Li, F., Wang, F., Yang, X., Ji, D., Li, J., Wang, N., Liu, Y., Li, C., Zhang, T. and Li, K. (2012) Covered Stents versus Uncovered Stents for the Palliation of Malignant Extrahepatic Biliary Obstruction Caused by Direct Tumor Invasion: A Cohort Comparative Study. Medical Oncology, 29, 2762-2770.