The decrease of white blood cells during chemotherapy is caused by the bone marrow suppression caused by chemotherapy drugs. In addition to killing the tumor cells in the body, chemotherapy drugs also kill the normal cells in the body, especially the cells that renew quickly in the body, such as the hair growth cells in the scalp, the oral cavity, the mucous membrane of the gastrointestinal tract, and the bone marrow hematopoietic cells. Therefore, chemotherapy is likely to cause hair loss, oral ulcers, gastrointestinal mucosal damage, and also bone marrow suppression. In the bone marrow suppression, it is often mainly the white blood cells that drop more, especially the neutrophils among the white blood cells, which drop most significantly. In contrast, platelets and hemoglobin generally do not decline, or may decline mildly.