A tumour of the THYMUS GLAND. Such tumours are rare and are classified according to the variety of thymus tissue from which they develop. Epithelial thymomas grow slowly and rarely spread. If the tumour arises from LYMPHOID TISSUE, it may progress to a generalised non-Hodgkin's LYMPHOMA. Another variety is a thymic TERATOMA which is normally benign in women but malignant in men. Thymomas may affect the working of the immune system (see IMMUNITY), increasing the likelihood of infection. They are also associated with MYASTHENIA GRAVIS – an autoimmune disorder; removal of the gland may cure the disorder.