Abstract 5233: Prediction and response evaluation of EGFR blockade for colorectal cancer by using circulating cell-free DNA

Abstract

Abstract Aim: In 10% of metastatic colorectal cancer patients, discordance of KRAS mutational status between primary tumor and metastatic tumor is observed. However biopsy of liver or lung metastasis is invasive and risky. Liquid biopsy (LB) is a new method of molecular diagnosis using circulating tumor DNA in peripheral blood. Here, we evaluated KRAS mutations using LB as a biomarker to predict the efficacy of EGFR blockade and observed concentration variability of ccfDNA by chemotherapy. Methods: We enrolled 44 colorectal cancer patients (14 KRAS mutant and 30 KRAS wild in primary tumors) with distant metastases. Circulating cell-free DNA (ccfDNA) was purified from 1 mL serum using the QIAamp Circulating Nucleic Acid Kit. We quantitated the concentration of ccfDNA and detected nine KRAS (G12A, G12R, G12D, G12C, G12S, G12V, G13D, Q61H, and Q61R) mutations. We administered EGFR blockade to 13 patients with KRAS wild in their primary tumor as the first line chemotherapy, and used computed tomography 3 months after starting EGFR blockade therapy to evaluate its effect. The study protocol was approved by the Ethics Review Committee of our institution. Written informed consent was obtained from each patient. Results: KRAS mutations in ccfDNA were detected in 85% (12/14) of patients with KRAS mutation in their primary tumor but in 10% (3/30) of patients without KRAS mutations in their primary tumors. In one of the 3 patients, primary tumor had wild KRAS but metastatic liver tumor and ccfDNA was mutated KRAS. We administered EGFR blockade to 13 patients. Twelve patients with KRAS wild in ccfDNA had a good clinical response (1CR and 12PR). One patient with KRAS mutation (G13D) in ccfDNA had no response. In majority of metastatic colorectal cancer patients, concentration of ccfDNA is more than 1000ng/ml. After curative resection, concentration of ccfDNA is less than 100ng/ml in non-metastatic colorectal cancer patients. In chemotherapy effective cases, the concentration of ccfDNA decreased immediately after administration, but the concentration of ccfDNA did not decrease in non-effective case. In our CR case, ccfDNA did not disappear (minimum 180ng/ml) while CR was continuing and new metastatic liver tumor appeared 28 weeks after detection of ccfDNA marked increasing. Conclusions: LB detection of KRAS mutations is less-invasive and repeatable compared with current techniques and may be useful for prediction of EGFR blockade. The concentration of ccfDNA decreased immediately in objective response case that is administered EGFR blockade. Conversely, the concentration of ccfDNA increased before imaging detection of disease progression. Citation Format: Takuma Iwai, Takeshi Yamada, Hatato Kan, Michihiro Koizumi, Seiichi Shinji, Goro Takahashi, Atushi Watanabe, Satoshi Matumoto, Akihisa Matuda, Aya Yamagishi, Yasuyuki Yokoyama, Eiji Uchida. Prediction and response evaluation of EGFR blockade for colorectal cancer by using circulating cell-free DNA. [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 5233. doi:10.1158/1538-7445.AM2015-5233