Aspects of participation in sigmoidoscopy screening for colorectal cancer

Sammanfattning: Colorectal cancer is an important health problem due to a high morbidity and mortality but it is curable at an early stage and is therefore ideal for screening. Population-based screening of the average risk population using fecal occult blood testing has been demonstrated to decrease mortality. We are waiting for the results of randomized controlled trials evaluating sigmoidoscopy as a screening method. A high participation rate is a prerequisite for a screening program to be effective. The aim of this thesis was to evaluate the feasibility of sigmoidoscopy screening in a Swedish population with regard to compliance, findings and experiences among participants, factors associated with non-participation and possible self-selection among people participating. We randomly selected two thousand men and women, aged 59-61, residing in the uptake areas of the University Hospitals of Uppsala and Lund, and invited them to a screening sigmoidoscopy. These individuals were randomized to being telephoned by a nurse to schedule an appointment or asked to call and make the appointment themselves. After the sigmoidoscopy, the participants were asked to describe their experiences in a questionnaire using VAS scales. Participants with a pathological finding were planned for a colonoscopy. To study background factors associated with non-participation, various registers were utilized to provide information on each individual’s gender, country of birth, marital status, education, income, hospital contacts, place of residence, distance to screening center, and cancer within the family. All invitees were followed-up for nine years by means of record linkages to the Cancer- and Cause of Death Register. Thirty-nine per cent (771/1986) participated. There was a statistically significant difference in participation between the centers (47% Uppsala, 30% Lund), but not between the methods of invitation. A total of 11% (88/771) underwent colonoscopy. Three subjects were found to have colorectal cancer and 46 (6%) had adenomas. Overall, the participants’ answers to questions regarding self-perceived anxiety or discomfort were skewed towards low values on the VAS scale. The experience of pain and other discomfort could be explained by long examination time and anxiety during the procedure. Male gender (OR=1.27, 95% CI 1.03-1.57, relative to female), unmarried or divorced (OR=1.69, 95% CI 1.23-2.30 and OR=1.49, 95% CI 1.14-1.95, respectively, relative to married) and having an income in the lowest tertile (OR=1.68, 95% CI 1.27-2.23, relative to highest tertile) was associated with non-participation. The incidence of specific cancer and mortality outcomes tended to be higher among non-participants (e.g. colorectal cancer incidence [IRR=2.2, 95% CI 0.8-5.9] and mortality from gastrointestinal cancer [MRR=4.7, 95% CI 1.1-20.7]), compared those who participated. Relative to the matching general population, there was an overall increased risk of the studied outcomes among nonparticipants and a decreased risk among participants. For example, there was a 40% decreased risk of mortality from cancer (SMR=0.6 [0.3 to 0.97]) and a 50% decreased risk of all-cause mortality (SMR=0.5 [0.3 to 0.7]) among the participants. Our results indicate that screening with sigmoidoscopy is feasible in colorectal cancer screening if, however, participation is not hindered by the sigmoidoscopy per se. Invitations must appeal to men, unmarried individuals and people with low socio-economic status. The higher incidences of specific cancers and mortality among non-participants may be related to selfselection. This self-selection could attenuate the cost-effectiveness of screening programs on a population level, but this effect could be counteracted by a high participation rate.