Cancer of the thymus affects the small organ that rests in the front of the chest, in back of the sternum, according to the American Cancer Society. The thymus is in the chest cavity between the lungs where the heart, esophagus and parts of the windpipe and aorta are located.
Both thymomas and thymic carcinomas emerge from thymus epithelial cells, which provide the shape and structure to the organ. As of 2015, most doctors think that all thymomas have the potential to be cancerous, and the ideal way to tell if they are likely to recur after treatment is to look for spreading into surrounding tissues, notes the American Cancer Society.
The spread of thymus cancer is the primary factor in its staging. Six different staging levels describe the development of thymus cancers in the World Health Organization's classification. Type A is the least frequent type, featuring oval- or spindle-shaped epithelial cells that look normal, offering the most hopeful prognosis. As staging progresses, the cells look less like normal epithelial cells. In Type C, the most dangerous stage, cells look distorted, and the tumors have spread into distant organs and tissues and invaded nearby tissues, reports the American Cancer Society.