Temozolomide is a novel derivative of the oral dialkylating agent imidazotetrazine, which is rapidly converted to the active product MTIC (3-methyl-(triazine-1-)imidazole-4-carboxamide) in the physiological pH state of the body circulation.The cytotoxic effect of MTIC is mainly manifested by alkylation on the oxygen atom of guanine at position 6 on the DNA molecule and alkylation of the nitrogen atom at position 7, which exerts its cytotoxic effect through methylation adducts A phase II clinical study by Pietanza et al. investigated the efficacy of temozolomide in relapsed small cell lung cancer. 64 patients were enrolled, including 48 patients with sensitive recurrence and 16 patients with refractory disease. Sixteen patients with refractory disease were given temozolomide 75 mg/m2/d for 21 days in a 28-day cycle. As a result, an objective remission rate of 23% was achieved, while for patients with brain metastases, 38% of patients achieved stabilization or reduction of intracerebral lesions. In the update of the NCCN 2013 2nd edition small cell lung cancer guidelines, temozolomide was recommended for the first time as one of the available options for relapsed small cell lung cancer, and temozolomide can be chosen as a chemotherapy option for patients with sensitive or refractory relapses with a time to relapse of less than 6 months.