Much has happened in the field of cancer research and treatment over the last decades, and the knowledge of cancer biology has increased tremendously. Today it is fair to say that cancer is no longer enigmatic, but it is still incredibly complicated. This review presents an update on the current knowledge of the molecular background of cancer and highlights new information about common characteristics of the malignant phenotype. The local tumour microenvironment including blood vessels plays an active role in the development and progression of cancer, by recently discovered mechanisms involving inflammatory cells as well as hypoxia and the interstitial fluid pressure.