Anders Ekbom

BACKGROUND: The Swedish National Inpatient Register (IPR), also called the Hospital Discharge Register, is a principal source of data for numerous research projects. The IPR is part of the National Patient Register. The Swedish IPR was launched in 1964 (psychiatric diagnoses from 1973) but complete coverage did not begin until 1987. Currently, more than 99% of all somatic (including surgery) and psychiatric hospital discharges are registered in the IPR. A previous validation of the IPR by the National Board of Health and Welfare showed that 85-95% of all diagnoses in the IPR are valid. The current paper describes the history, structure, coverage and quality of the Swedish IPR. METHODS AND RESULTS: In January 2010, we searched the medical databases, Medline and HighWire, using the search algorithm "validat* (inpatient or hospital discharge) Sweden". We also contacted 218 members of the Swedish Society of Epidemiology and an additional 201 medical researchers to identify papers that had validated the IPR. In total, 132 papers were reviewed. The positive predictive value (PPV) was found to differ between diagnoses in the IPR, but is generally 85-95%. CONCLUSIONS: In conclusion, the validity of the Swedish IPR is high for many but not all diagnoses. The long follow-up makes the register particularly suitable for large-scale population-based research, but for certain research areas the use of other health registers, such as the Swedish Cancer Register, may be more suitable.

BACKGROUND: The risk of colorectal cancer is increased among patients with ulcerative colitis. The magnitude of this increase in risk and the effects of the length of follow-up, the extent of disease at diagnosis, and age at diagnosis vary substantially in different studies. METHODS: To provide accurate estimates of the risk of colorectal cancer among patients with ulcerative colitis, we studied a population-based cohort of 3117 patients given a diagnosis of ulcerative colitis from 1922 through 1983 who were followed up through 1984. RESULTS: Ninety-two cases of colorectal cancer occurred in 91 patients. As compared with the expected incidence, the incidence of colorectal cancer in the cohort was increased (standardized incidence ratio [ratio of observed to expected cases] = 5.7; 95 percent confidence interval, 4.6 to 7.0). Less extensive disease at diagnosis was associated with a lower risk; for patients with ulcerative proctitis, the standardized incidence ratio was 1.7 (95 percent confidence interval, 0.8 to 3.2); for those with left-sided colitis, 2.8 (95 percent confidence interval, 1.6 to 4.4); and for those with pancolitis (extensive colitis, or inflammation of the entire colon), 14.8 (95 percent confidence interval, 11.4 to 18.9). Age at diagnosis and the extent of disease at diagnosis were strong and independent risk factors for colorectal cancer. For each increase in age group at diagnosis (less than 15 years, 15 to 29 years, 30 to 39 years, 40 to 49 years, 50 to 59 years, and greater than or equal to 60 years), the relative risk of colorectal cancer, adjusted for the extent of disease at diagnosis, decreased by about half (adjusted standardized incidence ratio = 0.51; 95 percent confidence interval, 0.46 to 0.56). The absolute risk of colorectal cancer 35 years after diagnosis was 30 percent for patients with pancolitis at diagnosis and 40 percent for those given this diagnosis at less than 15 years of age. CONCLUSIONS: Close surveillance and perhaps even prophylactic proctocolectomy should be recommended for patients given a diagnosis of pancolitis, especially those who are less than 15 years of age at diagnosis.

A substantial excess risk of lymphomas and nonmelanoma skin cancer has been demonstrated following organ transplantation. Large sample size and long follow-up time may, however, allow more accurate risk estimates and detailed understanding of long-term cancer risk. The objective of the study was to assess the risk of cancer following organ transplantation. A nationwide cohort study comprising 5931 patients who underwent transplantation of kidney, liver or other organs during 1970-1997 in Sweden was conducted. Complete follow-up was accomplished through linkage to nationwide databases. We used comparisons with the entire Swedish population to calculate standardised incidence ratios (SIRs), and Poisson regression for multivariate internal analyses of relative risks (RRs) with 95% confidence intervals (CI). Overall, we observed 692 incident first cancers vs 171 expected (SIR 4.0; 95% CI 3.7-4.4). We confirmed marked excesses of nonmelanoma skin cancer (SIR 56.2; 95% CI 49.8-63.2), lip cancer (SIR 53.3; 95% CI 38.0-72.5) and of non-Hodgkin's lymphoma (NHL) (SIR 6.0; 95% CI 4.4-8.0). Compared with patients who underwent kidney transplantation, those who received other organs were at substantially higher risk of NHL (RR 8.4; 95% CI 4.3-16). Besides, we found, significantly, about 20-fold excess risk of cancer of the vulva and vagina, 10-fold of anal cancer, and five-fold of oral cavity and kidney cancer, as well as two- to four-fold excesses of cancer in the oesophagus, stomach, large bowel, urinary bladder, lung and thyroid gland. In conclusion, organ transplantation entails a persistent, about four-fold increased overall cancer risk. The complex pattern of excess risk at many sites challenges current understanding of oncogenic infections that might become activated by immunologic alterations.