Constant Hiccups???

My father in law (stage 4 colon with mets to liver and stomach) can't seem to stop having the hiccups. Does anyone know what this is caused from? He had these constantly after his colostomy and so we attributed it to that. He battled them off and on for about a month then, he quit having them. Well all of a sudden, they've returned. Any ideas or suggestions? The doctor perscribed something for them but I guess it doesn't always work. Thanks, Sharyn