Tumour necrosis factor (TNF) was originally described as a circulating factor that can induce haemorrhagic necrosis of tumours. It is now clear that TNF has many different functions in cancer biology. In addition to causing the death of cancer cells, TNF can activate cancer cell survival and proliferation pathways, trigger inflammatory cell infiltration of tumours and promote angiogenesis and tumour cell migration and invasion. These effects can be explained by the diverse cellular responses TNF can initiate through distinct signal transduction pathways, opening the way for more selective targeting of TNF signalling in cancer therapy. Copyright © 2013 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.