Abstract： To the Editor:The most frequently reported adverse event of pemetrexed was myelosuppression.Here,we reported a patient with advanced lung adenocarcinoma showing pemetrexed-associated ischemic colitis.A 56-year-old female patient was admitted to our department due to the presence of a right lung mass and ipsilateral pleural effusion.Transbronchial biopsy and subsequent sequence analysis of the right lower bronchus showed poorly differentiated adenocarcinoma with no mutations in the epidermal growth factor receptor gene.Pleural biopsy revealed a metastatic lung adenocarcinoma,which suggested that radical treatment would not be beneficial.The patient was initially treated with six cycles of a first-line chemotherapy using pemetrexed (500 mg/m2,day 1)and carboplatin (area under the curve 5,day 1).Thereafter,partial remission was gained,and maintenance single-substance therapy with pemetrexed was given leading to stabilization of tumor growth.The patient was transferred to the emergency department as she showed severe,diffuse abdominal pain with hematochezia 3 days after administration of pemetrexed during the 17th maintenance therapy.