The main role of chemotherapy drugs in treating cancer is to stop the proliferation, infiltration and metastasis of cancer cells until they eventually kill the cancerous tissues. Most of the chemotherapeutic drugs used at present mainly use drugs to inhibit cell proliferation and tumor growth to exert their anti-cancer effects. Meanwhile, the vast majority of chemotherapeutic drugs are also toxic to normal cells, especially some bone marrow cells and epithelial cells of the digestive tract. Therefore, the goal of selecting effective drugs is to choose those that can significantly inhibit or control the growth of tumor cells with minimal toxicity to humans. In those most effective chemotherapy regimens, the drugs not only inhibit or completely remove tumor cells, but also restore the bone marrow and other organs to a normal state, or at least to a satisfactory state. Some chemotherapy drugs are taken as tablets, others are given intramuscularly or subcutaneously, there are intrathecal injections (intrathecal injections) into the spinal cord, and more commonly, they are given intravenously. Intravenous injections can be given in a few minutes or placed in a large volume of fluid and dripped over several hours. Sometimes several drugs are applied simultaneously. Chemotherapy is often given in courses, which may have intervals to allow normal cells to recover. The interval is 1 week or several weeks, depending on the type of drug or the application of the drug. The number of courses depends on the type of treatment and the purpose of the treatment (to cure or control the cancer). Chemotherapy patients undergo a physical examination, blood tests, and X-rays. It is possible to ask your doctor about the results of the tests and those that indicate the progress of your disease. Usually, people mention little about side effects. Sometimes people think that if there are no side effects, the drug is ineffective. Or if there are side effects, the drug works well. But side effects are not always the same for every patient, and their presence or absence is usually not a sign that treatment is working. So, when does a patient need chemotherapy? Chemotherapy becomes the mainstay of cancer treatment when a tumor has metastasized. It is now recognized that systemic micro-metastases also often occur in early stages of cancer, and that micro-metastases are associated with certain prognostic factors, so chemotherapy is now also used to treat early systemic lesions. Indications for chemotherapy: 1.Malignant tumors of hematopoietic system, sensitive to chemotherapy, can be completely controlled or even cured by chemotherapy, such as leukemia, multiple-issue myeloma, malignant lymphoma, etc. 2.Some solid tumors with better chemotherapy effect, choriocapillary epithelial carcinoma, malignant staphyloma, germ cell tumor, ovarian cancer, small cell lung cancer, etc. 3.Adjuvant chemotherapy after surgical resection and local radiotherapy or before surgery for solid tumors, such as breast cancer, non-small cell lung cancer, gastric cancer, colorectal cancer, etc. 4. Combined with radiotherapy for radical treatment of some tumors: head and neck tumors: nasopharyngeal cancer, laryngeal cancer, oral cancer, etc.; chest tumors: esophageal cancer, lung cancer; abdominopelvic tumors: cervical cancer, rectal cancer, anal canal cancer. 5.Solid tumors with extensive or distant metastases, not suitable for surgical resection and radiotherapy; solid tumors with recurrence or spread after surgical resection or radiotherapy, palliative chemotherapy can be considered. 6.Cancerous effusion in body cavity, including thoracic cavity, pericardial cavity and abdominal cavity, can be controlled or disappeared by intracavitary injection of chemotherapy drugs.