The blackening of blood vessels after chemotherapy for lung cancer may be caused by drug stimulation of blood vessel wall or considered to be caused by phlebitis. 1. Drug stimulation: patients with lung cancer can choose chemotherapy under doctor’s guidance. As chemical drugs are more stimulating, when long-term chemotherapy is used, patients will have blackened blood vessels. 2. Phlebitis: when infusion is improper and stimulating drugs, all of them may lead to trauma of blood vessels and cause aseptic inflammation of veins. Blackening of blood vessels after chemotherapy for lung cancer may be caused by phlebitis due to stimulation of chemical drugs. Patients will have local vascular hyperpigmentation and accompanied by pain, redness and swelling of skin, and hard nodules can be touched locally. There are many reasons causing blackening of blood vessels after chemotherapy for lung cancer, and it is suggested that patients should go to regular hospitals in time to have relevant examination so as to find out the causes of the disease.