Abnormalities of the thymus can result in a decreased number of T cells and autoimmune diseases such as autoimmune polyendocrine syndrome type 1 and myasthenia gravis. These are often associated with cancer of the tissue of the thymus, called thymoma, or tissues arising from immature lymphocytes such as T cells, called lymphoma. Removal of the thymus is called thymectomy. Although the thymus has been identified as a part of the body since the time of the Ancient Greeks, it is only since the 1960s that the function of the thymus in the immune system has become more clear.