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) 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.