Background/Aim: Synchronous colorectal cancer, which occurs in approximately 4.8-8.4% of all colorectal cancers, has a genetic profile with a higher rate of v-raf murine sarcoma viral oncogene homolog B1 (BRAF) mutation and microsatellite instability-high than solitary colorectal cancer. However, little information is available on heterogeneity among tumor lesions because of difficulty in performing genetic tests in all lesions in clinical practice. Case Report: A 44-year-old man presented with multiple recurrent lung metastases 42 months after the endoscopic resection of early stage synchronous ascending and sigmoid colon cancers. The genetic testing of sigmoid colon cancer tissue samples, their state being more advanced than that of ascending colon cancer, revealed a v-Ki-ras 2 Kirsten rat sarcoma viral oncogene homolog mutation (G13C) and BRAF wild type. However, the tumor was refractory to initial chemotherapy and rapidly progressed to new liver metastases. Therefore, we suspected that there may be biological heterogeneity between the primary sigmoid colon lesion and liver metastases. Next, we performed next-generation sequencing on circulating tumor DNA from the patient's plasma (Foundation One Liquid CDx Conclusion: Genetic profiling with liquid biopsy at the time of recurrence and metastasis may be useful in patients with multiple synchronous cancers because there is less heterogeneity between primary and metastatic sites.