Splenic mast cell tumor is the most common splenic neoplasm in the cat. This disease is frequently metastatic, involving liver, lymph node, and bone marrow, with a peripheral mastocythemia. The treatment of choice is splenectomy, with surprisingly long survival times (mean of 12-19 months) considering the extent of metastatic disease. There are currently no proven chemotherapeutic options for cats, although recent research suggests CCNU may be useful post-operatively.