Abstract 642: Comparison between in situ hybridization and digital polymerase chain reaction methods for detecting c-MYC gene copy number gain in tissue and cell-free plasma samples of colorectal cancer patients

Abstract

Abstract Introduction: We focused on the utility of the droplet digital polymerase chain reaction (ddPCR) for detecting c-MYC gene copy number (GCN) gain in cell-free plasma and tumor tissue of CRC patients. Methods: c-MYC GCN was determined by using dual-color silver in situ hybridization (SISH) and ddPCR in retrospective cohort of 193 CRC patients (cohort 1) and prospective cohort of 64 CRC patients (cohort 2). Additionally, c-MYC GCN was analyzed by ddPCR method in cell-free plasma samples of cohort 2. Results: In cohort 1, c-MYC GCN gain, defined as mean c-MYC copies/nucleus ≥ 4.0 in SISH analysis, was observed in 34 (17.5%), and c-MYC GCN gain by ddPCR method in 7 (3.6%). c-MYC GCN by SISH was significantly correlated with ddPCR results (ρ= 0.532, P < 0.001). Forty cases (20.7%) showed intratumoral genetic heterogeneity, but it did not affect the concordance between SISH and ddPCR results (P > 0.05). c-MYC GCN gain by both SISH and ddPCR methods had the worst prognosis (P = 0.001). In cohort 2, c-MYC GCN by SISH was significantly associated with tissue ddPCR (ρ=0.349, P = 0.005), but not with plasma ddPCR (P = 0.620). Intratumoral genetic and regional heterogeneity of c-MYC status have been found in 29 (45.3%) and 8 (12.7%). c-MYC status in plasma was associated with tissue ddPCR, but borderline statistical significance (ρ= 0.246, P = 0.050). Conclusions: Our findings suggested that results by SISH and ddPCR methods were discordant. Therefore, detecting method should be carefully selected to determine c-MYC GCN status. Citation Format: Soo Hyun Seo, Kyu Sang Lee, Soo Kyung Nam, Kyoung Un Park, Heung-Kwon Oh, Duck-Woo Kim, Sung-Bum Kang, Hye Seung Lee. Comparison between in situ hybridization and digital polymerase chain reaction methods for detecting c-MYC gene copy number gain in tissue and cell-free plasma samples of colorectal cancer patients [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 642.