Risk factors associated with these thrombotic events included the hypercoagulable state of the patients, the cancer types, the catheter types, and the placement of the catheter tips in the superior vena cava. Some single-arm studies found that CVC inserted from the left subclavian veins led to more CVC-related thrombosis than those inserted from the right subclavian vein. However, for most right-handed patients, to place these implantable CVCs on the right side is inconvenient for daily life because vigorous exercise was then impossible. Besides, these single-arm studies could not well control the other potentially interfering factors, such as the operators, catheter location and cancer types.