Validation of the 12-gene colon cancer recurrence score (RS) in NSABP C07 as a predictor of recurrence in stage II and III colon cancer patients treated with 5FU/LV (FU) and 5FU/LV+oxaliplatin (FU+Ox).

Abstract

3512 Background: Standardized clinical tools which accurately quantify recurrence risk are needed for optimal adjuvant treatment of colon cancer. The 12-gene RS has been validated in stage II colon cancer pts from QUASAR and CALGB 9581. We conducted a large prospectively-designed clinical validation study of RS, w/ pre-specified endpoints, methods, and analysis plan, in stage II and III colon cancer pts randomized to FU or FU+Ox in NSABP C-07. Methods: 50% of C-07 pts w/ tissue were randomly selected, stratified on stage (AJCC 6th) and recurrence. Gene expression was quantitated by RT-PCR on 25 µm manually microdissected fixed colon tumor tissue. Data were analyzed by Cox regression controlling for stage and treatment (TRT). Results: RT-PCR was successful in 892/921 pts (97%): 449 FU, 443 FU + Ox; 264 st II, 409 st IIIA/B, 219 st IIIC. The primary endpoint was met: RS predicted recurrence (HR/25 units=1.96, 95% CI 1.50-2.55 p<.001). RS also predicted disease-free survival (p<.001) and overall survival (p<.001). RS predicted recurrence (p=.001) independent of T and N stage, MMR, nodes examined, grade, and TRT. Predefined high RS group (26% of pts) had higher recurrence risk than low RS group (39% of pts): HR=2.11, p<.001. Cox model 5 yr recurrence risk (95%CI) in FU treated pts by RS group (low, int, high): st II 9% (6-13%), 13% (8-17%), 18% (12-25%); st IIIA/B 21% (16-26%), 29% (24-34%), 38% (30-46%); st IIIC 40% (32-48%), 51% (43-59%), 64% (55-74%). RS did not have significant interaction w/ stage (p=0.90) or age (p=0.76). Relative benefit of Ox was similar across range of RS (interaction p=0.48); accordingly, in Cox model and Kaplan-Meier analyses, absolute benefit of Ox increased w/ higher RS. Conclusions: RS predicts recurrence risk in stage II and III colon cancer, capturing underlying biology and providing risk information beyond conventional factors. RS is not predictive of relative benefit of Ox added to adjuvant FU but enables better discrimination of absolute Ox benefit as a function of risk. Incorporating RS into the clinical context may better inform adjuvant therapy decisions for pts w/ stage III as well as stage II colon cancer.