Lymphomas

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The lymph nodes are a major site for metastasis of tumour by lymphatic spread. This is most
commonly seen with carcinomas and melanomas, occurring less frequently with sarcomas.
Clinically, development of enlarged lymph nodes may be the presenting sign of the tumour,
the diagnosis being made only after histological examination of a lymph node biopsy.
Tumour cells are first seen in the subcapsular sinus; they later form solid areas, replacing
the nodal structure. With time, tumour extends outside the nodal capsule, tethering
nodes to adjacent structures.
Typically, nodes involved by metastatic tumour are very hard and, in advanced
cases, are fixed to other structures.

HODGKIN'S DISEASE

The malignant lymphomas are primary neoplastic diseases of lymphoid cells, which have been
divided into two main groups on the basis of clinical and pathological features.
Hodgkin's disease is characterized by neoplastic proliferation of an atypical
form of lymphoid cell eponymously termed the 'Reed-Sternberg cell'.
This is the most common type of lymphoma.
Non-Hodgkin's lymphomas are characterized by neoplastic proliferation of B-lymphocytes,
T-lymphocytes or, rarely, histiocytic cells.
Hodgkin's disease involves proliferation of an atypical form of lymphoid cell that,
until recently, was extremely difficult to categorize - the Reed-Sternberg cell.
Clinically disease presents as enlargement of a single lymph node or group of nodes,
or enlarged nodes may be discovered following investigation for non-specific systemic
symptoms such as weight loss, fever, or pruritus.
Affected nodes are enlarged and replaced by firm, rubbery, pinkish white tissue
The natural history of untreated disease is spread to adjacent
lymph node groups, with involvement of spleen, liver, and bone marrow.

These lymph nodes are enlarged and replaced by firm, creamy white tissue. Although
this example was taken from a case of Hodgkin's disease, nodes in non-Hodgkin's
lymphomas may appear identical.

Prognosis in Hodgkin’s disease is related to stage and sub-type
Histologically, four main types of Hodgkin's disease have been defined
(Rye classification), each with a different natural history and prognosis.
Common to all types of Hodgkin's disease is the presence of Reed-Sternberg cells,
the morphology of which varies in different sub-types of disease. The difference between
the types is in the extent and vigour of the host immune response associated with
neoplastic transformation.
The response is marked in lymphocyte-predominant disease, moderate in mixed cellularity,
variable in nodular sclerosis, and in lymphocyte-depleted it is virtually non-existent.
The degree of associated immune response is related to prognosis, the best outcome being
seen in lymphocyte-predominant and the worst in lymphocyte-depleted disease.

Lymphocyte-predominant disease is mainly seen in young adult males.
Histologically the nodes are replaced by reactive lymphoid cells, among which are
a small population of Reed-Sternberg cells of the lymphocytic/histiocytic type. Most patients
present with Stage I or II disease.

Mixed cellularity disease mainly affects adults in later life, but any
age can be affected. Lymph nodes are replaced by an infiltrate of Reed-Sternberg cells of
the classic and mononuclear types, with a cellular response composed of lymphoid cells,
eosinophils, plasma cells and histiocytes.
Over 50% of patients present in Stage III or IV.

Lymphocyte-depleted disease is mainly seen in elderly adults. The infiltrate
is composed of many pleomorphic Reed-Sternberg cells, and shows few reactive lymphoid cells.
Most patients with this pattern present with Stage III or IV disease; it is associated
with the poorest prognosis.
Nodular sclerosis is the most common type of Hodgkin's disease, mainly affecting
young adults. In most cases the mediastinal nodes are involved at presentation.
The key feature is that the infiltrate is divided into nodules by broad bands of collagen.
In nodular sclerosis Type I the infiltrate is cytologically the same as in mixed
cellularity disease. In nodular sclerosis Type II the infiltrate contains pleomorphic
Reed-Sternberg cells and there is lymphocyte depletion.

NON-HODGKIN'S LYMPHOMAS

Non-Hodgkin's lymphomas may be classified as nodal (tumours originating in
lymph nodes, which account for the vast majority of cases) or extranodal
(tumours originating in specialized groups of lymphoid cells). Most extranodal
lymphomas arise in specialized epithelial-associated lymphoid cells
(mucosa-associated lymphoid tissue - MALT), and cases are seen in the gut and lung.
Other examples develop in tissues that have been the seat of chronic lymphocytic
inflammation in organs not normally noted to have a lymphoid population
(e.g. testis and thyroid). Lymphomas may also develop in the brain and skin as a primary disease.
Non-Hodgkin's lymphomas can be derived from either B- or T-lymphocytes.
They are composed of a predominant cell type, which can be identified
with one of the stages of differentiation of normal T- or B-cells.
On the basis of their cytology, phenotype and clinical behaviour, non-Hodgkin's lymphomas have been divided into four main groups:
1 Low-grade B-cell lymphomas (50% of cases).
2 High-grade B-cell lymphomas (30% of cases).
3 Low-grade T-cell lymphomas (10% of cases).
4 High-grade T-cell lymphomas (10% of cases).

In older classifications, histiocytic lymphomas were included.
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