Treatment of cancer is a double-edged sword: it should be as aggressive as possible to completely destroy the tumour, but it is precisely this aggressiveness which often causes severe side effects - a reason why some promising therapeutics can not be applied systemically. In addition, therapeutics such as cytokines that physiologically function in a para- or autocrine fashion require a locally enhanced level to exert their effect appropriately. An elegant way to accumulate therapeutic agents at the tumour site is their conjugation/fusion to tumour-specific antibodies. Here, we discuss recent preclinical and clinical data for antibody-drug conjugates and fusion proteins with a special focus on drug components that exert their antitumour effects through normal biological processes.