Low-dose heparin prophylaxis reduces postoperative death from fatal pulmonary embolism and its long-term anti-cancer effect has now been assessed in a retrospective study of 1250 patients, 336 of whom (30%) underwent operation for cancer. There was a striking reduction in three year mortality amongst those patients who received low dose heparin compared to unteated controls (7.6% vs. 12.5%, P=0.005). Death from disseminated malignancy was halved (9.2% vs. 21.4%). The mechanism remains unclear, but may reflect either the antithrombotic actions of heparin or a direct antitumour cell effect.