“While earlier linked data have shown sociodemographic disparities in survival and surgical mortality for colorectal cancer, research into effects of colonoscopy surveillance on colorectal cancer outcomes has been limited in Australia. This study uses colorectal cancer data for South Australia to examine associations between pre-diagnostic colonoscopy and survival,” stated the study authors.
The researchers, whose work appeared in BMC Cancer, used linked Medical Benefits Schedule (MBS) claims, hospital-inpatient, and cancer-registry data to gather colonoscopy data on colorectal cancer patients diagnosed between 2003 and 2013. Data included colonoscopy year, number of examinations, and the time from index colonoscopy to cancer diagnosis. Having numerous colonoscopies and exposures of more than one year from the initial colonoscopy to diagnosis were considered indicators of screening or surveillance activity. Colonoscopies that took place within one year of cancer diagnosis were considered more likely to be a response to cancer symptoms compared to colonoscopies conducted one year or earlier prior to cancer diagnosis. Sub-hazard ratios (SHRs) from competing risk regression were used to evaluate the relationship between colonoscopy history and post-diagnostic survival, adjusting for sociodemographic and cancer characteristics.
Final analysis included 12,906 colorectal cancer patients (mean age, 70.2 years; 54% were male), of whom 37% (n = 4,712) had a pre-diagnostic colonoscopy. Patients with a pre-diagnostic colonoscopy, compared to those without, tended to be older at diagnosis and were more likely to live in socioeconomically disadvantaged areas; 76% had one colonoscopy, 16% had two, and 8% had three or more (maximum was 11). The mean time between initial colonoscopy and cancer diagnosis was 1.5 years. Among patients with a pre-diagnostic colonoscopy, most (63%) received their cancer diagnosis within one year of the initial colonoscopy.
In the total cohort, 29% of patients died from colorectal cancer, and 13% died due to other causes. In unadjusted analyses, there was a correlation between pre-diagnostic colonoscopy and a 17% reduced risk in colorectal cancer death (SHR, 0.83; 95% confidence interval [CI], 0.78–0.89). when adjusting for time period and sociodemographic characteristics, colorectal cancer mortality risk reduced by 17% for one pre-diagnostic colonoscopy examination, 27% for two pre-diagnostic colonoscopy examinations, and 45% for three or more pre-diagnostic colonoscopy examinations. Patients with more than one year from first colonoscopy during the study period to diagnosis, compared to those with less than one year, had a 17% reduced risk of death. When adjusting for less advanced cancer, these reductions were “significantly reduced or eliminated.”
The authors wrote in their conclusion, “The reduced risk of colorectal cancer death with multiple colonoscopy examinations, and longer time from first colonoscopy examination, is indicative of a benefit from screening or surveillance of high-risk patients, since it would largely exclude colonoscopies undertaken close to cancer diagnosis in response to symptoms.”