Addition of palbociclib to standard endocrine therapy does not improve outcome in adjuvant treatment

Although adjuvant therapy with CDK4/6-inhibitors has shown to benefit patients with advanced/metastatic hormone receptor (HR)-positive/HER2-negative breast cancer, the final analysis of the PALLAS trial showed no benefit of adjuvant palbociclib for patients with early HR-positive/HER2-negative breast cancer.

The use of CDK4/6 inhibitors combined with endocrine therapy is a standard of care for advanced HR-positive/HER2-negative breast cancer, supporting the rationale to study CDK4/6 inhibition in the early breast cancer setting. PALLAS (NCT02513394) is a randomised, phase 3, open-label trial in which patients with stage 2–3 HR-positive/HER2-negative early breast cancer were randomised to receive either 2 years of palbociclib with adjuvant endocrine therapy or endocrine therapy alone. A total of 5,761 patients (median age 52 years, range 22–90) were enrolled; 17.6% had stage 2A disease and 82.1% stage 2B/3. Of all randomised patients, 82.5% had received prior (neo)adjuvant chemotherapy. After a protocol-planned, second interim analysis in May 2020, the study crossed the futility threshold [1]. Now, Prof. Michael Gnant (Medical University of Vienna, Austria) presented the results of the final analysis of PALLAS [2].

After a median follow-up of 31 months, invasive disease-free survival (iDFS) was similar between the 2 arms, with 3-year iDFS of 89.3% for palbociclib plus endocrine therapy and 89.4% for endocrine therapy alone (HR 0.96; 95% CI 0.81–1.14). Subgroup analyses revealed no significant interactions between treatment effect and other factors (including risk category).

“With the full number of events, this analysis of the PALLAS trial shows that the addition of 2 years of palbociclib to ongoing adjuvant endocrine therapy does not improve survival endpoints for patients with stage 2–3 HR-positive/HER2-negative early breast cancer,” concluded Prof. Gnant.

1. Mayer EL, et al. Lancet Oncol. 2021; 22: 212-222.
2. Gnant M, et al. Adjuvant palbociclib in HR+/HER2- early breast cancer: Final results from 5,760 patients in the randomized phase III PALLAS trial. GS1-07, SABCS 2021 Virtual Meeting, 7–10 December.

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Posted on 31 January, 2022