SOURCE: A registry-based prediction model for overall survival in patients with metastatic oesophageal or gastric cancer by Van Den Boorn, HG, Abu-Hanna, A, Veer, E, Van Kleef, JJ, Lordick, F, Stahl, M, Ajani, JA, Guimbaud, R, Park, SH, Dutton, SJ, Bang, Y-J, Boku, N, Mohammad, NH, Sprangers, MAG, Verhoeven, RHA, Zwinderman, AH, Van Oijen, MGH, Van Laarhoven, HWM