Patients with lung cancer can have blood in stool, and the reasons for this are as follows: 1. caused by tumor, the lesion of tumor invades the liver and other abdominal organs, liver function is further damaged, and eventually complications such as upper gastrointestinal bleeding occur. The most common clinical manifestation of upper gastrointestinal bleeding is blood in stool, some patients further develop hypersplenism and platelet drop, platelet drop to a certain degree will lead to gastrointestinal bleeding, which will also manifest as blood in stool. 2. The main side effect of targeted drugs is bleeding. Some patients have hemorrhoids, anal fissures and other comorbidities, and in the process of chemotherapy for tumor treatment, they have difficulty in defecation to aggravate the comorbidities, which eventually also manifests as blood in stool. 3.