Primary large cell lymphoma of the mediastinum. A histologic and immunophenotypic study of 29 cases.

We studied the morphologic and immunologic features of 29 cases of primary nonlymphoblastic non-Hodgkin's lymphoma of the mediastinum. The patients ranged in age from 15 to 73 years, with a median of 32 years. The mean age for the 11 men (50 years) was significantly higher than that for the 18 women (32 years) (p less than 0.05). All had diffuse large cell lymphomas (six immunoblastic, 14 large cell not otherwise specified, six large cell noncleaved, one large cell cleaved, and two not subclassifiable). Sclerosis was prominent in 11 cases, none of them immunoblastic, and did not correlate with superior vena cava syndrome. The mean age (54 years) of patients with immunoblastic lymphomas was higher than that for patients with other subtypes (35 years) (p less than 0.02). Frozen-section immunoperoxidase staining disclosed monotypic immunoglobulin in 13 cases, with a high frequency of heavy-chain class switching (seven IgG, two IgA, four IgM). Sixteen cases were immunoglobulin negative; 14 of 15 cases expressed B-lineage antigens, and none expressed T-lineage antigens. Three of four cases showed immunoglobulin heavy- or light-chain gene rearrangement by the Southern blot technique. None showed rearrangement of the T-cell receptor beta-chain-gene constant region. There was no correlation between immunophenotype and morphologic subtype. The immunoglobulin-negative group was predominantly female (13 of 16 cases; p less than 0.02), and younger (mean age, 34 years versus 44 years; p = NS) than the immunoglobulin-positive group; however, the difference in age was not statistically significant. The actuarial 5-year survival was 57%, and there was no correlation between survival and either histologic subtype or immunophenotype. Mediastinal large cell lymphoma is a B-cell tumor, which frequently lacks immunoglobulin, may be primary in the thymus, has a predilection for young women, and can be cured with aggressive therapy.