Progression-free Survival Outcome Is Independent of Objective Response in Patients With Estrogen Receptor-positive, Human Epidermal Growth Factor Receptor 2-negative Advanced Breast Cancer Treated With Palbociclib Plus Letrozole Compared With Letrozole: Analysis From PALOMA-2

Clin Breast Cancer. 2020 Apr;20(2):e173-e180. doi: 10.1016/j.clbc.2019.08.009. Epub 2019 Sep 5.

Abstract

Background: In PALOMA-2, palbociclib + letrozole significantly prolonged progression-free survival (PFS) versus placebo + letrozole in patients with estrogen receptor-positive/human epidermal growth factor receptor 2-negative (ER+/HER2-) advanced breast cancer (ABC). We investigated clinical outcomes of patients who achieved or did not achieve a confirmed objective response (OR) according to Response Evaluation Criteria in Solid Tumors (RECIST) version 1.1 (data cutoff: May 31, 2017).

Patients and methods: Postmenopausal patients untreated for ER+/HER2- ABC were randomized 2:1 to palbociclib + letrozole or placebo + letrozole. Median PFS, median duration of OR, baseline characteristics, and palbociclib exposure were compared in patients with or without OR by treatment arm.

Results: In the intent-to-treat population, OR was achieved by 194 (44%) of 444 and 77 (35%) of 222 patients in the palbociclib and placebo arms, respectively (odds ratio, 1.5; 95% confidence interval [CI], 1.0-2.1; P = .0156). Regardless of treatment, more OR than non-OR patients had de novo metastatic disease (47%-50% and 28%-31%, respectively) and no prior endocrine therapy (55% and 35%-37%, respectively). Rates of palbociclib dose reduction owing to adverse events were similar regardless of OR (41% and 38%, respectively). Among the patients with OR during the study, approximately 50% achieved OR within the first 3 months regardless of treatment. The median PFS was significantly prolonged with palbociclib + letrozole versus placebo + letrozole in patients with measurable disease in both OR (37.2 months; 95% CI, 28.1 months to not estimable vs. 27.4 months; 95% CI, 22.2-31.1 months; hazard ratio, 0.66; 95% CI, 0.47-0.94; P = .009) and non-OR groups (10.9 months; 95% CI, 8.2-11.2 months vs. 5.6 months; 95% CI, 5.3-8.3 months; hazard ratio, 0.72; 95% CI, 0.54-0.97; P = .016).

Conclusions: Palbociclib + letrozole provided significant clinical benefit versus placebo + letrozole to patients with ER+/HER2- ABC regardless of achieving RECIST-defined OR. Pfizer; ClinicalTrials.gov: NCT01740427.

Keywords: Cyclin-dependent kinase; Inhibitor; Metastatic breast cancer; Tumor response.

Publication types

  • Clinical Trial, Phase III
  • Multicenter Study
  • Randomized Controlled Trial

MeSH terms

  • Adult
  • Aged
  • Aged, 80 and over
  • Antineoplastic Combined Chemotherapy Protocols / therapeutic use*
  • Aromatase Inhibitors / therapeutic use
  • Breast / pathology
  • Breast / surgery
  • Breast Neoplasms / mortality
  • Breast Neoplasms / pathology
  • Breast Neoplasms / therapy*
  • Chemotherapy, Adjuvant
  • Female
  • Humans
  • Intention to Treat Analysis
  • Letrozole / therapeutic use*
  • Mastectomy
  • Middle Aged
  • Piperazines / therapeutic use*
  • Progression-Free Survival
  • Protein Kinase Inhibitors / therapeutic use
  • Pyridines / therapeutic use*
  • Receptor, ErbB-2 / metabolism
  • Receptors, Estrogen / metabolism
  • Response Evaluation Criteria in Solid Tumors*

Substances

  • Aromatase Inhibitors
  • Piperazines
  • Protein Kinase Inhibitors
  • Pyridines
  • Receptors, Estrogen
  • Letrozole
  • ERBB2 protein, human
  • Receptor, ErbB-2
  • palbociclib

Associated data

  • ClinicalTrials.gov/NCT01740427