Biomarker-Based Update on Neoadjuvant Letrozole With or Without Ribociclib
Posted: Friday, July 10, 2020
Letrozole plus ribociclib is generally considered superior to letrozole alone in treating estrogen receptor–positive, HER2-negative, metastatic breast cancer. However, Qamar J. Khan, MD, of the University of Kansas Medical Center in Westwood, and colleagues conducted the biomarker-based FELINE trial to see whether differences in Ki67 protein levels and in reaching a preoperative endocrine prognostic index (PEPI) of 0 would be observed among 120 postmenopausal women receiving neoadjuvant treatment of letrozole plus placebo versus letrozole plus ribociclib. The Ki67 index is an on-therapy predictor of adjuvant recurrence, and the PEPI index is a predictor of a low risk of relapse without chemotherapy in estrogen receptor–positive breast cancer.
The team presented their study findings during the ASCO20 Virtual Scientific Program (Abstract 505). Adding ribociclib to letrozole as neoadjuvant therapy did not, in fact, produce a greater chance of reaching a PEPI score of 0. In addition to that primary endpoint, others completed cell-cycle arrest and any differences in response and toxicity between women who received ribociclib intermittently or continuously.
“At day 14, cycle 1, twice as many women treated with letrozole plus ribociclib had complete cell-cycle arrest compared with those who received letrozole plus placebo (92% vs. 52%),” noted Dr. Khan and co-investigators. However, more women who received ribociclib had “increased proliferation between day 14, cycle 1, and surgery, resulting in similar complete cell-cycle arrest at surgery” (71.4% vs. 63.3%), although the P value was not significant. In addition, they reported similar efficacy and toxicity in patients who received continuous and intermittent (3 weeks on, 1 week off) doses of ribociclib.
A total of 38 women were randomly assigned to receive letrozole plus placebo; 41 were given letrozole plus ribociclib intermittently; and 41 were administered letrozole plus ribociclib continuously for six 28-day cycles. Grade 3 or more adverse events were observed in 4 patients on the placebo arm, 23 patients on the intermittent-ribociclib arm, and 19 patients on the continuous-ribociclib arm.
Disclosure: The study authors’ disclosure information can be found at coi.asco.org.
