Methotrexate disodium is widely used in the treatment of various cancers, including leukemia, lymphoma, and breast cancer, due to its ability to inhibit the growth of cancer cells. It is also employed in the management of autoimmune diseases such as rheumatoid arthritis and psoriasis, where it helps to reduce inflammation and slow disease progression. In addition, it is utilized in the treatment of ectopic pregnancies and as part of chemotherapy regimens. The drug works by interfering with the metabolism of folic acid, which is essential for cell replication, making it effective in controlling rapidly dividing cells.