PURPOSE: This observational multi-phase trial is studying how well polymerized (cross-linked) sucralfate malate paste (ProThelial) works to prevent and treat mucositis in adult patients who are to receive or have received chemo/radiation therapy that have caused or is anticipated to cause mucositis in the oral cavity, esophagus, stomach, small or large intestine. The Phase IV study addresses prevention and treatment in the oral cavity. The Phase I study addresses prevention and treatment in the esophagus, stomach, small and large intestine.