Chemotherapy effectiveness in trial-underrepresented groups with early breast cancer: A retrospective cohort study

Area of Science:

• Oncology
• Biostatistics
• Public Health

Background:

• Adjuvant chemotherapy improves early-stage breast cancer survival but trial data excludes elderly and comorbid patients.
• Uncertainty exists regarding chemotherapy's effectiveness in these underrepresented groups, impacting clinical decisions.
• This study uses real-world data (RWD) to address this knowledge gap.

Purpose of the Study:

• To estimate the effectiveness of adjuvant chemotherapy in early breast cancer patients aged 70 years and over.
• To assess chemotherapy's effectiveness in early breast cancer patients with high comorbidity.
• To inform clinical decision-making for trial-underrepresented patient populations.

Main Methods:

• Utilized Scottish Cancer Registry (2001-2015) linked to routine health records.
• Employed propensity score matching (PSM) and instrumental variable (IV) analysis for causal inference.
• Defined high comorbidity using Charlson index, inpatient stays, and outpatient visits.

Main Results:

• For women aged ≥70, PSM estimated HR for death was 0.73 (95% CI 0.64-0.95), indicating reduced mortality.
• For women with high comorbidity, PSM estimated HR for death was 0.67 (95% CI 0.51-0.86).
• Estimated 10-year survival benefit of ~3% for ≥70 group and ~4% for high comorbidity group.

Conclusions:

• Adjuvant chemotherapy appears generalizable to elderly and comorbid early breast cancer patients.
• Real-world data suggests chemotherapy is effective in trial-underrepresented groups.
• Findings should be interpreted cautiously alongside randomized trial data.