Purpose: We recently presented evidence for tumor site and gender-specificity in the survival benefit from adjuvant chemotherapy in Stage III colorectal cancer (CRC). In the current study, we examined whether p53 alteration or the microsatellite instability (MSI) phenotype provide additional predictive information in CRC patients.
Experimental design: A retrospective series of 891 Stage III CRC patients with negative surgical margins was investigated. Thirty percent (270 of 891) received postoperative adjuvant chemotherapy with curative intent and comprising of 5-fluorouracil/levamisole. Adjuvant treatment and nontreatment patient groups were well matched for tumor site, grade, p53 alterations, and MSI. Surgical tumor specimens were investigated for p53 overexpression using immunohistochemistry and for p53 mutation and MSI using single-strand conformation polymorphism analysis. The predictive value of these markers was evaluated by comparing the survival of adjuvant-treated and nonadjuvant treated patients.
Results: A strong inverse correlation was observed between p53 alteration and MSI (P < 0.0001). In univariate analysis, the factors of sex, site, p53 alteration, and MSI were each strong predictors of a survival benefit from chemotherapy. Multivariate analysis revealed that chemotherapy provided maximal survival benefit for female patients (P = 0.005) and for patients whose tumors contained normal p53 (P = 0.041). Males whose tumors contained a p53 alteration and were negative for MSI appeared not to benefit from chemotherapy.
Conclusions: Our findings suggest that p53 alteration and MSI could be clinically useful molecular predictive markers for the identification of CRC patients who might benefit from 5-fluorouracil-based chemotherapy.