A liver cyst is an abnormal sack filled with fluid and is not cancerous, while a cystic tumor may become malignant over time, according to the American Liver Foundation and Cleveland Clinic. Some liver cysts are caused by a parasite, but the cause of most liver cysts is not known.
While liver cysts only contain fluid, cystic tumors on the liver contain both fluid and solid matter, notes Cleveland Clinic. Most cystic tumors are benign, but all cystic tumors must be removed because there is a risk of malignancy.
Some people develop a condition called polycystic liver disease, which causes the formation of multiple cysts on or in the liver, states the American Liver Foundation. In some cases, the disease requires a liver transplant.