Large cell lymphoma of the mediastinum: a B-cell tumour of probable thymic origin.

Fifteen cases of non-Hodgkin's lymphoma of the anterior mediastinum are reported. In the first group of four, fresh tissue was available and immunohistochemical studies demonstrated their B-cell origin, with monotypic immunoglobulin production in two. Only fixed tissue was available in the second group of 11 patients. All stained with antibody to leucocyte common antigen (PD7/26) and three showed monotypic immunoglobulin production. If the two groups are combined seven of the 15 tumours were clearly of B-cell origin. Classification on morphological grounds was difficult, with most tumours showing mixtures of centroblasts and large centrocytes, and the original diagnoses had included Hodgkin's disease (three), thymoma (one) and undifferentiated carcinoma (two). None of the patients had evidence of extra-thoracic disease at presentation and when this developed the organs involved were liver (one), kidney (two) and thyroid (one). Direct extension within the chest led to infiltration of chest wall, sternum, lung, superior vena cava and other structures. The site of origin, lack of nodal involvement and, in one case, presence of residual thymus around the tumour indicate an origin in thymic B-cells.