In clinical practice, rheumatologists and oncologists often use methotrexate, cyclophosphamide and other drugs, which are often called “chemotherapy drugs” by the general public. Therefore, when rheumatologists prescribe these drugs to patients, they often make them doubtful. Why do we need chemotherapy drugs to treat rheumatic diseases? What if there are side effects after using chemotherapy drugs? The above-mentioned doubts lead to poor compliance of patients and greatly reduce the effectiveness of treatment. In fact, on the balance of pros and cons, in many cases, it is necessary to use “chemotherapy drugs” for rheumatic diseases. Let’s explore the reasons for this. First of all, it is necessary to introduce the concept that rheumatic disease is a general term for a large group of diseases, including many independent diseases, such as rheumatoid arthritis, systemic lupus erythematosus, dry syndrome, systemic vasculitis, etc. Most of them are caused by problems with the immune function of the body. It is important to emphasize that the immune function problem here is not what we usually call “immune deficiency”, but rather immune dysfunction or “hyperimmune function”. Under normal circumstances, our immune system is like a guard to protect the body from germs, but when rheumatic diseases occur, these “guards” begin to become “fully armed” and “indistinguishable from the enemy “This is the cause of rheumatic diseases. Tumor is a malignant disease, and the principle of tumor treatment is “either one or the other”. The abnormal growth of a certain part of the patient’s body excessively consumes the nutrients needed to maintain the body’s daily life, thus leading to the failure of the body. For example, methotrexate is used to treat lung tumors at a dose of about 40-50mg at a time, and it is difficult to avoid adverse physical reactions with large doses. Rheumatic diseases are not malignant diseases, but chronic inflammatory diseases. The main purpose of rheumatic disease treatment is: to adjust the body’s disordered immune system and inhibit the overactive immune function. Since methotrexate, cyclophosphamide and other drugs have very good immunomodulatory effects, they are often used in the treatment of rheumatic diseases, but the dose and application methods are very different from those for tumors. The use of drugs for rheumatic diseases is highly individualized, and doctors choose to use drugs of different strengths and weaknesses depending on the type and severity of the disease, and generally speaking, the treatment is much milder than that for oncological diseases. Also for methotrexate, the dosage in the treatment of rheumatoid arthritis is usually 10mg to 15mg once a week, which is much lower than the dosage for oncology treatment. The treatment of rheumatic diseases is often a long-term process, and careful monitoring and conditioning is required during treatment. Any drug treatment has side effects, and patients often do not follow medical advice because of concerns about drug side effects. In fact, the benefits of treatment far outweigh the risks of side effects. For example, certain diseases, which survive for less than 2 years without the use of hormones and cyclophosphamide, can allow most patients to survive for a long time with their use; patients with rheumatoid arthritis generally develop joint deformities within 2 years if they do not use immunomodulators, while methotrexate can effectively prevent disability. Common side effects of the above drugs include elevated transaminases, blood in the urine, and anemia, which usually do not cause serious problems under close monitoring by doctors. The benefits of immunomodulators are more obvious compared to side effects. In addition, the choice of medication varies between rheumatic diseases depending on the type and severity of the disease. Patients with milder forms of the disease are treated relatively gently, while others require more “aggressive” treatment. Not all rheumatic diseases require the use of immunomodulators. In summary, unlike tumors, many patients with rheumatic diseases need and should be treated with methotrexate, cyclophosphamide, and other drugs. Long-term clinical practice has confirmed that drugs such as methotrexate are not only safe and effective but also economical in treating rheumatic diseases and can reduce patients’ pain, control disease progression and improve their quality of life. It is important that patients need to use the drugs in a standardized and reasonable manner under the guidance of rheumatologists.