Page 753 - Withrow and MacEwen's Small Animal Clinical Oncology, 6th Edition

CHAPTER 33 Hematopoietic Tumors 731

VetBooks.ir Pluripotent stem cell

Hematopoietic
multipotent stem cells

BFU-E CFU-GM CFU-EO BFU-MEG CFU-Mast/Baso?

CFU-E CFU-G CFU-M CFU-MEG

RBC Neutrophil Monocyte Eosinophil Basophil

Megakaryocyte

Platelets
• Fig. 33.20 A simplified scheme of hematopoiesis. BFU, Blast-forming units; CFU, colony-forming units;
E, erythroid; EO, eosinophil; GM, granulocytic-monocytic; MEG, megakaryocyte.

abnormalities have been reported in dogs with AML, chronic line, for example, erythroid, granulocytic-monocytic, or mega-
myelogenous leukemia (CML), and lymphoid leukemia. 624– karyocytic. Maturation results in the production of terminally
627 However, because karyotyping is difficult to perform in dogs differentiated blood cells (erythrocytes, granulocytes, monocytes,
because of the large number and morphologic similarity of their and platelets) that are delivered to the circulation. In some cases,
chromosomes and their resistance to banding, defining genetic as in the maturation of reticulocytes to erythrocytes, final develop-
factors in canine myeloid neoplasms has awaited application ment may occur in the spleen.
of molecular technologies and use of the canine genome map- The proliferation and differentiation of hematopoietic cells are
ping. 614,626,628–630 Certain forms of leukemia in dogs have been controlled by a group of regulatory growth factors. 635,636 Of these,
produced experimentally after irradiation. 631–633 In contrast to erythropoietin is the best characterized; it regulates erythroid
MPDs in cats, no causative viral agent has been demonstrated in proliferation and differentiation and is produced in the kidney,
dogs, although retrovirus-like budding particles were observed in where changes in oxygen tension are detected. The myeloid com-
the neoplastic cells of a dog with granulocytic leukemia. 634 partment depends on a group of factors, collectively referred to as
colony-stimulating factors (CSFs). These factors act at the level of
Pathology and Natural Behavior the committed progenitor cells, but also influence the functional
capabilities of mature cells. Some of these factors have a broad
A review of normal hematopoiesis will aid in understanding the spectrum of activity; others are more restricted in their target
various manifestations of MPDs. Hematopoiesis is the process cells and actions. CSFs are produced in vitro by a multitude of
of proliferation, differentiation, and maturation of stem cells cell types, including monocytes, macrophages, lymphocytes, and
into terminally differentiated blood cells. A simplified scheme is endothelial cells, and these cells likely play a role in the production
presented in Fig. 33.20. Pluripotent stem cells differentiate into and regulation of these factors in vivo. The gene for thrombopoi-
either lymphopoietic or hematopoietic multipotent stem cells. 635 etin also has been cloned, and it appears that this hormone alone
Under the influence of specific regulatory and microenvironmen- can induce differentiation of megakaryocytes and platelet produc-
tal factors, multipotent stem cells in bone marrow differentiate tion. 637 Recombinant forms of many of these growth factors are
into progenitor cells committed to a specific hematopoietic cell increasingly available.