Abstract 4514: A comparison of two methodologies to quantify Thymidylate synthase for predicting survival in patients with colorectal cancer treated on CALGB 89803

Abstract

Abstract Background: Thymidylate synthase (TS) levels determined by immunohistochemistry (IHC) have been shown to be associated with decreased survival in retrospective studies of patients with colorectal cancer (CRC). The ratio of nuclear to cytoplasmic TS determined by automated quantitative analysis (AQUA™) has been reported to significantly predict a decreased time to recurrence in these same patients. The purpose of this study was to determine whether TS measured by the AQUA™ method predicts response in the CALGB 89803 patient sample, and to determine if the AQUA™ measurement of TS is prognostic compared to the standard IHC method. Methods: Tissue samples from 629 participants were evaluated from an IRB-approved randomized trial of 5-FU/LV/CPT-11 in patients with stage III CRC. TS levels were evaluated by IHC in 463 samples, by AQUA™ in 416 samples, and by both methods in 250 samples. TS staining by IHC was categorized as 0; 1+; 2+; 3+. TS staining by AQUA™ localizing to the nucleus, cytoplasm, and the ratio of the two (nucleus/cytoplasm), were classified as continuous measurements standardized by the highest observed value. The impact of each measure on survival (OS) and disease-free survival (DFS) was investigated using the logrank test and the proportional hazards model. Statistical correlations between the two measures were estimated using polyserial correlation. Results: In TS levels measured by IHC, there were no significant differences in OS. There was a significant difference in DFS (logrank p=0.047), with increased DFS among patients with higher TS levels. The nuclear and ratio AQUA™ TS measurements did not predict OS, but cytoplasmic TS marginally predicted OS (Cox model p=0.07). There were significant associations between nuclear and cytoplasmic TS and DFS (Cox model p=0.019 and p=0.007, respectively) with higher TS levels associated with increased DFS. DFS was marginally associated with the ratio (Cox model p=0.069). Correlation between TS staining measured by IHC and AQUA was low, while the correlation between the nuclear and cytoplasmic AQUA measurements was high (0.90 Pearson estimate). In multivariable models, the continuous measures of nuclear and cytoplasmic TS were each superior to TS measured by IHC in predicting DFS (logrank p=0.03 and 0.1 respectively); the ratio was not. Conclusions: TS levels measured by IHC and AQUA™ in the nucleus and cytoplasm predicted increased DFS with higher levels contrary to previous reports presenting significantly decreased survival for patients with higher TS tumor levels. The continuous measures for TS in the nucleus and cytoplasm were highly correlated and more strongly associated with outcome than TS measured by IHC. Given these results, further studies of TS as a prognostic predictor, and the use of the AQUA™ method as an alternate measurement of TS expression in colorectal tumors are warranted. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 4514. doi:1538-7445.AM2012-4514