How does liver cancer affect the digestive system? (this is for a science project, i don't really have liver cancer)

Well, it kills...: There is cancer OF the liver and also many cancers wind up IN the liver. In both cases, there is loss of liver function and more of a problem is a blockage of flow of the bile. This goes the wrong way and bile pigments (bilirubin) goes sky high (obstructive jaundice). http://emedicine.medscape.com/article/187001-clinical fluid build up in the abdomen. Loss of appetite. Loss of liver proteins.

It most: likely won't affect the digestive system unless it causes biliary obstruction, or the involvement of the liver is so widespread that it results in liver failure.

Google it: I did and this is what I copied: Weight loss not associated with changes in diet. Decrease in appetite or a feeling of fullness after a small meal. Nausea and vomiting not associated with other known conditions. General weakness and/or fatigue that is persistent, ongoing weakness or fatigue. Fever that is unrelated to other conditions. Pain occurring in the upper abdomen on the right side or near the right shoulder blade. Enlarged liver (hepatomegaly) felt as a mass under the ribs on the right side. Enlarged spleen felt as a mass under the ribs on the left side. Abdominal swelling (ascites) or bloating in the abdomen can occur as a mass forms. Jaundice, which appears as yellowing of the skin and eyes. Jaundice occurs when the liver is not functioning properly.