Chronic Phase Of

In the chronic phase, the WBC count approximates 200,000/dL. The myelocyte is the predominating cell in both peripheral blood and marrow. Myeloblasts are rare. Basophilia and eosinophilia are common. There may be slight anemia, which is normocytic and nor-mochromic. The platelet count may be normal, decreased, or increased, but more than half of the patients have platelet counts greater than 1 million/^L;2 however, thrombotic phenomena are rare.3 The bone marrow is hypercellular, with a striking increase in granulocytic cells. Cells resembling Gaucher cells (sea-blue histiocytes) are observed in about 10% of cases.4 Megakaryocytes are smaller than normal. Reticulin, in biopsy sections, is increased. Collagen stains may show fibrosis. Of unique importance is the presence of the Ph chromosome, demonstrated in approximately 95% of all CML patients. Those patient with pheno-typic characteristics of CML but locking the ph chromosome must have marrow or blood specimens examined for the molecular abnormality, the BCR-ABL oncogene, which is present in all cases. By definition, those patients in whom the BCR-ABL oncogene cannot be found are considered to have an "atypical myeloproliferative disease" or "atypical CML."

The blast crises are divided into two general types, myeloid and lymphoid. Biphenotypic or mixed lymphoblastic-myeloblastic crises also have been observed.5 Lymphoid blast crisis occurs in 20-30% of patients. The cells often resemble those seen in acute lymphocytic leukemia and contain terminal deoxynu-cleotidyl transferase.6 (Terminal deoxynucleotidyl transferase is found mainly in poorly differentiated normal and malignant lymphoid cells of T-cell and B-cell origin and is lost as these lymphocytes differentiate and mature). Myeloid blast crisis may mimic acute myeloid leukemia. Megakaryoblastic7 and erythroblastic8 transformations and blast crises marked by basophilia also have been reported.

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