Abstract: No new studies were identified for this 2018 update. In total, four studies with 1644 participants are included. Two studies assessed the effect of extensive tests including computed tomography (CT) scanning versus tests at the physician's discretion, while the other two studies assessed the effect of standard testing plus positron emission tomography (PET)/CT scanning versus standard testing alone. For extensive tests including CT versus tests at the physician's discretion, the quality of the evidence, as assessed according to GRADE, was low due to risk of bias (early termination of the studies). When comparing standard testing plus PET/CT scanning versus standard testing alone, the quality of evidence was moderate due to a risk of detection bias. The quality of the evidence was downgraded further as detection bias was present in one study with a low number of events. When comparing extensive tests including CT versus tests at the physician's discretion, pooled analysis on two studies showed that testing for cancer was consistent with either benefit or no benefit on cancer-related mortality (odds ratio (OR) 0.49, 95% confidence interval (CI) 0.15 to 1.67; 396 participants; 2 studies; P = 0.26; low-quality evidence). One study (201 participants) showed that, overall, malignancies were less advanced at diagnosis in extensively tested participants than in participants in the control group. In total, 9/13 participants diagnosed with cancer in the extensively tested group had a T1 or T2 stage malignancy compared to 2/10 participants diagnosed with cancer in the control group (OR 5.00, 95% CI 1.05 to 23.76; P = 0.04; low-quality evidence). There was no clear difference in detection of advanced stages between extensive tests versus tests at the physician's discretion: one participant in the extensively tested group had stage T3 compared with four participants in the control group (OR 0.25, 95% CI 0.03 to 2.28; P = 0.22; low-quality evidence). In addition, extensively tested participants were diagnosed earlier than control group (mean: 1 month with extensive tests versus 11.6 months with tests at physician's discretion to cancer diagnosis from the time of diagnosis of VTE). Extensive testing did not increase the frequency of an underlying cancer diagnosis (OR 1.32, 95% CI 0.59 to 2.93; 396 participants; 2 studies; P = 0.50; low-quality evidence). Neither study measured all-cause mortality, VTE-related morbidity and mortality, complications of anticoagulation, adverse effects of cancer tests, participant satisfaction or quality of life. When comparing standard testing plus PET/CT screening versus standard testing alone, standard testing plus PET/CT screening was consistent with either benefit or no benefit on all-cause mortality (OR 1.22, 95% CI 0.49 to 3.04; 1248 participants; 2 studies; P = 0.66; moderate-quality evidence), cancer-related mortality (OR 0.55, 95% CI 0.20 to 1.52; 1248 participants; 2 studies; P = 0.25; moderate-quality evidence) or VTE-related morbidity (OR 1.02, 95% CI 0.48 to 2.17; 854 participants; 1 study; P = 0.96; moderate-quality evidence). Regarding stage of cancer, there was no clear difference for detection of early (OR 1.78, 95% 0.51 to 6.17; 394 participants; 1 study; P = 0.37; low-quality evidence) or advanced (OR 1.00, 95% CI 0.14 to 7.17; 394 participants; 1 study; P = 1.00; low-quality evidence) stages of cancer. There was also no clear difference in the frequency of an underlying cancer diagnosis (OR 1.71, 95% CI 0.91 to 3.20; 1248 participants; 2 studies; P = 0.09; moderate-quality evidence). Time to cancer diagnosis was 4.2 months in the standard testing group and 4.0 months in the standard testing plus PET/CT group (P = 0.88). Neither study measured VTE-related mortality, complications of anticoagulation, adverse effects of cancer tests, participant satisfaction or quality of life. Specific testing for cancer in people with unprovoked VTE may lead to earlier diagnosis of cancer at an earlier stage of the disease. However, there is currently insufficient evidence to draw definitive conclusions concerning the effectiveness of testing for undiagnosed cancer in people with a first episode of unprovoked VTE (DVT or PE) in reducing cancer- or VTE-related morbidity and mortality. The results could be consistent with either benefit or no benefit. Further good-quality large-scale randomised controlled trials are required before firm conclusions can be made.

Plain-language summary: This review assessed whether testing for undiagnosed cancer in people with a first unprovoked VTE (DVT or PE) was effective in reducing cancer and VTE-related illness and death. We found four studies with 1644 participants (current to July 2018). Two studies compared extensive cancer tests with tests carried out at the physician's discretion and two studies compared cancer tests plus scanning with cancer tests alone. Combining the results of the two studies showed that extensive testing had no effect on the number of cancer-related deaths. Additionally, extensive testing did not identify more people with cancer. However, extensive testing did identify cancers at an earlier stage (approximately 10 months earlier) and cancers were less advanced in people in the extensive testing group than in people in the group with tests carried out at the physician's discretion. Neither study looked at the number of deaths due to any cause, deaths and illness associated with VTE, side effects of cancer tests, side effects of VTE treatment or participant satisfaction. Two studies that compared tests plus scanning with tests alone showed that adding computed tomography scanning had little or no effect on the number of deaths, cancer-related deaths, illness associated with VTE; nor did it identify more people with cancer, or show a clear difference in time to diagnosis or stages of cancer diagnosed. Neither study looked at deaths associated with VTE, side effects of cancer tests, side effects of VTE treatment, participant satisfaction or quality of life. When comparing extensive tests versus tests at the physician's discretion, the quality of the evidence was low due to bias caused by two of the studies stopping early. When comparing tests plus PET/CT scanning with tests alone, the quality of the evidence ranged from low to moderate due to imprecision caused by a low number of events and bias due to lack of blinding of people assessing the effects. This review found that there are too few trials to determine whether testing for undiagnosed cancer in people with a first unprovoked VTE (DVT or PE) is effective in reducing cancer and VTE-related deaths and illness. Further good-quality and large-scale studies are required.