Epidemiology
Non-Hodgkin’s lymphoma (NHL) is relatively common, with 7500 cases per year in the UK. It is slightly more common in men than women and the median age at presentation for all subtypes of NHL is over 50 years. High-grade lymphoblastic and small non-cleaved-cell lymphomas are the most common types of NHL seen in children and young adults. Low-grade lymphomas account for 37% of cases in patients between the ages of 35 and 64 years at diagnosis but for only 16% of cases in those below the age of 35.
Certain endemic geographical factors appear to influence the development of NHL in specific areas. Human T-cell lymphotrophic virus-1 (HTLV-1)-associated T-cell lymphoma/leukaemia occurs more frequently in Japan (Kyushu) and the Caribbean. Burkitt’s lymphoma is more common in Africa, particularly Nigeria and Tanzania. Follicular lymphomas are more common in North America and Europe but are rare in the Caribbean, Africa, China, Japan and the Middle East. Peripheral T-cell lymphomas are more common in Europe and China than in North America. Primary CNS lymphoma is rare, but a significantly higher incidence is seen in patients with HIV infection and immunosuppression.
Aetiology
Non-random chromosomal and molecular rearrangements are important in the pathogenesis of NHL and correlate with histology and immunophenotype. The most commonly associated finding is the t(14;18)(q32;q21) translocation (85% of follicular lymphomas, 28% of high grade tumours), which produces a juxtaposition of the BCL2 apoptotic inhibitor oncogene to the heavy-chain region of the immunoglobulin locus. The t(11;14)(q13;q32) translocation results in overexpression of BCL1 (cyclin D1/PRAD1), a cell-cycle control gene on chromosome 11q13, and is highly associated with mantle cell lymphoma. Chromosomal translocations involving 8q24 lead to c-myc deregulation and are frequently seen in high-grade small non-cleaved-cell lymphomas (Burkitt’s and non-Burkitt’s types), including those associated with HIV infection.
Several viruses have been implicated in the pathogenesis of NHL, including EBV (Burkitt’s lymphoma), HTLV-1 (adult T-cell leukaemia/lymphoma), human herpesvirus 8 (Kaposi’s sarcoma) and HCV (predisposes B-cells to malignant transformation by enhancing signal transduction on binding to the CD81).
Clinical presentation
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