The following article features coverage from the 2020 San Antonio Breast Cancer Symposium. Click here to read more of Cancer Therapy Advisor‘s conference coverage.

Although the addition of 1 year of palbociclib to standard adjuvant endocrine therapy initially delayed invasive disease for patients with hormone receptor (HR)-positive, HER2-negative, primary breast cancer at a high risk of relapse, the benefit disappeared with longer follow-up.

The first analysis of the phase 3 PENELOPE-B trial ( Identifier: NCT01864746) were presented at the 2020 Virtual San Antonio Breast Cancer Symposium (SABCS).

The trial enrolled patients who had a less than pathologic complete response following neoadjuvant taxane-containing chemotherapy, and randomized 1250 patients to receive either standard-of-care adjuvant endocrine therapy plus placebo for 1 year or endocrine therapy plus palbociclib for 1 year.

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At a median follow-up of 43 months, no difference in invasive disease-free survival (IDFS) was seen between the palbociclib arm and endocrine therapy–alone arm (hazard ratio [HR], 0.93; 95% CI, 0.74-1.17; P =.525), a finding that was consistent among subgroups.

Although an absolute difference of 4.3% was seen at 2 years for IDFS between the palbociclib arm and endocrine-alone arm (88.3% vs 84%, respectively), the absolute difference dwindled to 0.6% by 4 years (73% vs 72.4%).

Similarly, no difference in overall survival was seen between endocrine therapy plus palbociclib and endocrine therapy alone (HR, 0.87; 95% CI, 0.61-1.22; P =.420).

Patients in the endocrine therapy plus palbociclib arm had significantly more grade 3/4 adverse events (80% vs 20%; P <.001), especially grade 3/4 hematological adverse events (73% vs 1%; P <.001) compared with patients in the endocrine therapy–alone arm.

Study presenter Sibylle Loibl, MD, PhD, of the German Breast Group, concluded that the results of the PENELOPE-B study do not support the addition of 1 year of palbociclib to endocrine therapy. “It could be that the treatment duration with one year is too short, but we don’t know that.”

However, Dr Loibl added, “Long-term follow-up from all adjuvant CDK4/6 inhibitor studies should continue and must be awaited.”

Read more of Cancer Therapy Advisor‘s coverage of the 2020 SABCS meeting by visiting the conference page.


Loibl S, Marmé F, Martin M, et al. Phase III study of palbociclib combined with endocrine therapy (ET) in patients with hormone-receptor-positive (HR+), HER2-negative primary breast cancer and with high relapse risk after neoadjuvant chemotherapy (NACT): First results from PENELOPE-B. Presented at: 2020 Virtual San Antonio Breast Cancer Symposium; December 8-11, 2020. Abstract GS1-02.