PENELOPE-B

Background

Phase III, double-blind, placebo-controlled RCT. 1250 patients with HR+ HER2- early breast cancer with residual disease after neoadjuvant chemotherapy and high clinical-pathological risk (CPS+EG score ≥3, or ≥2 with ypN+). Rationale: residual disease after NACT identifies a high-risk subpopulation.

Interventions and follow up

Arm A: Palbociclib 125mg days 1–21 of 28-day cycle × 13 cycles (1 year) + standard endocrine therapy
Arm B: Placebo × 13 cycles + standard endocrine therapy
Primary endpoint: Invasive disease-free survival (IDFS)
mFollow up: 42.8 month

Results

IDFS: HR 0.93, 95% CI 0.74–1.17, P=.525 — not significant
4-yr IDFS: 72.3% vs 69.0%

Adverse events

Hematologic: grade ≥3 neutropenia 56.8% vs 0.9%; no increase in febrile neutropenia
Other: dose reduction 36.3%; discontinuation for AEs 5.7% vs 1.4%

Conclusions

Palbociclib added to endocrine therapy did not improve IDFS in HR+ HER2- early BC patients with residual disease after NACT. The trial was negative, providing no basis for CDK4/6 inhibitor use in the post-NACT residual disease setting.

Key Limitations

Key Limitations: CPS+EG score enriched for high-risk patients but remains a non-validated composite endpoint with limited cross-trial use. Duration of palbociclib was only 1 year (vs 2 years in monarchE) — insufficient exposure may have limited efficacy. Absolute IDFS difference was numerically small but imprecision in HR confidence interval is wide. No molecular biomarker stratification (Ki-67, PIK3CA, ctDNA).

Clinical Context

PENELOPE-B represents the second negative palbociclib adjuvant trial. Unlike abemaciclib (monarchE positive), palbociclib has failed in both unselected early BC (PALLAS) and residual-disease post-NACT settings. Not approved for early BC. The residual-disease approach was validated for capecitabine (CREATE-X) and trastuzumab emtansine (KATHERINE) in other subtypes — but not for CDK4/6 inhibition in HR+ BC.

References

References: Loibl S et al, JCO 2021