AbstractsMedical & Health Science

The association between cancer and venous thromboembolism (VTE) was described already in the 19th century and cancer has later been acknowledged as one of the most important risk factors for VTE. Population-based studies on the subject with information about confounders and validated endpoints are lacking. The first aim of this thesis was to estimate the frequency of VTE among cancer patients in a population-based cohort study and assess the risk among cancer patients compared to a cancer-free reference population. Secondly, we wanted to investigate whether the level of leukocytes and platelets at inclusion influenced the future risk of VTE in cancer patients and in those who remained cancer-free. The fourth survey of the Tromsø study (Tromsø IV) was applied in all four papers of this thesis. The Tromsø Study is a prospective study of adult inhabitants of Tromsø. In Tromsø IV (1994-95), information from more than 27 000 subjects were collected by physical examination, self-administrated questionnaires and blood tests, and VTE events were registered throughout 2010. Information about cancer was provided by the Cancer Registry of Norway. In paper II, the Tromsø IV cohort was merged with two additional Scandinavian cohorts (i.e. HUNTII and DCH) and 137 000 subjects were included in the study. VTE occurred among 3-5 % of the cancer patients. Malignancy accounted for 20-25 % of the VTE events in the population, and the proportion was highest among middle-aged where cancer explained almost 30 % of the events. Patients with malignancy exhibited an overall 5-fold increased risk of VTE. The risk was highest during the initial 6 months after diagnosis (i.e. 17-fold increased) and declined thereafter. Patients with certain cancers, such as pancreatic-, lung- and brain cancers, had a particularly high risk of VTE. However, most cancers exhibited a high risk during the initial 6 months after diagnosis with incidence rates ranging from 30-90 cases per 1000 person-years for all sites, except for breast- and prostate cancers which had substantially lower risks. Despite the strong association between high age and VTE in the general population, the risk of VTE was similar across age-categories within the first year after a cancer diagnosis. We found that WBC- and platelet count were associated with VTE in cancer patients. Baseline leukocyte- or platelet count above the 80th percentile provided doubled risk of VTE compared to the 40th percentile, and the combined effect of the parameters was synergistic. The association was confined to subjects diagnosed with cancer, and the results suggest that platelet- and white blood cell counts have impact on the risk of cancer-related VTE.; Sammenhengen mellom kreft og venøs blodpropp (i.e. VTE) ble beskrevet allerede på 1800-tallet, og i dag er kreft en av de viktigste risikofaktorene for VTE vi kjenner til. Store befolkningsstudier med informasjon om tilleggsfaktorer og validerte diagnoser har manglet i kunnskapsbildet. Vi ønsket å undersøke forekomsten av kreft-relatert VTE i en…