Abstract 1912: An explorative analysis of ERCC1/ERCC4 copy number alterations in a chemonaive stage III colorectal cancer patient cohort.
Authors: Smith David H. , Jensen Niels F. , Christensen Ib J. , Müller Sven , Nielsen Hans J. , Brünner Nils , Nielsen Kirsten V. 
Published: August 2014

Background: Platinum-based chemotherapy is widely used in the treatment of cancer. Oxaliplatin, used in combination with 5-Fluorouracil in colorectal cancer (CRC), induces DNA damage which leads to death of the cancer cell. Oxaliplatin DNA damage can be removed by the nucleotide excision repair system. Two components of this system, ERCC1 and ERCC4, have previously been implicated in sensitivity/resistance to platinum-based treatment. The present study explores the mechanism, frequency and prognostic impact of ERCC1 and ERCC4 gene alterations in advanced CRC.

Methods: Fluorescent In Situ Hybridization (FISH) probes directed at ERCC1 (location: 19q13.32) and ERCC4 (location: 16p13.12) were constructed. Nine CRC cell line metaphase spreads were analyzed with an ERCC1 probe in combination with a reference probe covering the centromeric region of chromosome 2 (CEN-2) and with an ERCC4 probe combined with CEN-16. FFPE tissue sections from 152 stage III CRC (81 colon, 71 rectum) chemonaive patients were analyzed. Relationships between biomarker status and overall survival (OS) and time to recurrence (TTR) were analyzed using multivariate statistics.

Results: ERCC1 alterations were observed in a single cell line metaphase (HT29), whereas no alterations were observed with ERCC4. Among the 152 patient tumor sections which were successfully analyzed with ERCC1/CEN-2, 43 (28.3%) patients harbored an ERCC1 aberration, specifically: 2 (1.3%) deletions (ERCC1/CEN-2 &lt; 0.8) and 41 (27.0%) gains (ERCC1/CEN-2 ≥ 1.5). ERCC1 gains were detected in 17 (21.0%) and 24 (33.8%) colon and rectum tumor specimens, respectively; whereas ERCC1 deletions were only detected in colonic tumors. Increased ERCC1 gene copy numbers, when analyzed as a continuous variable, were significantly associated with longer survival (HR: 0.32, 95% CI: 0.14-0.75, p=0.01) and TTR (HR: 0.34, 95% CI: 0.12-1.00, p=0.0498) in tumors of the colon, but not with rectal tumors (OS HR: 1.01, p=0.66; TTR HR: 0.87, p=0.77). Similarly, ERCC1 gains (ERCC1/CEN-2 ≥ 1.5) showed a trend towards longer OS (HR: 0.46, 95% CI: 0.20-1.02, p=0.06) and TTR (HR: 0.44, 95% CI: 0.17-1.14, p=0.09) for patients with tumors of colonic origin, but not for those with rectal tumors. The impact of ERCC1 deletions were not analyzed due to the low number of patients, and were excluded from survival analysis. No ERCC4 aberrations were detected and scoring was discontinued after 50 patients.

Conclusions: ERCC1 gene gain occurs frequently in stage III CRC, whereas ERCC1 loss occurs infrequently. Higher ERCC1 counts and ERCC1/CEN-2 ratios were significantly associated longer OS and TTR in patients with colonic tumors. Accordingly, ERCC1 gain (ERCC1/CEN-2 ≥ 1.5) showed a similar tendency towards longer OS and TTR for colonic tumors. Future studies will investigate the effect of ERCC1 aberrations in a platinum-treated CRC patient population.

Citation Format: David H. Smith, Niels F. Jensen, Ib J. Christensen, Sven Müller, Hans J. Nielsen, Nils Brünner, Kirsten V. Nielsen. An explorative analysis of ERCC1/ERCC4 copy number alterations in a chemonaive stage III colorectal cancer patient cohort. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 1912. doi:10.1158/1538-7445.AM2013-1912