Chemotherapy-associated clonal hematopoiesis mutations should be taken seriously in plasma cell-free DNA KRAS/NRAS/BRAF genotyping for metastatic colorectal cancer.

BACKGROUND

Genotyping of plasma cell-free DNA (cfDNA) is an increasingly important method to assess the tumor mutation status in colorectal cancer (CRC) patients. Clonal hematopoiesis (CH) releases non-tumor somatic mutations into blood, causing false positive results in cfDNA-based tumor genotyping. It is still not clear if CH should be examined in all CRC patients undergoing cfDNA analysis.

METHODS

We analyzed cfDNA KRAS, NRAS and BRAF genotypes in 236 metastatic CRC patients, who had matched tissue genotyping results, by next-generation sequencing using plasma cfDNA. The cfDNA-only mutations with allele frequencies (AFs) < 5% were highly suspicious for being CH-derived mutations. The origins of cfDNA mutations were confirmed by droplet digital polymerase chain reaction (ddPCR) using paired peripheral blood cells (PBCs) and CH-derived mutations were finally determined. One patient with a CH-derived mutation was followed up and the subpopulation of blood cells, in which CH was present, was investigated.

RESULTS

Three CH-derived mutations, KRAS Q61H, KRAS G12D and KRAS G12V, were identified in the patient cohort. All three patients harboring corresponding CH-derived mutations had a prior chemotherapy history. The CH-derived KRAS G12V mutation in a patient was found only present in lymphocytes and persisting under treatment. For all cfDNA mutations, the CH-derived ones were clustered in the patients with < 5% mutation AF and prior chemotherapy.

CONCLUSION

The prevalence of CH in CRC patients was limited, and prior chemotherapy was a contributing factor of CH. It is recommended for patients with < 5% mutation AF and prior chemotherapy to have genotyping analysis of their PBCs following plasma cfDNA genotyping.