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NO INCREASED INCIDENCE OF RIGHT-SIDED COLORECTAL CANCERS AFTER BREAST AND OTHER GYNECOLOGICAL CANCERS – A POPULATION-BASED ANALYSIS
L Tang, Z Nugent, A Demers, H Singh
Departments of Gastroenterology and Community Health Sciences, University of Manitoba and CancerCare Manitoba, Winnipeg, Manitoba
Purpose: Hormonal influences may be responsible for women having a higher incidence of right-sided colorectal cancers (CRCs). They are also involved in the development of breast and other gynecological (ovarian and endometrial) cancers. No previous study has evaluated the risk of right-sided CRC after breast and other gynecological cancers. Increased incidence of right-sided CRC may justify a preference for CRC screening by colonoscopy. Our aim was to determine the incidence of right-sided CRC after the diagnosis of gynecological cancers.
METHODS: All cases of breast, endometrial, and ovarian cancers diagnosed between 1956 and 2005 were identified from the Manitoba Cancer Registry and followed-up until diagnosis of CRC, death or migration from the province, or until the completion of the study. Age-standardized incidence ratios (SIRs) for all CRCs and right-sided CRCs (cecum, ascending colon and hepatic flexure) were calculated to compare the observed CRC incidence to that expected in the general population. Stratified analysis was performed to determine the risk after different durations of follow-up (<1 year, 1-5 years, 5-10 years, >10 years) after the primary cancer diagnosis with statistical significance set at p<0.05.
RESULTS: There were 32,568 cases of breast, endometrial or ovarian cancers diagnosed between 1956 and 2005. The SIR for all CRCs was 1.01 (95% CI 0.93-1.09) and for right-sided CRC was 1.07 (95% CI 0.94-1.22) following gynecological cancer diagnosis. This risk did not change in the more recent years; SIR for right-sided CRCs, after primary cancer diagnosis between 1985 and 2005, was 1.19 (95%CI 0.96-1.47). The SIRs remained non-significant for different durations of follow-up; <1 year 1.05, 1-5 years 1.38, 5-10 years 1.11 and >10 years 1.08.
CONCLUSIONS: There is no increase in the overall risk for CRC or for right-sided CRC after the diagnosis of breast, endometrial or ovarian cancer. CRC screening strategy, after the diagnosis of a gynecological cancer, should be similar to that for the general population.