An AI Model Identifies Chemotherapy Benefit in Node-Negative HR+/HER2- Breast Cancer Patients from TAILORx, a Phase 3 Randomized Clinical Trial

BACKGROUND The prescribing of adjuvant chemotherapy for patients with breast cancer must balance the survival benefit against treatment-related toxicities. TAILORx, a phase 3 randomized clinical trial, demonstrated that endocrine therapy alone was, on average, noninferior to chemoendocrine therapy for patients classified as intermediate risk by a 21-gene Recurrence Score (RS) assay. Uncertainty remains about the optimal strategy to identify which intermediate-RS individuals derive benefit from chemotherapy. METHODS We analyzed 6735 patients from the TAILORx trial using Ataraxis Breast CTX with pathology images (H&E slides) and RS available. CTX is an AI model which integrates morphologic features extracted from H&E-stained slides with clinical variables to generate individualized predictions of prognosis (CTX-prognostic) and chemotherapy benefit (CTX-benefit). No data from TAILORx were used to train CTX and CTX was not retrained or recalibrated for this study. Analyses were prespecified in a protocol approved by ECOG-ACRIN. RESULTS Among patients treated with endocrine therapy alone, CTX-prognostic predicted disease-free interval (DFI), with a hazard ratio per 1 SD increase of 1.651 (95% CI, 1.511-1.803, p < 0.001) and C-index of 0.736 (95% CI, 0.697-0.770). Performance was similar in patients treated with chemoendocrine therapy (hazard ratio = 1.642 [95% CI, 1.495-1.804, p < 0.001], C-index = 0.720 [95% CI, 0.681-0.756]). After adjusting for the RS, CTX-prognostic remained significantly associated with DFI in both treatment groups. In the intermediate-RS subgroup, the treatment-by-biomarker interaction for CTX-benefit was significant (p = 0.001), with patients identified as high-benefit deriving a 5% increase in observed 5-year DFI rates from the addition of chemotherapy, compared with no detectable benefit in low-benefit patients. Stratifying the same subgroup by RS at a threshold selecting a similar proportion of patients yielded no significant interaction (p = 0.20). CONCLUSIONS In an analysis of TAILORx, CTX-prognostic stratified patients according to their risk of recurrence. Among intermediate-RS patients, CTX-benefit identified who derived clinically meaningful benefit from adjuvant chemotherapy, a population currently not identifiable by the RS alone.