Stage I
The tumor involves only the thymus gland and has not invaded the sac that surrounds the gland. This is also referred to as noninvasive thymoma.
Stage II
The tumor has spread beyond the thymus gland to invade the sac that surrounds the gland, the fat that surrounds the gland, or the lining of the lung cavity. Stages II and higher are also referred to as invasive thymoma.
Stage III
The tumor has invaded nearby organs, such as the lungs, the lining of the heart, or the large vessels next to the heart.
Stage IV
The tumor has spread deeper throughout the lining of the heart or the lining of the lungs (stage IVa), or has spread to other areas of the body through the bloodstream or lymphatic system (stage IVb).
