Therefore, we plan a randomized observational study to explore whether the side of implantable CVCs was actually associated with the complication rates. Cancer patients who need implantable CVCs will be randomized to have the catheters implanted either in the left subclavian vein or the right subclavian. Patients who had breast cancer, mediastinal mass with the diameter > 6 cm, ECOG performance score >2, or those who were not able to receive a standing P-A view chest X-ray will be excluded. Patients who had other reasons that prevented the randomization will also be excluded. The catheter-related complications will be actively reported by the patients. We will also enforce the records of complications by chart reviews and regular telephone contacts.