ERCC1 and thymidylate synthase mRNA levels predict survival for colorectal cancer patients receiving combination oxaliplatin and fluorouracil chemotherapy.

Abstract

To test the hypotheses of whether the relative mRNA expression of the thymidylate synthase (TS) gene and the excision cross-complementing (ERCC1) gene are associated with response to and survival of fluorouracil (5-FU)/oxaliplatin chemotherapy in metastatic colorectal cancer. Patients had progressive stage IV disease after unsuccessful 5-FU and irinotecan chemotherapy. All patients were evaluated for eligibility for a compassionate 5-FU/oxaliplatin protocol. cDNA was derived from paraffin-embedded tumor specimens to determine TS and ERCC1 mRNA expression relative to the internal reference gene beta-actin using fluorescence-based, real-time reverse transcriptase polymerase chain reaction. The median TS gene expression level from 50 metastasized tumors was 3.4 x 10(-3) (minimum expression, 0.18 x 10(-3);maximum expression, 11.5 x 10(-3)), and the median ERCC1 gene expression level was 2.53 x 10(-3) (minimum, 0.0; maximum, 14.61 x 10(-3)). The gene expression cutoff values for chemotherapy nonresponse were 7.5 x 10(-3) for TS and 4.9 x 10(-3) for ERCC1. The median survival time for patients with TS <or= 7.5 x 10(-3) (43 of 50 patients) was 10.2 months, compared with 1.5 months for patients with TS greater than 7.5 x 10(-3) (P < .001). Patients with ERCC1 expression <or= 4.9 x 10(-3) (40 of 50 patients) had a median survival time of 10.2 months, compared with 1.9 months for patients with ERCC1 expression greater than 4.9 x 10(-3) (P < .001). A TS of 7.5 x 10(-3) segregated significantly into response, stable disease, and progression (P = .02), whereas the association between ERCC1 and response did not reach statistical significance (P = .29). These data suggest that intratumoral ERCC1 mRNA and TS mRNA expression levels are independent predictive markers of survival for 5-FU and oxaliplatin combination chemotherapy in 5-FU-resistant metastatic colorectal cancer. Precise definition of the best TS cut point will require further analysis in a large, prospective study.