Interferon (IFN)-α, on paper, should be quite effective against hepatocellular carcinoma, the most frequent form of primary liver cancer. IFN-α can suppress tumor growth directly by acting on tumor cells, as well as indirectly by activating cytotoxic CD8+ T cells. In addition, it can slow replication of hepatitis B virus, which is involved in 50% to 80% of cases of hepatocellular carcinoma. However, IFN-α on its own has performed disappointingly in clinical trials.