Cisplatin benefit is predicted by immunohistochemical analysis of DNA repair proteins in squamous cell carcinoma but not adenocarcinoma: theranostic modeling by NSCLC constituent histological subclasses

Most non-small-cell lung cancer (NSCLC) patients receive cisplatin-based chemotherapy though clinical response is restricted to a subset of patients. DNA repair protein levels are possible surrogates for cisplatin-induced DNA adduct (and subsequent cell death) repair efficiency and thus molecular determinants of therapeutic efficacy. The International Adjuvant Lung Trial (IALT)-Bio study previously suggested ERCC1 and MSH2 as predictive of cisplatin-based therapeutic benefit. DNA repair protein expression (XPF, BRCA1, ERCC1, MSH2, p53, PARP1, and ATM) was assessed by immunohistochemistry on a large subset of patients (N = 769) from the IALT trial. Tissue Microarray slides were digitally scanned and signal quantified by user-defined macros. Statistical analyses (univariate and multivariate) of 5-year disease-free survival (DFS) and 5-year overall survival used binary cut-offs (H score low/high expression). In patients with squamous cell carcinoma (SCC), ATM, p53, PARP1, ERCC1, and MSH2 displayed significant (borderline) predictive values, mainly on DFS with chemotherapy efficacy limited to low marker levels. Adenocarcinoma (ADC) results were not significant. BRCA1 and XPF were not significant for predictive modeling in either SCC or ADCs. Here predictive utility of DNA repair enzymes co-segregates with SCC histology, focusing their predictive value to this histological subclass of NSCLC. Distinct mechanisms of chemotherapeutic response or resistance might exist among histological subclasses of solid tumors.