Mext is used alone or together with other medicines to treat several types of cancer, such as breast, head and neck, lung, blood, bone, lymph node, and uterus cancers. Mext is also used to treat adults with severe rheumatoid arthritis and children with polyarticular juvenile idiopathic arthritis who had other treatments that did not work well. It is also used to control symptoms of severe psoriasis in adults who have not been helped by other treatments. Mext belongs to the group of medicines known as antineoplastics (cancer medicines). It blocks an enzyme that is needed by cells to live. This interferes with the growth of cancer cells, which are eventually destroyed by the body. For patients with arthritis or psoriasis, Mext may work by improving the immune system. Mext is available only with your doctor's prescription. Once a medicine has been approved for marketing for a certain use, experience may show that it is also useful for other medical problems. Although these uses are not included in product labeling, Mext is used in certain patients with the following medical conditions: Acute myeloid leukemia (blood and immune system cancer). Bladder cancer. Brain lymphoma (tumor). Bullous pemphigoid (immune system disease). Cancer of the penis. Crohn disease (intestine or bowel disease). Eye lymphoma (tumor). Felty syndrome (condition with rheumatoid arthritis, large spleen, and low white blood cells). Hodgkin disease (lymph system cancer). Ovarian cancer (ovaries). Soft tissue sarcoma (tumor in connective tissue). Systemic lupus erythematosus (immune disease). Urinary tract cancer (urine system).