Abstract 5235: Circulating tumor DNA as a prognostic marker in colorectal cancer: Preliminary results of a prospective trial
Authors: Laurent-Puig Pierre , Bouché Olivier , Niarra Ralph , Aucouturier Pascaline , Benhaim Leonor , Landi Bruno , Berger Anne , Lecomte Thierry , Normand Corinne , Le Corre Delphine , Didelot Audrey , Mallet Karine , Perez Toralla Karla , Hor Thevy , El Harrak Zakaria , Chatellier Gilles , Hutchison Brian , Link Darren , Taly Valerie 
Published: August 2015

Abstract
Circulating tumor DNA has been suggested to be a prognostic factor in different types of tumors. In order to investigate this role, we prospectively enrolled 250 patients with stage II and stage III colorectal cancer (NCT01198743). Plasma samples were collected before surgery (D0) and 5 days later (D5), then every 4 months during the 3 years of follow-up. The end of follow-up will be May 2017. The primary tumors were characterized for KRAS, NRAS, BRAF, PIK3CA, APC and TP53 mutation by sequencing. The circulating DNA was assessed by picoliter digital droplet PCR (dPCR) using the Raindrop instrument (Raindance technologies) with Taqman probes for the 7 most frequent mutations of KRAS and for the BRAF V600E mutation. The survival without recurrence curves were estimated with the Kaplan- Meier method. Differences between groups of patients were analyzed using unstratified log-rank tests. For comparisons of baseline characteristics, categorical outcomes were analyzed with χ2 tests and continuous outcomes were compared with standard parametric or nonparametric tests. Continuous variables are presented as the mean (SD) and median interquartile rang. We present here the results of tumor circulating DNA for the first 56 patients with KRAS or a BRAF mutated tumors. The mean age was 65.3±11 years [37-84], the gender ratio M/F was 0.9. The tumor location was proximal or distal in 55% and 45% respectively. TNM classification showed 49% and 51% of stage II and stage III respectively. The tumors were found mutated for BRAF in 9 cases (16%) and mutated for KRAS in 47 cases (84%). Finally 54% of the patients received an adjuvant chemotherapy. Tumor circulating DNA was found in 12 patients out of the 56 tested patients (23%). A mutation identical to that found in the tumor was identified at D0 or D5 after surgery before any chemotherapy treatment in the plasma of 12 patients (21.4%). For the patients with circulating tumor DNA, the mutated allele frequency in the plasma range from 0.2‰ to 1.4% (median 2.4‰). The detection of circulating tumor DNA was more frequent in patients with recurrence or death from the disease during the follow-up than those without at the time of diagnosis (45.4% versus 15.6%, p = 0.03). Patients without circulating tumor DNA before or 5 days after surgery have a significant better survival without recurrence than those with circulating tumor DNA detectable in univariate analysis (HR: 7.3 CI95% [1.7-31.5] p = 0.006). After adjustment on tumor stage this result remains significant (HR: 6.9 CI95% [1.5-32.9] p = 0.01) During the follow-up DNA was detected in 36.7% of patients who recurred or died from the disease as compared to 2.2% of those who do not (P = 0.004). These preliminary results showed a strong prognostic impact of circulating tumor DNA at the time of surgery and need to be confirmed in the whole series of 250 patients and with the complete follow-up of 5 years.
Citation Format: Pierre Laurent-Puig, Olivier Bouché, Ralph Niarra, Pascaline Aucouturier, Leonor Benhaim, Bruno Landi, Anne Berger, Thierry Lecomte, Corinne Normand, Delphine Le Corre, Audrey Didelot, Karine Mallet, Karla Perez Toralla, Thevy Hor, Zakaria El Harrak, Gilles Chatellier, Brian Hutchison, Darren Link, Valerie Taly. Circulating tumor DNA as a prognostic marker in colorectal cancer: Preliminary results of a prospective trial. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 5235. doi:10.1158/1538-7445.AM2015-5235