Colorectal cancer after surveillance colonoscopy - False-negative examination or fast growth?

PURPOSE: Colonoscopy is the preferred method for colorectal cancer surveill ance of high-risk patients. Despite its high sensitivity, polyps or cancers may be undetected by colonoscopy and later attributed to an accelerated ad enoma-carcinoma sequence. This study assesses how the characteristics of co lorectal cancers found at intervals between surveillance relate to the aden oma-carcinoma sequence and its prevention. METHODS: The records of 557 pati ents with colorectal cancer that were diagnosed from January 1, 1990, to De cember 31, 1996, were reviewed to identify those patients who had prior col onoscopic surveillance within 60 months of their diagnosis. RESULTS: There were 29 (5.2 percent) patients who had one or more colonoscopies before dia gnosis of their colorectal cancer. Mean interval between diagnosis and prio r colonoscopy was 23 (range, 4-59) months. The distribution of cancers incl uded nine cecum, two ascending, three hepatic flexure, five transverse, one splenic flexure, three descending, two sigmoid, three rectum, and one anal canal. The mean tumor size was 4.4 cm for the cecum and 2.4 cm for all oth er locations. There were 7 Tis, 6 T1, 4 T2, and 12 T3 lesions. Six patients with T3 lesions had prior colonoscopies within 24 months of the diagnosis. Three of four patients with lymphatic metastases had tumors in the cecum. Twenty tumors (69 percent) were well or moderately differentiated. Mean fol low-up was 41 (range, 7-95) months with two local recurrences and two unrel ated deaths. CONCLUSIONS: Size, differentiation, and stage of colorectal ca ncer in addition to the interval to diagnosis suggest that the majority of cancers found during surveillance colonoscopy followed prior false-negative examinations. Because cecal landmarks are most constant, prior photographi c documentation may help to prove or disprove fast growth of cancers found in the cecum during surveillance colonoscopy.