The genomic grade index (GGI) does not predict a survival benefit with the addition of chemotherapy to adjuvant endocrine therapy in older patients with breast cancer, according to a presentation at the 2022 ASCO Annual Meeting.

In the intent-to-treat (ITT) population of a phase 3 trial, patients age 70 years or older who had estrogen receptor (ER)-positive, HER2-negative breast cancer and a high tumor GGI did not experience a significant improvement in overall survival (OS) when chemotherapy was added to endocrine therapy.

However, there was a significant OS improvement with chemotherapy among patients treated per protocol.


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The phase 3 ASTER 70s trial (ClinicalTrials.gov Identifier: NCT01564056) enrolled 1969 patients, 70 years and older, with ER+ HER2- primary breast cancer or isolated local relapse who had undergone curative surgery. 

There were 1089 patients with a high GGI who were randomly assigned to receive chemotherapy plus endocrine therapy (n=541) or endocrine therapy alone (n=548). Patients with a low GGI were followed in an observational cohort.

At a median follow-up of 5.94 years, there was no significant difference in OS between the chemotherapy and control arms in the ITT population. The 4-year OS was 90.6% in the chemotherapy arm and 89.4% in the control arm (hazard ratio [HR], 0.79; 95% CI, 0.60-1.03; P =.08). 

However, among patients treated per protocol, chemotherapy did provide an OS benefit. The 4-year OS rate was 91.0% in the chemotherapy arm and 89.3% in the control arm (HR, 0.73; 95% CI, 0.55-0.98; P =.03).

Results were similar for invasive disease-free survival (iDFS). In the ITT group, the 4-year iDFS rate was 86.2% in the chemotherapy arm and 82.5% in the control arm (HR, 0.79; 95% CI, 0.62-1.01; P =.06). 

In the per-protocol group, the 4-year iDFS rate was 86.8% in the chemotherapy arm and 82.4% in the control arm (HR, 0.74; 95% CI, 0.57-0.96; P =.03). 

Based on these results, the researchers concluded that GGI is prognostic but does not predict survival benefits with the addition of chemotherapy to endocrine therapy.

Disclosures: Some study authors declared affiliations with biotech, pharmaceutical, and/or device companies. Please see the original reference for a full list of disclosures. 

Reference

Brain E, Viansone AA, Bourbouloux E, et al. Final results from a phase III randomized clinical trial of adjuvant endocrine therapy ± chemotherapy in women ≥ 70 years old with ER+ HER2- breast cancer and a high genomic grade index: The UNICANCER ASTER 70s trial. Presented at ASCO 2022; June 3-7, 2022. Abstract 500.