Hormone receptor positive or hormone positive breast cancer cells have either estrogen er or progesterone pr receptors or both these breast cancers can be treated with hormone therapy drugs that lower estrogen levels or block estrogen receptors. Updates on 2 studies monarche and penelope b evaluating the use of cdk4 6 inhibitors in treating people with hormone receptor positive her2 negative breast cancer who have a high risk of breast cancer recurrence after primary treatment. Hormonal therapy is only used for breast cancer that is hormone receptor positive this means that the cancer cells have receptors for estrogen er progesterone pr or both when cancer cells have these receptors the hormones can attach to them and help them grow. Subjects were 486 patients with primary breast cancer who underwent surgery and postoperative tamoxifen monotherapy in 1982 1993 using representative sections of the primary lesion in each patient estrogen receptors er were immunohistochemically stained