Palbociclib use does not extend IDFS for high-risk breast cancer patients
medwireNews: The PENELOPE-B investigators have found no invasive disease-free survival (IDFS) benefit with a 1-year course of palbociclib alongside endocrine therapy for hormone receptor-positive breast cancer patients who did not achieve a complete pathologic response to neoadjuvant chemotherapy.
As reported at the 2020 San Antonio Breast Cancer Symposium, the phase 3 trial included HER2-negative breast cancer patients with a high risk of relapse based on a clinical pathological stage–estrogen/grade staging system (CPS–EG) score of 3, or of 2 plus at least one positive lymph node after neoadjuvant chemotherapy and surgery and/or radiotherapy.
Presenting the results, Sibylle Loibl (German Breast Group, Neu-Isenburg) said that after a median 42.8 months of follow-up, there was no significant difference in IDFS between the 631 patients who were randomly assigned to receive 13 cycles of palbociclib 125 mg/day for 21 days out of each 28-day cycle plus endocrine therapy and the 619 patients who instead received placebo with their endocrine therapy.
The 3-year IDFS rate was 82.1% with palbociclib and 77.7% with placebo, and further analysis did not identify any patient subgroups who benefited from the addition of the CDK4/6 inhibitor.
In addition, an interim overall survival analysis did not find any difference between the palbociclib and placebo treatment arms of the study, with 3-year rates of 93.6% and 90.5%, respectively.
Loibl said there were “no new safety signals observed” in the trial.
Hematologic adverse events (AEs) were significantly more common with palbociclib than placebo, both at any grade (99.2 vs 79.1%) and at grade 3 or worse (73.1 vs 1.3%), but nonhematologic AEs and serious AEs were comparable in the two treatment groups.
Nevertheless, the full course of therapy was completed by 80.5% of palbociclib-treated patients and 84.5% of controls, with dose reductions most common early in the study. The main reasons for discontinuation were the patient’s choice (8.9 and 6.6%, respectively) and adverse events (5.2 and 0.8%).
And although the palbociclib-treated patients had a lower relative total dose density than the controls, the presenter described this as being “still satisfactory,” at a median 82.1% versus 98.9%.
“This is the first study showing mature [I]DFS results on a CDK4/6 inhibitor as part of (postneo)adjuvant therapy,” Loibl concluded.
“To date the results of PENELOPE-B do not support the addition of 1 year palbociclib to endocrine therapy,” she said, but emphasized that long-term follow-up is awaited for adjuvant CDK4/6 inhibitor, as well as translational research and subgroup analyses.
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