Participants

The SPR is a nationwide register based on the national Information Network for Cancer Treatment IT-platform and located at the Regional Cancer Center, Stockholm-Gotland, Sweden. CD patients are included upon diagnosis; the coverage is around 95% based on the comparison of annual incidences between the SPR, and a recent nationwide Swedish study that found an annual incidence of 1.6 cases per million in Sweden between 1987 and 1995 (20). Data collected include date of diagnosis, radiological description of the tumor size, information about treatment (surgery, radiotherapy, pharmacological), and evaluation of biochemical remission. Besides at diagnosis, data are entered at 1, 5, 10, 15, and 20 years of follow-up and when surgery or radiotherapy is performed. Since the dates of clinical follow-up do not occur at exactly the same intervals in every patient, the following intervals are used in the register: 5-year follow-up, 2.5 to 7.5 years, and 10-year follow-up, 7.5 to 12.5 years. The end of follow-up was either set as date of death, date of emigration, or October 31, 2018 (last available data on drug dispenses). Since the registers used to assess psychiatric morbidity (see following discussion) were not started the same year as the SPR, the study population was adapted depending on type of analysis (Fig. 1).

Outline of the study and eligible patients for each analysis. Age is median (IQR) at diagnosis.

For each patient with CD, 4 controls matched for sex, age, and residential area, obtained from the Statistics Sweden’s Total Population Register, were included. Matching was performed on the date of diagnosis of CD. The controls were given “dummy dates” corresponding to the respective case to enable comparisons at each time point of follow-up. The Total Population Register was also used to identify any migration of the participants. At follow-up, a control corresponding to a deceased or emigrated CD case was removed.