Tumours originating from the small population of B cells present in the thymus lead to primary mediastinal (thymic) large B cell lymphomas. These are a rare subtype of Non-Hodgkins lymphoma, although by the activity of genes and occasionally microscopic shape, unusually they also have the characteristics of Hodgkins lymphomas. that occur most commonly in young and middle-aged, more prominent in females. Most often, when symptoms occur it is because of compression of structures near the thymus, such as the superior vena cava or the upper respiratory tract; when lymph nodes are affected it is often in the mediastinum and neck groups. Such tumours are often detected with a biopsy that is subject to immunohistochemistry. This will show the presence of clusters of differentiation, cell surface proteins - namely CD30, with CD19, CD20 and CD22, and with the absence of CD15. Other markers may also be used to confirm the diagnosis. Treatment usually includes the typical regimens of CHOP or EPOCH or other regimens; regimens generally including cyclophosphamide, an anthracycline, prednisone, and other chemotherapeutics; and potentially also a stem cell transplant.