of estrogen receptor (ER) and/or progesterone receptor (PR), which are related to cancer cell growth and spread. Estrogen and its receptor, ER, play a critical role in the development and progression of breast cancer. PR is an upregulated target gene of ER, its expression is dependent on estrogen, and PR can modulate ER action. PR is also a valuable prognostic biomarker of overall survival or disease-free survival in breast cancer.