HER2DX genomic assay in HER2-positive early breast cancer treated with trastuzumab and pertuzumab: A correlative analysis from a real-world cohort.
BACKGROUND: HER2DX genomic assay is a genomic tool developed for personalizing care in early-stage HER2-positive breast cancer. This real-world analysis examines its associations with pathological complete response (pCR) and invasive disease-free survival (IDFS) following trastuzumab- and pertuzumab-based neoadjuvant therapy. MATERIALS AND METHODS: Retrospective, observational, single-center study of 156 patients with stage I-III HER2-positive breast cancer treated with dual HER2 blockade-based neoadjuvant therapy between February 2015 and May 2022 at University Hospital A Coruña. HER2DX and clinicopathological variables were assessed in pretreatment tumor biopsies. Statistical analyses included Fisher's exact test, logistic regression, Cox proportional hazards models, and Kaplan-Meier estimates. RESULTS: HER2DX was performed in 111 tumors (71.2%). Overall pCR rate was 51.3%. Hormone receptor-positive disease was significantly associated with lower pCR (odds ratio [OR] 0.25, 95% CI 0.11-0.50; p < 0.001), whereas HER2 immunohistochemistry 3+ showed a non-significant trend toward higher pCR (OR 2.95, 95% CI 0.96-11.08; p = 0.075). Median IDFS was not reached, but hormone receptor-positive tumors showed better outcomes (hazard ratio [HR] 3.67, 95% CI 1.02-13.32; p = 0.004 by log-rank). The association between HER2DX pCR score and pCR appeared heterogeneous. The continuous score was significantly associated with pCR in univariable analysis, not in multivariable model. In contrast, medium-high HER2DX pCR category showed significantly higher pCR rates than low category (OR 4.83, 95% CI 1.72-14.65; p = 0.004). The continuous HER2DX risk score was independently associated with IDFS (HR 2.84, 95% CI 1.24-6.48; p = 0.010). CONCLUSIONS: In this cohort, HER2DX scores were associated with pCR and IDFS, supporting previous evidence and highlighting potential role in treatment stratification.