This secondary (prospective-retrospective) analysis of the phase III IDEAL trial evaluated whether CanAssist Breast (CAB), a biomarker-based risk tool, could predict late distant recurrence and identify HR+/HER2- early breast cancer patients who benefit from 5 vs. 2.5 years of extended adjuvant letrozole, using a pooled cohort (n=3,052) and an IDEAL subset (n=627) followed for up to 15 years.
CAB stratified IDEAL patients into low-risk (60%), high-risk (28%), and ultra-high-risk (UHR, 12%) groups; the UHR subgroup had the greatest benefit from 5-year vs. 2.5-year extended endocrine therapy (ΔDRFS +10%), compared to minimal benefit in low-risk (ΔDRFS +1%) and high-risk (ΔDRFS +1.5%) groups.
Secondary retrospective analysis of a subset (627/IDEAL patients) limits causal inference; the IDEAL cohort was 73% node-positive vs. 43% in the pooled cohort, reducing generalizability to lower-risk populations; no multivariable or statistical significance testing results are reported in the abstract for the DRFS differences.
CAB's ultra-high-risk category (>20% recurrence risk) may identify the minority of HR+/HER2- patients most likely to benefit from a full 5 years of extended adjuvant letrozole — consider this tool when counseling patients about EET duration. Low- and high-risk CAB patients showed minimal DRFS benefit from longer EET and may be spared the added toxicity.
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