BACKGROUND Clonal hematopoiesis is the production of a specific single clonal type of cell in the blood and is often found in cancer genomic profiling tests. When the clone carries a pathogenic variant, it may be important to differentiate between somatic or germline origin. The variant in the blood that has a lower minor allele frequency could reflect heterozygous germline origin, somatic mosaicism, and clonal hematopoiesis. It is important to evaluate suspected variants to determine the course of treatment and follow-up of the patient, depending on the patient's medical condition and family situation. CASE REPORT We report a 53-year-old Japanese man with gastric cancer who underwent a cancer genomic profiling test searching for therapeutic agents. The profiling test detected a variant, TP53 c.559+2T>G minor allele frequencies of 9% (168/1865) in tumor tissue and 29.1% (58/199) in paired blood. Since the TP53 variant has the possibility of Li-Fraumeni syndrome, ancillary testing was performed using fingernails, buccal swab, and blood specimens. The genomic analysis revealed no TP53 variant in his fingernails. The patient had previously received platinum-based chemotherapies, suggesting that the variant reflected treatment-induced clonal hematopoiesis. CONCLUSIONS Identifying clonal hematopoiesis when performing genomic profiling tests for patients with cancer is important. Examining multiple tissues to determine whether a variant arises from clonal hematopoiesis or is of germline origin can provide more accurate genetic information and improve patient follow-up care.