Maintenance treatment with azathioprine in ulcerative colitis: outcome and predictive factors after drug withdrawal. by Cassinotti, A, Actis, G, Duca, P, Massari, A, Colombo, E, Gai, E, Annese, V, D'Albasio, G, Manes, G, Travis, S, Porro, G, Ardizzone, S