This study is being done to determine whether a substance called hematoporphyrin can be used to treat tumors in various locations in the body when used in association with a laser. Hematoporphyrin is a substance that is taken up by cancerous cells. When these cells are exposed to the energy emitted by a laser source, chemical reactions occur in the cell and cause the cells to die. It is hoped that this treatment method may be able to selectively destroy malignant cells without damaging surrounding healthy tissue.