INTRODUCTION: Venous thromboembolism (VTE) may be the first manifestation of cancer. We aimed at evaluating the performance of 18F-Fluorodesoxyglucose Positron-Emission Tomography/Computed Tomography (FDG PET/CT) for occult cancer screening in patients with unprovoked VTE.
METHODS: This was a pre-specified analysis of a systematic review and individual patient data meta-analysis including prospective studies assessing cancer screening in patients with unprovoked VTE. Sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of FDG PET/CT were calculated based on cancer diagnosis during a 1-year follow-up period.
RESULTS: Four studies were identified as using FDG PET/CT as part of their extensive screening strategy. Out of the 332 patients who underwent FDG PET/CT, the scan was interpreted as positive in 67 (20.2%), as equivocal in 27 (8.1%), and as negative in 238 (71.7%). Seventeen (5.1%) patients were diagnosed with cancer at inclusion or during the 12-month follow up period. All cancers were diagnosed at initial screening. Pooled sensitivity, specificity, NPV, and PPV were 87.3% (95% CI, 55.3 to 97.4), 70.2% (95% CI, 48.2 to 85.6), 98.9% (95% CI, 94.3 to 99.7), and 17.9% (95% CI, 8.5 to 33.6), respectively.
CONCLUSION: FDG PET/CT appears to have satisfactory accuracy indices for cancer diagnosis in patients with unprovoked VTE. In particular, it exhibits a very high negative predictive value and could be used to rule out the presence of an underlying occult malignancy in this setting.
There is, as the authors remark, equipoise around the use of screening for cancer among patients with unprovoked cancer. Equipoise needs to consider (1) the diagnotic efficacy of screening (2) its impact on clinical outcomes. This is a meta-analysis of FDG PET/CT results in 332 patients with apparently unprovoked VTE and negative results of basic cancer screening. PET results were positive in 20%, equivocal in 8% and negative in 72%. 5% of patents had cancer at inclusion or during 12 months follow-up. Negative predictive value of PET was 99%, so PET ruled out an occult cancer. The positive predictive value of 18% is a big concern; only 15 of 67 positive test patients had confirmed cancer within 12 months. 8% of equivocal test results is another. One wonders what a positive or equivocal test result does to quality of life or to cancer survival. Guidelines continue to recommend against extensive testing for cancer in patients with a first and apparently unprovoked VTE.