Not all breast tumors are the same. Pathologists perform tests on breast tumors to learn what helps them grow. Your oncologist uses the information from these tests to make treatment recommendations. All breast tumors are tested to see if they have estrogen receptors (ER) and/or progesterone receptors (PR). Those that do are called hormone receptor (HR) positive. These tumors are likely to respond to the breast cancer drugs referred to as estrogen blockers or anti-estrogen treatments.
You can learn more about hormone-sensitive tumors here.