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BACKGROUND &AIMS: Coloncancers that develop after a complete colonoscopy may be the result of"failure of colonoscopy" or rapid tumor growth. Tumors that developvia the mismatch repair gene pathway demonstrate rapid tumor growth. The aim ofthis study was to determine if interval colon cancers were more likely thannoninterval cancers to result from the loss of function of mismatch repairgenes and hence demonstrate microsatellite instability (MSI). METHODS: Wesearched our institution's cancer registry for interval cancers, defined ascolon cancers that developed within 5 years of a complete colonoscopy. These werefrequency matched in a 1:2 ratio by age and sex to patients with nonintervalcancers (defined as colon cancers diagnosed on a patient's first recordedcolonoscopy). Archived cancer specimens for all subjects were retrieved andtested for MSI. RESULTS: Of the 993 colon cancers diagnosed during the studyperiod, 51 (5.1%) were identified as an interval cancer, and 112 subjects withnoninterval cancer served as a comparison group. Study subjects were almost allmen. MSI was found in 30.4% of interval cancers compared with 10.3% ofnoninterval cancers (P = .003). After adjusting for age, interval cancers were3.7 times more likely to show MSI than noninterval cancers (95% confidenceinterval, 1.5-9.1). This association was strongest for tumors located in thedistal colon (odds ratio, 17.5; P = .008). No difference in TNM stage atdiagnosis, histologic type or grade, or 5-year survival was found betweengroups. CONCLUSIONS: Interval colon cancers were almost 4 times as likely asnoninterval colon cancers to be associated with mismatch repair genedysfunction. Leggil'articoloFull-textdisponibile per i soci AIGO !!!!