The distinction between T3 and T4 tumours is critical because it separates conventional surgical and nonsurgical management [17]. T4 tumours may be readily identified by virtue of their invasion of a vertebral body (fig. 16), obvious invasion of the mediastinum or heart (fig. 17) or the presence of lung parenchymal metastases. T3 tumours can however be more difficult to grade principally because of the difficulties of distinguishing simple extension of the tumour into the mediastinal pleura or pericardium (T3) from actual invasion (T4).