# Clinical Outcomes of Palbociclib and Letrozole in PALOMA-2

## Palbociclib plus letrozole clinical outcomes PALOMA-2

In PALOMA-2, palbociclib plus letrozole significantly improved progression-free survival by 13 months compared to letrozole alone (27.6 vs 14.5 months) with manageable hematologic toxicity and maintained quality of life, but did not demonstrate a significant overall survival benefit after 90 months of follow-up.

## Abstract

The PALOMA-2 trial demonstrated that palbociclib plus letrozole significantly improved progression-free survival compared to placebo plus letrozole in postmenopausal women with ER+/HER2- advanced breast cancer. Median PFS was 27.6 months versus 14.5 months (HR 0.56, P<0.0001), with consistent benefit observed across all patient subgroups including Asian patients (25.7 vs 13.9 months, HR 0.49, P=0.007) and those with low disease burden. Notably, PFS improvement occurred regardless of objective response status, with non-responders experiencing median PFS of 10.9 versus 5.6 months (HR 0.72, P=0.016). The treatment delayed time to subsequent chemotherapy by approximately 10 months (40.4 vs 29.9 months). However, after 90.1 months of follow-up, median overall survival was 53.9 versus 51.2 months (HR 0.96, P=0.34), showing no significant improvement.

The primary toxicity was hematologic, with grade 3-4 neutropenia occurring in 66.4% of patients (vs 1.4% with placebo), increasing to 89.2% in Asian populations. Despite this, febrile neutropenia remained rare (1.8-2.0%), and treatment discontinuation rates were low (9.7-12.2% vs 5.9%). Quality of life was maintained with no significant differences in FACT-Breast Total or EQ-5D scores between treatment arms, and pain scores significantly improved with palbociclib plus letrozole (P=0.0183). Neutropenia did not negatively impact quality of life measures.

## Methods

We analyzed 10 sources from an initial pool of 200, using 6 screening criteria. Each paper was reviewed for 8 key aspects that mattered most to the research question.

### Records from Elicit search

- n = 200  Papers screened using: PALOMA-2 Trial Relevance, Patient Population, Clinical Outcomes, Intervention Specificity, Disease Population Specificity, Study Design Appropriateness
- n = 200 Papers screened out
- n = 190 Papers included for extraction

## Data extraction

### Study Type

- Study phase: Phase 3 Randomized controlled trial
- Follow-up duration: Median follow-up time was 90.1 months

### Patient Population

- Total number of patients: 666 (444 to palbociclib plus letrozole, 222 to placebo plus letrozole)
- Key eligibility criteria: Postmenopausal women with ER+/HER2– advanced breast cancer, no previous systemic therapy for advanced disease

### Treatment Details

- Palbociclib dosing: 125 mg/day for 3 weeks on/1 week off
- Letrozole dosing: 2.5 mg/day continuously
- Median treatment duration was 22-30 months

### Efficacy Outcomes

- Progression-free survival: Median PFS was 27.6 months with palbociclib + letrozole versus 14.5 months with placebo + letrozole (HR 0.56, P<0.0001)
- Overall survival: Median OS was 53.9 months with palbociclib + letrozole versus 51.2 months with placebo + letrozole (HR 0.96, P=0.34)

### Safety Outcomes

- Most common adverse events: Neutropenia (81.8-82.2% in palbociclib + letrozole arm)

### Quality of Life

- Patient-reported outcomes were assessed using the FACT-Breast and EQ-5D questionnaires.
- The addition of palbociclib to letrozole maintained health-related QOL and improved pain scores

### Subgroup Analyses

All subgroups analyzed demonstrated benefit from the addition of palbociclib to letrozole.

### Clinical Implications

- Authors' interpretation: Palbociclib plus letrozole significantly improves PFS but not OS, with a consistent safety profile.

## Results

### Characteristics of Included Studies

The included publications comprised analyses from the PALOMA-2 trial, a phase 3 randomized controlled trial that enrolled 666 postmenopausal women with ER+/HER2- advanced breast cancer. Patients were randomized 2:1 to palbociclib plus letrozole (n=444) or placebo plus letrozole (n=222). Key eligibility criteria included no prior systemic therapy for advanced disease and performance status 0-2. Disease characteristics at baseline included measurable disease in 76-77% of patients, with approximately 48% having visceral disease and 52% non-visceral disease.

## Conclusion

The PALOMA-2 trial consistently demonstrated progression-free survival benefit with palbociclib plus letrozole across multiple follow-up analyses and patient subgroups, while overall survival did not reach statistical significance. This apparent discordance between PFS and OS outcomes merits further investigation.