Palbociclib Plus Letrozole Treatment After Progression to Second Line Chemotherapy for Women With ER/PR-positive Ovarian Cancer

Letrozole (Femara®) is an oral non-steroidal aromatase inhibitor that is approved worldwide for the treatment of postmenopausal women with breast cancer. It is administered orally on a continuous 2.5 mg daily dosing regimen and has a good toxicity profile. Palbociclib (Ibrance®) is an active potent and highly selective reversible inhibitor of cyclin- dependent kinases 4 and 6 (CDK4/6). Palbociclib was approved by the United States Food and Drug Administration (U.S. FDA) and the European Medicines Agency (EMA) for the treatment of postmenopausal women with hormone receptor (HR)-positive, human epidermal growth factor receptor 2 (HER2)-negative advanced or metastatic breast cancer in combination with an aromatase inhibitor based on a randomized, double-blind, placebo-controlled, international clinical trial PALOMA-2. It is administered orally on a dose of 125 mg per day in 4-week cycles (3 weeks of treatment followed by 1 week off). This trial was based on preclinical studies that showed a synergistic effect between targeting the ER and cyclin-D-CDK4/6-Rb pathway. The principal toxicity was myelotoxicity but it was managed with appropriate supportive care and dose reductions13. Based on the results of phase 1 and 2 clinical trials of CDK4/6 inhibitors used as monotherapy to treat patients with recurrent ovarian cancer, we hypothesized that, as Palbociclibe is active in this population and many ovarian cancer show ER/PR expression, its combination with Letrozole can improve outcomes in ER/PR positive endometrioid or high-grade serous Ovarian Cancer who have disease progression on second-line chemotherapy, similar to what is seen in breast cancer studies.