Interferon (IFN) was the first cytokine produced by recombinant DNA technology used in wide-spread clinical treatment of infectious diseases as well as malignancies. The IFN clinical potential was clearly realized from the outset. However, IFN represents one of the most controversial drugs of our time, as remarkable cycles of promise and disappointment have affected its development and use. Considerable evidence regarding anti-tumor activities of IFNs has been reported. In this paper we focus on molecular bases of the IFN system that may relate to its antitumor activities. Many of the numerous genes transcriptionally activated by IFNs have been shown to encode proteins that activate immune recognition of tumor cells, directly or indirectly exert tumor suppressor activity and/or control tumor cell cycle and programmed cell death. In addition, a physiological relevant function for endogenous type I IFN in cancer immunoediting process and a new way to IFN clinical use based on gene therapy or vaccine-like approaches have recently been suggested. The identification of selected tissue-specific and/or tumor-specific target pathways as well as of different type I IFN tumor escape and resistance mechanisms may provide novel approaches in the search for new IFN-based therapeutic strategies to circumvent cancer disease or improve clinical outcome. Promising IFN treatment has been recently defined by using novel pharmaceutical preparations with a more favourable pharmacokinetic response, also in combination with other bioreagents or other modalities of therapy. Translational research, linking both basic and clinical research, will lead to a new rationale for the use of IFN in cancer therapy.