The PALLAS trial investigated the addition of palbociclib to standard adjuvant endocrine
therapy to reduce breast cancer recurrence. This pre-specified analysis was conducted
to determine whether adjuvant palbociclib benefited patients diagnosed with lower
risk stage IIA disease compared to those with higher stage disease.PALLAS was an international,
multicenter, randomized, open-label, phase III trial, representing a public-private
partnership between Pfizer, the Austrian Breast Cancer Study Group, and the U.S. ALLIANCE
Foundation. Patients diagnosed with stage II-III, hormone-receptor-positive, HER2/neu
negative breast cancer within 12 months of diagnosis had completed all definitive
therapy aside from endocrine therapy (started within 6 months prior to study entry)
were eligible. All patients were required to submit a formalin-fixed paraffin-embedded
(FFPE) tumor block. Patients were randomly assigned 1:1 to receive standard adjuvant
endocrine therapy (of physicians' choice) for at least 5 years with or without 2 years
of palbociclib, administered orally at a starting dose of 125 mg daily, given for
21 days followed by a 7-day break.A total of 5,796 patients with HR + /HER2- early
breast cancer (including 1,010 with stage IIA) were enrolled. Median follow-up was
50 months for stage IIA patients and 43.1 months overall. In the stage IIA cohort,
4-year iDFS in the palbociclib arm was 92.9% versus 92.1% for ET alone (HR 0.75, 95%CI
0.48-1.19, p = 0.23). There was no differential benefit by histologic grade, chemotherapy
receipt, age, or anatomic/clinical risk. Additionally, no benefit to palbociclib was
seen in this cohort in invasive breast cancer-free survival (iBCFS), locoregional
relapse-free survival (LRFS), distant relapse-free survival (DRFS), or overall survival
(OS). For the stage IIB/III patients, 4-year iDFS was 85.3% for palbociclib + ET versus
83.6% for ET alone (HR 0.91, 95% CI 0.77-1.07, p = 0.24).While there were substantial
differences in outcome for stage IIA versus IIB/III patients at 4 years of follow-up,
the addition of 2 years of palbociclib did not improve outcomes for patients, regardless
of stage.ClinicalTrials.gov number NCT02513394 Registered 30 Jul 2015.
