The invention relates to an ultra-low molecular weight heparin with an average molecular weight of 2000 to 3000 Daltons, an anti-FXa activity of about 160 U/mg and an anti-Flla activity of about 2 U/mg, in particular semuloparin, for use as a prophylactic antithrombotic agent in cancer patients receiving chemotherapy for locally advanced solid tumors, wherein said use is accompanied by an improval of the survival of patients with locally advanced cancer of the lungs or with a venous thromboembolism risk score equal to or greater than 3.
