STRAP Is a Strong Predictive Marker of Adjuvant Chemotherapy Benefit in Colorectal Cancer

BACKGROUND: Molecular predictors for the effectiveness of adjuvant chemotherapy in colorectal cancer are of considerable clinical interest. To this aim, we analyzed the serine threonine receptor-associated protein (STRAP), an inhibitor of TGF-βsignaling, with regard to prognosis and prediction of adjuvant 5-FU chemotherapy benefit. i The gene copy status of STRAP was determined using quantitative realtime polymerase chain reaction in 166 colorectal tumor biopsies, which had been collected from a randomized multicenter trial of 5-fluorouracil (5-FU)/mitomycin C (MMC) adjuvant chemotherapy of the Swiss Group for Clinical Cancer Research (SAKK). RESULTS: Amplification of STRAP was found in 22.8% of the tumors. When left without adjuvant chemotherapy, patients bearing tumors with a STRAP amplification had a significantly better prognosis (hazard ratio for death: 0.26; P = .004). Interestingly, these patients, when receiving adjuvant treatment, had a worse survival (hazard ratio for death: 3.48; P = .019) than without chemotherapy, whereas patients carrying tumors with diploidy or deletion of STRAP benefited from the treatment (hazard ratio for death: 0.44; P = .052). This suggests the amplification of STRAP as a strong predictor of an unfavorable effect of 5-FU-based adjuvant chemotherapy. CONCLUSION: If confirmed, the STRAP gene copy status might provide a parameter to decide about the use of 5-FU-based adjuvant chemotherapy.