Real-world utility of Histotype Px colorectal as a prognostic and potentially predictive biomarker.

215 Background: The decision to offer adjuvant chemotherapy (ACT) for patients with high-risk stage II and stage III colon cancer is fraught with challenges as most patients do not benefit from potentially toxic therapy. Histotype Px Colorectal stratifies patients into distinct risk groups by combining staging parameters with the DoMore v1 marker, a novel artificial intelligence-based digital biomarker that analyzes routine H&E-stained FFPE whole-slide images. The purpose of this study was to externally validate its prognostic performance and investigate its potential to predict adjuvant chemotherapy (ACT) benefit. Methods: This was a retrospective analysis of patients diagnosed with pathological stage II/III colon adenocarcinoma treated at Ohio State University in 2011-2024. Clinical parameters and outcome data were extracted from patient records. Blinded to clinical outcomes, anonymized digitized slides were analyzed by Histotype Px. Logrank test and Cox proportional hazards regression were used to analyze cancer-specific death (CSD). The multivariable models included age, sex, pN stage, pT stage, number of lymph nodes sampled, tumor perforation, lymphovascular invasion, perineural invasion, MSI status, and receipt of ACT. Competing risk analysis was used to calculate CSD rates. Results: Baseline characteristics of the 503 eligible patients included median age of 63 years (22-97), 54% male, 55% stage III, 61% right-sided tumors and 23% MSI, with 51% of patients receiving ACT and a median follow-up of 44 months. The DoMore v1 marker was statistically significant in both univariable (p<0.0001) and multivariable analysis with the clinicopathological markers (p=0.0010). Among the 298 patients in the Histotype Px low-risk group, 41.3% received ACT and their 5-year CSD rate was 6.1% (2.2%-12.8%) compared to 5.9% (2.7%-10.9%) for those that did not receive ACT. For the 123 Histotype Px intermediate-risk patients, 58.5% received ACT with a 5-year CSD rate of 17.5% (8.3%-29.5%) compared to 15.7% (6.2%-29.2%) without ACT. For the 81 Histotype Px high-risk patients, 76.5% received ACT with a 5-year CSD rate of 42.3% (21.9%-61.5%) compared to 58.3% (30.8%-78.1%) without ACT. In multivariable analyses, ACT benefit was observed in the high-risk group (HR 0.17, 95% CI 0.06-0.47; p=0.0007) but neither in the intermediate-risk (p=0.84) nor low-risk (p=0.16) group. Conclusions: Histotype Px Colorectal was able to improve risk stratification and showed promise as a predictive biomarker for ACT benefit in patients with stage II/III colon adenocarcinoma. Current standard-of-care ACT might not be sufficient for Histotype Px high-risk patients, while ACT might not be beneficial for Histotype Px low-risk patients.