About 2/3 of breast cancer cells contain some amount of estrogen receptor expression, known as ER (+), which is known as ER-positive breast cancer, and 40% to 50% of breast cancers contain progesterone receptor expression, known as PR (+), which is known as PR-positive breast cancer. ER-positive and/or PR-positive breast cancers are sensitive to hormone therapy, and ER (+) or PR (+) Invasive breast cancer can be treated with endocrine therapy.