Serum-Based KRAS(G12/G13) Mutation Detection Using Droplet Digital PCR: Clinical Implications and Limitations in Colorectal Adenocarcinoma With Tumor Heterogeneity

BACKGROUND: Cell-free DNA (cfDNA) has arisen as an alternative target for evaluating somatic mutations in cancer. KRAS mutation status is critical for targeted therapy in colorectal adenocarcinoma (CRAC). We evaluated KRAS(G12/G13) mutations in cfDNA extracted from serum and compared the results with KRAS(G12/G13) mutations detected in tissue samples. We assessed the clinical significance of KRAS(G12/G13) mutation in serum in regard to recurrence and metastasis of CRAC. METHODS: A total of 146 CRAC patients were enrolled, and KRAS(G12/G13) mutations were evaluated in 146 pairs of serum and tissue samples. In addition, 35 pairs of primary and metastatic CRAC tissue samples were evaluated for KRAS(G12/G13) mutational status. RESULTS: Detection of KRAS(G12/13) mutation from serum and tissue had a 55% concordance rate, and serum detection had a sensitivity of 39.8%. Detection of the KRAS(G12/13) mutation yielded a 14% discordance rate between primary and metastatic tissue. CRAC patients with mutant KRAS(G12/13) mutation in serum but wild-type KRAS(G12/13) in tissue had concurrent KRAS(G12/13)-mutant metastatic tumors, indicating spatial genetic heterogeneity. Changes in serum KRAS(G12/G13) mutation status during postoperative follow-up were associated with recurrence. Conclusion: Although serum detection of the KRAS(G12/13) mutation cannot substitute for detection in tissue, serum testing can support the interpretation of a CRAC patient’s status in regard to concurrent metastasis. Dynamic changes in serum KRAS(G12/13) mutation status during follow-up indicated that cfDNA from serum represents a potential source for monitoring recurrence in CRAC patients.