Recent developments in molecular-targeted therapies have improved the clinical outcome of cancer patients; however, the issue of adverse effects due to treatments has often gone unconsidered. We herein report the results of a clinical trial of dual genomic analyses for healthy longevity in a postoperative cancer patient. We performed dual genomic analyses for a representative 79-year-old rectal cancer patient who relapsed with liver metastasis. First, we determined single-nucleotide polymorphisms according to the constitution and disease risk in the genomic DNA from the patient's saliva by referring to the data of 10,000 Japanese patients obtained from Yahoo Japan Corporation. Second, we conducted whole-exome sequencing to detect druggable mutations in the primary tumour. Forty of 59 determinable characters related to the constitution were consistent with the clinical phenotype. Several diseases classified as 'high risk' diseases actually occurred during the patient's clinical course. Of the 129 significant mutations, we identified somatic mutations in BRAF, PIK3CA, and SMAD4 as targets. The dual genomic examination will improve the follow-up observation system to support primary care doctors in the social community for taking care of postoperative cancer patients.