Some tumors that form in the mediastinum may be benign (noncancerous), meaning they do not grow into surrounding areas or spread in the body. Some tumors may be malignant (cancerous) tumors and may grow into nearby tissues or spread to other parts of the body (metastasize). Left untreated, even benign growths may cause serious complications as they crowd or invade the heart or its lining, major blood vessels, or the spinal cord.

A biopsy is usually recommended to determine the diagnosis of a tumor that appears suspicious on imaging. However, sometimes surgical removal without a preliminary biopsy is appropriate for mediastinal tumors.

How does mediastinal cancer develop?
In general, cancer develops after the genetic material in cells changes abnormally and the cells begin growing out of control. When there are enough of these abnormal cells, they can form a tumor.

Mediastinal masses may result from lymphomas, thymomas or thymic carcinomas, thyroid enlargement, or from benign conditions such as a thymic cyst. Thymic cysts may be aggressive and invade surrounding structures.