Impact of time since diagnosis and mortality rate on cancer‐associated venous thromboembolism: the Scandinavian Thrombosis and Cancer (STAC) cohort

Essentials•Competing risk by death may lead to overestimation of venous thromboembolism (VTE) risk in cancers.•We assessed the risk of VTE in cancer with and without accounting for competing risk by death.•The risk of VTE was influenced by the mortality rate and the time since cancer diagnosis.•Competing risk by death should be taken into account when exploring VTE risk in cancer.AcknowledgementsK. G. Jebsen TREC is supported by an independent grant from Stiftelsen Kristian Gerhard Jebsen. The study used data from the Cancer Registry of Norway. The interpretation and reporting of these data are the sole responsibility of the authors, and no endorsement by the Cancer Registry of Norway is intended or should be inferred.Stiftelsen Kristian Gerhard JebsenSummary: BackgroundVenous thromboembolism (VTE) is a common complication in cancer, and studies have suggested that aggressive cancers create the highest risk of VTE. However, competing risk by death may result in overestimation of VTE risk in patients with cancers associated with high mortality. Therefore, we estimated the risk of VTE by cancer site, accounting for the differential mortality between cancers.MethodsThe Scandinavian Thrombosis and Cancer cohort included 144 952 participants followed from 1993–1997 to 2008–2012. Incidence rates, cause‐specific hazard ratios (HRs) and subdistribution HRs (SHRs) were assessed for overall cancer and by cancer site according to time intervals since cancer diagnosis.ResultsDuring follow‐up, 14 272 subjects developed cancer, and 567 had cancer‐related VTE. In cause‐specific analyses, the VTE risk was highest in the first 6 months after cancer diagnosis (HR 17.5, 95% confidence interval [CI] 15.1–20.3), and declined rapidly thereafter. However, when mortality was taken into account, the risk was similar in the periods 6 months before (SHR 4.8, 95% CI 3.6–6.4) and 6 months after (SHR 4.6, 95% CI 3.9–5.4) cancer diagnosis. The range of the 2‐year cumulative VTE incidence rates was substantially narrowed for all cancer sites after competing risk by death was taken into account (from 1–10% to 1–4%).ConclusionVTE risk by cancer site was influenced by the mortality rate and the time since cancer diagnosis. Our findings suggest that the cancer itself is a major contributor to VTE risk, and that competing risk by death should be taken into account when VTE risk in cancer is explored. Essentials•Competing risk by death may lead to overestimation of venous thromboembolism (VTE) risk in cancers.•We assessed the risk of VTE in cancer with and without accounting for competing risk by death.•The risk of VTE was influenced by the mortality rate and the time since cancer diagnosis.•Competing risk by death should be taken into account when exploring VTE risk in cancer.AcknowledgementsK. G. Jebsen TREC is supported by an independent grant from Stiftelsen Kristian Gerhard Jebsen. The study used data from the Cancer Registry of Norway. The interpretation and reporting of these data are the sole responsibility of the authors, and no endorsement by the Cancer Registry of Norway is intended or should be inferred.Stiftelsen Kristian Gerhard Jebsen •Competing risk by death may lead to overestimation of venous thromboembolism (VTE) risk in cancers.•We assessed the risk of VTE in cancer with and without accounting for competing risk by death.•The risk of VTE was influenced by the mortality rate and the time since cancer diagnosis.•Competing risk by death should be taken into account when exploring VTE risk in cancer. K. G. Jebsen TREC is supported by an independent grant from Stiftelsen Kristian Gerhard Jebsen. The study used data from the Cancer Registry of Norway. The interpretation and reporting of these data are the sole responsibility of the authors, and no endorsement by the Cancer Registry of Norway is intended or should be inferred.Stiftelsen Kristian Gerhard Jebsen Venous thromboembolism (VTE) is a common complication in cancer, and studies have suggested that aggressive cancers create the highest risk of VTE. However, competing risk by death may result in overestimation of VTE risk in patients with cancers associated with high mortality. Therefore, we estimated the risk of VTE by cancer site, accounting for the differential mortality between cancers. The Scandinavian Thrombosis and Cancer cohort included 144 952 participants followed from 1993–1997 to 2008–2012. Incidence rates, cause‐specific hazard ratios (HRs) and subdistribution HRs (SHRs) were assessed for overall cancer and by cancer site according to time intervals since cancer diagnosis. During follow‐up, 14 272 subjects developed cancer, and 567 had cancer‐related VTE. In cause‐specific analyses, the VTE risk was highest in the first 6 months after cancer diagnosis (HR 17.5, 95% confidence interval [CI] 15.1–20.3), and declined rapidly thereafter. However, when mortality was taken into account, the risk was similar in the periods 6 months before (SHR 4.8, 95% CI 3.6–6.4) and 6 months after (SHR 4.6, 95% CI 3.9–5.4) cancer diagnosis. The range of the 2‐year cumulative VTE incidence rates was substantially narrowed for all cancer sites after competing risk by death was taken into account (from 1–10% to 1–4%). VTE risk by cancer site was influenced by the mortality rate and the time since cancer diagnosis. Our findings suggest that the cancer itself is a major contributor to VTE risk, and that competing risk by death should be taken into account when VTE risk in cancer is explored.