Hiroaki Ikematsu

Objectives There are several types of colorectal cancer (CRC) according to the detection methods and intervals, including interval CRC (iCRC) and postcolonoscopy CRC (PCCRC). We aimed to examine their proportions and characteristics. Methods We conducted a multicenter prospective study using questionnaires in Japan (“C‐DETECT study”), in which differences in CRC characteristics according to detection methods and intervals were examined from consecutive adult patients. Because the annual fecal immunochemical test (FIT) was used in population‐based screening, the annual FIT‐iCRC was assessed. Results In total, 1241 CRC patients (1064 with invasive CRC) were included. Annual FIT‐iCRC (a), 3‐year PCCRC (b), and CRC detected within 1 year after a positive FIT with noncompliance to colonoscopy (c) accounted for 4.5%, 7.0%, and 3.9% of all CRCs, respectively, and for 3.9%, 5.4%, and 4.3% of invasive CRCs, respectively. The comparison among these (a, b, c) and other CRCs (d) demonstrated differences in the proportions of ≥T2 invasion ([a] 58.9%, [b] 44.8%, [c] 87.5%, [d] 73.0%), metastasis ([a] 33.9%, [b] 21.8%, [c] 54.2%, [d] 43.9%), right‐sided CRC ([a] 42.9%, [b] 40.2%, [c] 18.8%, [d] 28.6%), and female sex ([a] 53.6%, [b] 49.4%, [c] 27.1%, [d] 41.6%). In metastatic CRC, (a) and (b) showed a higher proportions of BRAF mutations ([a] [b] 12.0%, [c] [d] 3.1%). Conclusions Annual FIT‐iCRC and 3‐year PCCRC existed in nonnegligible proportions. They were characterized by higher proportions of right‐sided tumors, female sex, and BRAF mutations. These findings suggest that annual FIT‐iCRC and 3‐year PCCRC may have biological features different from those of other CRCs.