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1446 Part X: Malignant Myeloid Diseases Chapter 89: Chronic Myelogenous Leukemia and Related Disorders 1447

TABLE 89–1. White Blood Cell Differential Count at the megakaryocytes, T- and B-cell progenitors) but is not present in the
majority of blood B lymphocytes or in most T lymphocytes.
Approx-
54,56
Time of Diagnosis in 90 Cases of Ph Chromosome–Positive imately 70 percent of patients in the chronic phase have the classic
Chronic Myelogenous Leukemia Ph chromosome in their cells. The remaining 20 percent also have
312
Percent of Total Leukocytes a missing Y chromosome [t(Ph),−Y]; an additional C-group chromo-
(Mean Values) some, usually number 8 [t(Ph),+8]; an additional chromosome 22q−
Myeloblasts 3 but without the 9q+ [t(Ph), 22q−]; or t(Ph) plus either another stable
translocation or another minor clone. These variations have not been
Promyelocytes 4
shown to affect the duration of the chronic phase. Deletion of the Y
Myelocytes 12 chromosome occurs in approximately 10 percent of healthy men older
Metamyelocytes 7 than 60 years. 313,314
Variant Ph chromosome translocations occur in approximately
Band forms 14
5 percent of subjects with CML and involve complex rearrangements
Segmented forms 38 (three chromosomes), and every chromosome except the Y chro-
Basophils 3 mosome can be involved. 315–319 The Ph chromosome, that is, 22q−, is
present, but the gross exchange of chromosomal material involves
Eosinophils 2
a chromosome other than 9 (simple variant) or involves exchange of
Nucleated red cells 0.5 material among chromosomes 9 and 22 and a third or more chromo-
Monocytes 8 somes (complex variant; Fig. 89–8). High-resolution techniques have
indicated that 9q34-qter is transposed to 22q11 in simple and in com-
Lymphocytes 8 plex translocations. 320,321 Thus, the fusion of 9q34 with 22q11 seems to
323
In these 90 patients, the mean hematocrit was 31 mL/dL, mean total occur in the cells of most patients with CML. Complex translocations
white cell count was 160 × 10 /L, and mean platelet count was 442 × involving chromosome 3 have been notable. 322–324 In rare cases, a recip-
9
10 /L at the time of diagnosis. rocal translocation with a chromosome other than 9 to chromosome 22
9
Data from Hematology Unit, University of Rochester Medical Center. is larger than usual, and the posttranslocation shortening of the long
arms of 22 is not apparent. This circumstance has been referred to as a
masked Ph chromosome or masked translocation because the 22q− is not
evident by microscopic examination, 325,326 although t(9;22) may occur as
have been explained by a KIT mutation as an additional genetic abnor- judged by banding techniques or molecular probes. 327
mality or by dual clones in the marrow. 300,301 Macrophages that mimic Approximately 10 percent of patients have a deletion of the deriv-
Gaucher cells in appearance are sometimes seen. This finding is a result ative 9 chromosome adjacent to the chromosome breakpoint. Although
of the inability of normal cellular glucocerebrosidase activity to degrade this deletion is thought to be an important factor in resistance to drug
the increased glucocerebroside load associated with markedly increased effects with IFN therapy, it does not appear to be significant with the use
cell turnover. Macrophages also can become engorged with lipids, of imatinib. 214
302
which, when oxidized and polymerized, yield ceroid pigment. This pig- Molecular Probes In a small proportion of patients with a clinical
ment imparts a granular and bluish cast to the cells after polychrome disease analogous to CML, cytogenetic studies do not disclose a classic,
staining; such cells have been referred to as sea-blue histiocytes. 302 variant, or masked Ph chromosome. In these cases, use of a panel of
Collagen type III (reticulin fibrosis), which takes the silver impreg- restriction enzymes and Southern blot analyses with a molecular probe
nation stain, is commonly increased at the time of diagnosis in nearly for the breakpoint cluster region on chromosome 22 nearly always
half the patients, and is correlated with the proportion of megakaryo- detects rearrangement of fragments. This finding has led to the conclu-
303
cytes in the marrow. 304,305 Increased fibrosis also is correlated with larger sion that almost all cases of CML have an abnormality of the long arm of
spleen size, more severe anemia, and a higher proportion of marrow chromosome number 22 (BCR rearrangement). 328–332 Ph chromosome–
and blood blast cells. negative CML cells with BCR rearrangement can express p210 BCR-ABL1 ,
The marrows of CML patients have a mean doubling of microves- and such patients have a clinical course similar to Ph chromosome–
sel density compared to healthy controls and have more angiogenesis positive CML. 328,333–336
in marrow than other forms of leukemia. 306–308 This increased marrow The ability to identify the molecular consequences of the t(9;22),
vascularity decreases to normal after treatment. 309 that is, BCR rearrangement, mRNA transcripts of the mutant fusion
Progenitor Cell Growth Cells that form colonies of neutrophils gene, and p210 BCR-ABL1 , has resulted in diagnostic tests supplementary
332
and macrophages or eosinophils (CFUs) are increased in the marrow to cytogenetic analysis. These tests include Southern blot analysis of
and blood. The increase in CFUs in marrow is approximately 20-fold BCR rearrangement, 334–338 polymerase chain reaction (PCR) amplifica-
339
normal and in blood approximately 500-fold normal. The CFUs are of tion of the abnormal mRNA, and a less complex variation on the lat-
lighter buoyant density than those in normal marrow. More primitive ter, a hybridization protection assay. 340
100
progenitors that can initiate long-term cultures of hematopoiesis also PCR can achieve a sensitivity of one positive cell in approximately
are markedly increased. Spontaneous blood-derived granulocyte- 500,000 to one million cells. This extreme sensitivity requires special care
311
macrophage colony growth is common, although CFUs also respond to in analysis and the inclusion of negative controls. 341–344 Fusions e13a3,
growth factor stimulation. e14a3, and e19a2 are not detectable with standard PCR primers. 344A
Cytogenetics The marrow and nucleated blood cells of more A multicolor FISH method to detect the BCR-ABL1 fusion in
than 90 percent of patients with clinical and laboratory signs that fall patients with CML is a rapid and sensitive alternative to Southern
345
within the criteria for the diagnosis of CML contain the Ph chromo- blot and PCR-dependent methods. For diagnostic purposes, FISH is
some (22q−) as measured by G-banding, and virtually all patients have simple, accurate, and sensitive, and can detect the various molecular
the t(9;22)(q34;q11)(BCR-ABL1) by FISH. The Ph chromosome is pres- fusions (e.g., e13a2, e14a2, e1a2). 346–350 Interphase FISH is faster and
ent in all blood cell lineages (erythroblasts, granulocytes, monocytes, more sensitive than cytogenetics in identifying the Ph chromosome. If

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