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Addition of Palbociclib to Letrozole in Estrogen Receptor–Positive Breast Cancer

By: Joseph Fanelli
Posted: Thursday, February 21, 2019

For patients with early estrogen receptor–positive early breast cancer, the addition of neoadjuvant palbociclib to letrozole enhanced the suppression of malignant cell proliferation (Ki67), according to findings from the phase II PALLET trial published in the Journal of Clinical Oncology. The combination therapy also increased the rates of cell-cycle arrest and reduced apoptosis, concluded Stephen Johnston, MD, PhD, of The Royal Marsden National Health Service Foundation Trust, London, and colleagues.

However, according to the study authors, “[The combination] did not increase the clinical response rate over 14 weeks, which was possibly related to a concurrent reduction in apoptosis.”

Enrolled in the study were 307 postmenopausal women with estrogen receptor–positive primary breast cancer and tumors of at least 2 cm. Patients were randomly assigned to receive letrozole at 2.5 mg/d for 14 weeks (n = 103); letrozole for 2 weeks, then palbociclib plus letrozole to 14 weeks (n = 68); palbociclib for 2 weeks, then palbociclib plus letrozole to 14 weeks (n = 69); or palbociclib plus letrozole for 14 weeks (n = 67).

Clinical response between the palbociclib plus letrozole and letrozole groups was not significantly different (progressive disease rate of 3.2% vs. 5.4%, respectively). The median log-fold change in Ki67 was –4.1 with palbociclib plus letrozole and –2.2 with letrozole, among the 190 evaluable patients. More patients treated with palbociclib plus letrozole achieved complete cell-cycle arrest (90%)                                                           

As for toxicity, grade 3 or greater adverse events occurred in more patients treated with palbociclib plus letrozole than in those traeted with letrozole alone (50% vs. 17%).  The main adverse event was asymptomatic neutropenia.

Disclosure: The study authors’ disclosure information may be found at ascopubs.org.



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