TOP1 gene copy number in stage III colorectal cancer (CRC) samples: Association to prognosis.

Abstract

475 Background: TOP1 inhibitor treatment is frequently being used in combination therapy of metastatic CRC. This study aims to reveal whether TOP1 gene copy number associates with patient prognosis, since such a relationship may have significant implications for future studies aiming at validating the predictive value of TOP1 gene copy number. Methods: The study included TOP1 and CEN-20 FISH analyses (DAKO A/S Denmark) on FFPE tissue sections from 154 stage III CRC patients who did not receive adjuvant chemotherapy. TOP1 gene copy number, CEN-20 copy number and the TOP1/CEN-20 ratios were analyzed and correlated to overall survival (OS), to time to recurrence (TTR) of patients with CRC and to local recurrence (LR) in patients with rectal cancer (RC). Results: TOP1 copy number counts and the TOP1/CEN-20 ratios, age, gender and primary tumor location were separately added into a multivariate analysis as continuous variables. For OS and LR, TOP1 copy number was significant and the ratio was borderline significant with higher copy number associated with longer OS or longer time to LR. When the patients were dichotomized using the TOP1 median copy number, we found that patients with high TOP1 copy number in their tumor cells had a significant longer OS (HR: 0.68; 95% CI: 0.47-0.98; p = 0.04) compared to patients with low TOP1 copy number. Using the median TOP1/CEN-20 ratio to dichotomize, no significant differences were observed between patients with levels above or below the median ratio number for OS (HR: 0.76; 95% CI: 0.53-1.10; p = 0.14). TOP1 copy number divided the RC patients into two groups with a trend towards a significant difference in time to LR (HR: 0.56; 95% CI: 0.27-1.16; p = 0.11) with higher copy number. If the median ratio was used, a significant association with longer time to LR (HR: 0.43; 95% CI: 0.20-0.92; p = 0.03) was found. No significant associations between TOP1 copy number or ratio and TTR were observed. Conclusions: Increased TOP1 copy number is associated with longer OS in CRC patients and fewer LR in RC patients. Thus, future studies analyzing the association between TOP1 copy number and response to therapy in CRC patients should be planned in such a way that a prognostic and a predictive value of TOP1 can be separated.