Tumour blood supply and lymphocytes. Coloured scanning electron micrograph (SEM) of a section through a malignant (cancerous) tumour, showing the cancer cells (red), the blood vessels (brown) that supply it, tumour-infiltrating lymphocytes (TILs, white) and connective tissue (collagen, grey). The blood supply has grown by the release of chemicals from the tumour that encourage new blood vessel growth (angiogenesis). TILs are white blood cells (lymphocytes) that have left the bloodstream and migrated towards a tumour. The presence of TILs increases the success of immunotherapy for cancer. Magnification: x1000, when printed 15 centimetres wide.