The study population was retrieved from the Swedish Colon and Rectal Cancer Register (SCRCR). The study included all patients with rectal cancer operated on by anterior resection with a defunctioning stoma between 1 January 2007 and 31 December 2013.
Since 1995, all patients diagnosed with an adenocarcinoma of the rectum in Sweden are registered in the SCRCR. Data are reported to the register by the surgeons and pathologists involved and the register’s national coverage is 99% . The register has been validated and shown to be of high quality .
Data from the SCRCR include information on patient characteristics, preoperative workup, procedural details (including whether a defunctioning stoma was created), tumour characteristics, complications, planned oncologic therapy, effected oncologic treatment and follow-up results (e.g. local recurrence, metastases, late complications, stoma reversal, death). Since January 2011, postoperative complications are not only registered according to type, but also classified according to the Clavien-Dindo classification; this information is not available for procedures prior to 2011. Data were retrieved from the SCRCR on 12 May 2016.
To confirm that information regarding date of stoma reversal was complete, data from the Swedish National Patient Register (NPR) were also retrieved. Since 1987, the NPR includes data on all inpatient care in Sweden, and it is mandatory for Swedish health providers (county councils) to report all inpatient data to the NPR. Coverage of the NPR register has been estimated to be more than 99% and validity is high . All data on inpatient care of patients in the study population including records of stoma reversal (using the Swedish Classification of Surgical and Medical Procedures) were obtained.
Socioeconomic data on income and level of education at the time of cancer surgery were obtained from Statistics Sweden, the administrative agency responsible for developing, producing and distributing official statistics and other governmental statistics. Statistics Sweden also provided data on if and when patients in the study group had emigrated or died.
The outcomes investigated were reversal of stoma within a latest expected time to closure (yes/no) and time to reversal of stoma. “Latest expected time to closure” was defined as within 9 months of stoma creation in patients who did not receive adjuvant chemotherapy, and 1 year from stoma creation in patients who were planned for adjuvant chemotherapy. The time limit of 9 months was chosen considering a median time to closure of over 6 months. Ongoing adjuvant chemotherapy is usually a contraindication to stoma reversal; therefore, the time span allowed for patients who received adjuvant chemotherapy was extended for 3 months (and the limit set to 1 year). Time to reversal of stoma was evaluated over a follow-up period of one and a half years following creation of stoma.
Statistical analyses were performed using Stata/SE 12.1 (StataCorp, College Station, TX, USA). Uni- and multivariable logistic regression analyses were performed to detect factors associated with reversal of the loop-ileostomy during the study period. Factors assessed were age, sex, ASA physical status classification, cancer stage according to the TNM classification system, postoperative complication (yes/no), adjuvant chemotherapy, low economic standard (disposable income below 60% of the median income of the entire population; yes/no) and level of education (primary or lower secondary education/upper secondary education/post-secondary education). Possibly, determining factors for the multivariable analysis were selected based on univariable analysis and on hypothesised relevance. A multivariable Cox proportional hazard regression model was used to estimate the hazard rates regarding time from the construction to the reversal of the stoma for the investigated factors. The same factors as in the logistic regression were investigated. Possibly, determining factors for the multivariable analysis were selected based on univariable analysis.