TART is the most important cause of infertility in adult male CAH patients. They are not malignant but longstanding TART can result in irreversible damage of testicular tissue and subsequently infertility. Because of the central localization of the tumours near the mediastinum testis, compression of the seminiferous tubules finally may lead to obstructive azoospermia and irreversible damage of the surrounding testicular tissue. In addition to the mechanical effects, the tumours may also have a paracrine (local hormone-mediated) effect on the surrounding tissue. Steroids produced by the tumour cells may be toxic to the Leydig cells and/or germ cells. The irreversible end stage of longstanding TART is tubular hyalinization (scarring and obliteration of the testicular tubules) with obstruction of the lumen and complete loss of germ cells and Sertoli cells (cells in the testes supporting the development of sperm). The end stage of TART thus combines characteristics of both obstructive and non-obstructive azoospermia.