All known cancer-specific mutations are stored in a public database called the Catalogue of Somatic Mutations in Cancer (COSMIC) . Recent large-scale efforts to characterize cancer genomes, such as the international cancer genome consortium  and the cancer genome atlas , are assumed to have identified most mutations originating in primary tumors. However, 10 of the 12 variants identified in the healthy individuals were not cataloged in COSMIC. Tumor-specific mutations have biological activities, and their base positions should be restricted to hot spots. On the contrary, non-functional variants are likely to occur randomly. To handle this, we made the following two assumptions: 1) COSMIC includes all somatic mutations present in cancer tissues; 2) low-frequency entries in COSMIC may arise from artifacts such as DNA damage or PCR/sequencing errors. A recent report supports the appropriateness of the second assumption . Accordingly, we removed variants not cataloged in COSMIC (version 78) and single-entry variants, except variants in TP53. Since a larger number of somatic mutations have been cataloged for the coding region of TP53, a more stringent criterion was appropriate. Accordingly, we removed TP53 variants with less than 10 entries. Thus, of the 16 TP53 variants identified in patients with pancreatic cancer in the first data set, we removed five variants with no entry, one with a single entry, and three with 2–9 entries in COSMIC. This bioinformatic process was designated as the CV78 filter. The CV78 filter removed all variants present in the healthy individuals (Table 1, top). The sensitivity of the assay to detect pancreatic cancer patients, namely the fraction of variant-positive cancer patients, was decreased from 54.4% to 33.3% with the CV78 filter. Since insertion/deletion errors were uncommon in our results (one insertion and one deletion), we excluded them from the analysis.