254
U N I T 3
Hematopoietic Function
to various lymphoid tissues throughout the body, espe-
cially the liver, spleen, and bone marrow.
The classification of NHLs remains controversial
and is still evolving. A commonly used classification
is the World Health Organization (WHO) system
4,7,41
(Chart 11-2). The WHO system classifies lymphomas
in terms of cell type (B or T cell), level of maturation
(e.g., immature or mature), and anatomic sites (e.g.,
MALT lymphoma of the stomach).
4
The NHLs are
actually a complex group of almost 40 distinct enti-
ties, based on the appearance of the lymphoma cells,
the presence of surface markers (e.g., antigens, CD
markers), and genetic features.
4,5,19
In addition, the
specific types of lymphomas are sometimes grouped
together into low-grade, aggressive, and very aggres-
sive categories.
Mature B-Cell Lymphomas.
Mature (peripheral) B-cell
lymphomas are the most common type of lymphoma in
the Western world. The most common of the mature
B-cell lymphomas are the follicular lymphomas (22%)
and diffuse large B-cell lymphomas (31%). Small lym-
phocytic lymphoma, mantle cell lymphoma, periph-
eral T-cell lymphoma, and MALT lymphoma together
account for 28% of NHLs.
4
Follicular lymphomas
are derived from germinal cen-
ter B cells and consist of a mixture of centroblasts and
centrocytes. Follicular lymphomas are a particularly
common neoplasm in the United States, where they con-
stitute about one third of all adult NHLs, with a peak
incidence at 60 years of age. The lymphoma predomi-
nantly affects lymph nodes. Other sites of involvement
include the spleen, bone marrow, peripheral blood, head
and neck region, gastrointestinal tract, and skin. Most
persons have advanced disease at presentation and an
indolent clinical course, with a median survival of 6 to
10 years.
7
Over time, approximately one of three follicu-
lar lymphomas transforms into a fast-growing diffuse
large B-cell lymphoma.
Diffuse large B-cell lymphomas
are a heterogeneous
group of aggressive germinal or postgerminal center
neoplasms. The disease occurs in all age groups but is
most prevalent between 60 and 70 years of age. The
cause of diffuse large B-cell lymphoma is unknown,
but may involve EBV or HIV infections. It is a rap-
idly evolving, multifocal, nodal and extranodal tumor.
Manifestations are typically seen at the time of presen-
tation. As a group, diffuse large B-cell lymphomas are
rapidly fatal if untreated.
42
However, with intensive
combination chemotherapy, complete remission can be
achieved in 60% to 80% of persons and approximately
40% to 50% remain disease free after several years and
can be considered cured.
7
Burkitt lymphoma,
one of the most rapidly growing
tumors of the NHLs, is also a disorder of germinal cen-
ter B cells. Endemic Burkitt lymphoma is the most com-
mon childhood cancer (peak age 3 to 7 years) in Central
Africa, often beginning in the jaw.
4
It occurs in regions of
Africa where both EBV and malarial infections are com-
mon. Virtually 100% of patients with African Burkitt
lymphoma have evidence of previous EBV infection,
and their tumors carry the EBV genome and express
EBV-encoded antigens.
4
Malarial infections in this pop-
ulation have been shown to cause T-cell immunodefi-
ciencies, and it is postulated that this association may be
the link between EBV infection and the development of
lymphoma. A sporadic or nonendemic form of Burkitt
lymphoma occurs less frequently in other parts of the
world. The classic presentation of endogenous Burkitt
lymphoma is a destructive tumor in the jaw and other
facial bones (Fig. 11-8), whereas the sporadic form typi-
cally presents with abdominal masses. Both forms of
Burkitt lymphoma respond to aggressive chemotherapy,
with a cure rate of up to 90%.
4
Mantle cell lymphomas
constitute less than 10% of
NHLs and have their origin in the naive B cell. After
the precursor stage, B cells undergo immunoglobulin
(Ig) gene rearrangements and develop into surface IgM-
and IgD-positive naive B cells. These cells give rise to
mantle cell lymphoma. Mantle cell lymphomas do not
occur in children, but affect older persons (median age,
60 years).
4,7
They have a rapid rate of progression, and
only one in five persons survives at least 5 years.
Marginal zone lymphomas
involve late-stage memory
B cells that reside in the marginal zone or outermost
compartment of the lymph node follicle. Variants of
marginal node lymphoma include splenic marginal zone
lymphoma and MALT lymphomas of the stomach and
other mucosal surfaces.
Mucosa-associated lymphoid
tissue lymphomas
constitute 5% to 10% of all B-cell
NHLs.
4
Most MALT lymphomas involve the stomach
or other mucosal sites, including the respiratory system.
Mucosa-associated lymphoid tissue lymphomas tend to
CHART 11-2
WHO Classification of Selected Non-
Hodgkin Lymphomas (most common)
B-Cell Lymphomas
Precursor B-cell lymphomas
B-cell lymphoblastic lymphoma
Mature B-cell lymphomas
Diffuse large B-cell lymphoma
Mediastinal large B-cell lymphoma
Follicular lymphoma
Small lymphocytic lymphoma
Lymphoplasmacytic lymphoma
Mantle cell lymphoma
Mucosa-associated lymphoid tissue (MALT)
lymphoma
Burkitt lymphoma
T-Cell Lymphomas
PrecursorT-cell lymphomas
T-cell lymphoblastic lymphoma
MatureT- (and natural killer) cell lymphomas
Anaplastic large cell lymphoma
PeripheralT-cell lymphoma (unspecified)
Developed from theWorld Health Organization. Available
at:
/
tokyomeeting/B_6-3%20Annex1.pdf
