Efficacy and toxicity of antibody-drug conjugates in older adults with breast cancer: A systematic review and meta-analysis

BACKGROUND: : Antibody-drug conjugates (ADCs) have reshaped breast cancer treatment, yet their efficacy and toxicity in older adults (≥65 years) remain poorly characterized. METHODS: : We searched PubMed, Ovid MEDLINE, and Embase (Elsevier) through November 17, 2025 for phase 2 or 3 randomized trials comparing ADCs versus non-ADC therapies in metastatic or early-stage breast cancer. The primary analysis assessed progression-free survival (PFS) in metastatic disease and invasive disease-free survival (IDFS) in early-stage disease, stratified by age (≥65 vs. <65 years), using pooled hazard ratios (pHRs). Age-by-treatment interaction was assessed using the ratio of HRs. Secondary outcomes included overall survival (OS) and grade ≥3 adverse events (AEs). RESULTS: Of 3,045 records identified, 20 trials (14 metastatic, 6 early-stage; 13,055 participants, 18% aged ≥65 years) met inclusion criteria. In metastatic trials, ADCs improved PFS in both older (pHR, 0.64; 95% CI, 0.51-0.79) and younger participants (pHR, 0.58; 95% CI, 0.51-0.66), with no significant age-by-treatment interaction (pooled ratio of HRs, 1.10; 95% CI, 0.91-1.33). ADCs also improved OS in the metastatic setting, though no trial reported age-stratified OS. In early-stage trials, only two reported age-stratified IDFS, with discordant results precluding pooled analysis. Grade ≥3 AEs were reported across all trials, but only three provided age-stratified data, and none stratified AEs jointly by treatment arm and age. CONCLUSION: ADC efficacy in metastatic breast cancer was similar across age groups, though data in early-stage disease were limited. Insufficient age- and treatment-stratified toxicity reporting precludes meaningful safety assessment of ADCs in older adults with breast cancer.