Validation of the DNA Damage Immune Response (DDIR) Signature in Triple-Negative Breast Cancer (TNBC) Patients from the SWOG 9313c Trial. Validation of the DNA Damage Immune Response (DDIR) Signature in Triple-Negative Breast Cancer (TNBC) Patients from the SWOG 9313c Trial

Purpose: The purpose of this study was to independently validate two biomarkers, a 44-gene DNA Damage Immune Response (DDIR) signature and stromal tumor-infiltrating lymphocytes (sTILs), as prognostic markers in TNBC patients treated with adjuvant doxorubicin (A) and cyclophosphamide (C) in SWOG 9313. Materials & Methods: 425 centrally determined TNBC cases from S9313 were identified. DDIR signature was performed on RNA isolated from FFPE tumor tissue (n=381), and samples were classified as DDIR-negative or positive using predefined cutoffs. Evaluation of sTILs was performed as previously described. Markers were tested for prognostic value for disease-free and overall survival (DFS, OS) using Cox regression models adjusted for treatment assignment nodal status and tumor size. Results: Among 425 TNBC patients, median age was 45 years, and 33% were node-positive. DDIR was successfully tested in 90% (381/425) of cases, of which 62% were DDIR signature-positive. DDIR signature positivity was associated with improved DFS (HR=0.67; 95% CI 0.48–0.92, P=0.014) and OS (HR=0.61; 95% CI 0.43–0.89, P=0.009). sTILs density assessment was available in 99% of patients and was associated with improved DFS (HR=0.70; 95% CI 0.51–0.96, P=0.028 for sTILs density ≥20% vs. <20%) and OS (HR=0.59; 95% CI 0.41–0.85, P=0.004 for sTILs density ≥20% vs. <20%). The DDIR signature score and sTILs density were moderately correlated (r=0.62) which precluded statistical significance for DFS in a joint model (P=0.08 for DDIR and P=0.25 for sTILs). Conclusion: The prognostic role of sTILs and DDIR in early-stage TNBC was confirmed. DDIR signature conferred improved prognosis in two-thirds of TNBC patients treated with adjuvant AC. DDIR signature has potential to stratify outcome and identify patients with less projected benefit following AC chemotherapy. Clinical trial number: Int0137 (The trial pre-dates Clinicaltrial.Gov website establishment) Overall design: For this validation cohort, 381 triple negative breast cancer patients were profiled on cDNA microarray, originally collected prospectively as part of the S9313 study. In S9313, patients with either high-risk node-negative or node-positive breast cancer were randomly assigned to one of two equivalent dose schedules of AC chemotherapy, given either sequentially or concurrently. A total of 13 process controls (ES-2 cell lines) were also included throughout microarray profiling for quality control and surveillance.