Non-Hodgkin’s lymphoma

Published on 03/04/2015 by admin

Filed under Hematology, Oncology and Palliative Medicine

Last modified 03/04/2015

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Non-Hodgkin’s lymphoma

Malignant solid tumours of lymphoid tissue which are not Hodgkin’s lymphoma are termed non-Hodgkin’s lymphomas (NHL). This group of lymphomas is even more heterogeneous than Hodgkin’s lymphoma. The disease is the most common haematological malignancy and is currently the fifth most common cancer in the Western world. It appears to be increasing in incidence. NHL may occur at any age but the median age of presentation is 55–60 years.

Aetiology

The cause of the majority of cases of NHL is obscure. However, specific chromosomal translocations are closely associated with particular histological types. Thus, the majority of Burkitt’s lymphoma cases demonstrate the t(8;14) abnormality in which the MYC oncogene on chromosome 8 is moved next to the immunoglobulin heavy chain region on chromosome 14. Almost 90% of follicular low-grade lymphomas are characterised by t(14;18) where the BCL2 gene on chromosome 18 is moved to the immunoglobulin heavy chain region. This leads to excessive expression of BCL2, an oncogene known to inhibit apoptosis (programmed cell death). It is likely that such chromosome rearrangements require further events – perhaps co-expression of a second proto-oncogene or antigenic stimulus – to produce the clonal malignant cell. Possible triggering antigens include Helicobacter pylori in gastric MALT lymphoma and hepatitis C in marginal zone lymphoma. The aggressive extranodal lymphomas seen in AIDS are likely to result from a combination of immunosuppression (due to the HIV virus), deregulation of a proto-oncogene (MYC) and secondary viral infection (Epstein–Barr virus). Similar tumours may follow organ transplantation.

Classification

This is complex and ever-changing with a real risk of ‘heart-sink’ for the uninitiated. In simplest terms NHL can be divided into ‘high-grade’ and ‘low-grade’ types. High-grade tumours are composed of large poorly differentiated lymphoid cells. They have an aggressive clinical course but are often curable. Low-grade tumours are composed of smaller, better differentiated cells. They are more indolent clinically but have a tendency to repeatedly relapse.

The current WHO classification avoids the overly simplistic high-grade/low-grade split and divides lymphomas into more specific subtypes based on clinical features, morphology, immunophenotype, karyotype and molecular characteristics. In addition to NHL and Hodgkin’s lymphoma the WHO scheme contains a number of other lymphoid neoplasms occurring mainly at extranodal sites that are discussed elsewhere (e.g. myeloma, hairy cell leukaemia). Some of the major entities are shown in Table 30.1.

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