Do you rely on Ki67 as an estimate of proliferation to guide the decision for chemotherapy in premenopausal women with hormonally-driven breast tumors?  

Far from it. Especially in premenopausal women, Ki-67 is affected by circulating hormones and time of the month, and it is not a reliable indicator of endocrine resistance. In postmenopausal women, the most valuable Ki-67 reading is on endocrine therapy if any, not baseline either. Ki-67 should not ...