Concordance of Acquired Mutations between Metastatic Lesions and Liquid Biopsy in Metastatic Colorectal Cancer Treated with Anti-EGFR Therapy

Abstract Background: Acquired mutations are detected in plasma. However, still few reports examine the concordance between liquid biopsy and metastatic lesions with acquired resistance. Herein we evaluated whether a polymerase chain reaction-reverse sequence-specific oligonucleotide (PCR-rSSO) method can examine the concordance between liquid biopsy and metastatic lesions with acquired resistance.Methods: Firstly, we examined the presence of acquired mutations in 7 chemoresistant metastatic lesions and blood samples obtained from a metastatic colorectal cancer (mCRC) patient without RAS activating mutations treated with anti-EGFR treatment. The patient (patient 1) displayed initial early tumor shrinkage and finally progressed to disease (PD). Blood samples were collected before the development of PD and after acquiring resistance. Next, we evaluated RAS and BRAF mutational status among blood samples, primary tumors, and metastatic lesions obtained from three additional mCRC patients without RAS activating mutations. Acquired mutations were examined using Sanger sequencing and the PCR-rSSO approach.Results: Of patient 1, metastatic tumor specimens harbored diverse acquired mutations in the KRAS gene in all of the 7 (100%) metastases, and the three acquired mutations were detected in blood specimens collected after acquiring resistance. Next, we analyzed primary tumors, metastatic lesions after chemotherapy, and blood samples from three additional mCRC patients but noted that none of the patients exhibited mutations in liquid biopsy except for one case with BRAF V600E mutation, which was confirmed in both primary tumor and peritoneal dissemination. Of the four cases, acquired mutations of RAS, as well as BRAF V600E mutation, was detected in the blood obtained only after confirmation of acquiring resistance by radiological examinations.Conclusions: Our results suggest liquid biopsy based on the PCR-rSSO is a successful procedure for capturing acquired mutations with precise information of mutational spectrum that may lend us to reach selective target agents for RAS mutations.