Page 372 - Textbook of Pathology, 6th Edition

356 infiltrate into other tissues such as lymph nodes, liver, spleen,
skin, viscera and the central nervous system.
6. Cytokines. Presence of reactive inflammatory cells in the
Hodgkin’s disease is due to secretion of cytokines from the
Reed Sternberg cells e.g. IL-5 (growth factor for eosinophils),
IL-13 (for autocrine stimulation of RS cells) and transforming
growth factor-β (for fibrogenesis).

MYELOID NEOPLASMS

Based on the cell line of differentiation of the pluripotent
stem cell, the WHO classification (2002) recognises all
haematopoieitc neoplasms into 2 groups: myeloid and
lymphoid neoplasms. Since myeloid trilineage stem cells
further differentiate into 3 series of progenitor cells: erythroid,
granulocyte-monocyte, and megakaryocytic series, therefore
all examples of myeloid neoplasms fall into these three
categories of cell-lines. Based on this concept, the WHO
classification of myeloid neoplasms includes following 5
groups (Fig. 14.12):
SECTION II
I. Myeloproliferative diseases
II. Myelodysplastic/myeloproliferative diseases
III. Myelodysplastic syndrome (MDS)
IV. Acute myeloid leukaemia (AML)
Figure 14.11 The Philadelphia (Ph) chromosome. There is reciprocal V. Acute biphenotypic leukaemia
translocation of the part of the long arms of chromosome 22 to the long
arms of chromosome 9 written as t(9;22). Each of these groups is subclassifed into further types as
shown in Table 14.4. Important examples within each group
are discussed below.
marrow failure is not due to overcrowding by leukaemic cells
alone. Nevertheless, some normal haematopoietic stem cells MYELOPROLIFERATIVE DISEASES
do remain in the marrow which are capable of proliferating The myeloproliferative disorders are a group of neoplastic
and restoring normal haematopoiesis after effective anti- proliferation of multipotent haematopoietic stem cells.
leukaemic treatment.
Besides their common stem cell origin, these disorders are
5. Organ infiltration. The leukaemic cells proliferate closely related, occasionally leading to evolution of one entity
primarily in the bone marrow, circulate in the blood and into another during the course of the disease.

Haematology and Lymphoreticular Tissues

Figure 14.12 Maturation stages of myeloid cells and stages in development of myeloid neoplasms.