Fig.12.27 ).Auerrodsarespecificforneoplasticmyeloblastsandthusareahelpfuldiagnosticcluewhenpresent.InothersubtypesofAML,monoblasts,erythroblasts,ormegakaryoblastspredominate.
Classification. AMLs are diverse in terms of genetics, cellular lineage, and degree of maturation. The WHO classification relies on all of these features to divide AML into four categories (
Table 12.11 ): (1) AMLs associated with specific genetic aberrations, which are important because they predict outcome and they guide therapy; (2) AMLs with dysplasia, many of which arise from MDSs; (3) AMLs occurring after genotoxic chemotherapy; and (4) AMLs lacking any of the foregoing features. AMLs in the last category are subclassified based on the predominant line of differentiation that the tumor exhibits.
Immunophenotype. The expression of immunologic markers is heterogeneous in AML. Most tumors express some combination of myeloid-associated antigens, such as CD13, CD14, CD15, CD64, or CD117 (KIT). CD34, a marker of hematopoietic stem cells, is often present on myeloblasts. Such markers are helpful in distinguishing AML http://ebooksmedicine.net
Fig. 12.26 Acutemyeloidleukemia(AML).(A)Myeloblastswithdelicatenuclearchromatin,prominentnucleoli,andfineazurophiliccytoplasmicgranules.(B)and(C)showflowcytometryresultsfortheAMLshownin(A).ThetumorcellsarepositiveforthestemcellmarkerCD34andthemyeloidlineagespecificmarkersCD33andCD15(subset).(A,Courtesy of Dr. Robert
W. McKenna, Department of Pathology, University of Texas Southwestern Medical School, Dallas,Texas. BandC,Courtesy of Dr. Louis Picker, Oregon Health Science Center, Portland, Oregon.) from ALL and in identifying AMLs with only minimal differentiation.
Clinical Features. Most patients present within weeks or a few months of the onset of symptoms with complaints related to anemia, neutropenia, and thrombocytopenia, most notably fatigue, fever, and spontaneous mucosal and cutaneous bleeding. As mentioned earlier, these findings are very similar to those produced by ALL. Thrombocytopenia results in a bleeding diathesis. Cutaneous petechiae and ecchymoses, serosal hemorrhages into the linings of the body cavities and viscera, and mucosal hemorrhages into the gingivae and urinary tract are common. Procoagulants and fibrinolytic factors released by leukemic cells, especially in AML with the t(15;17), exacerbate the bleeding tendency. Infections are frequent and are often caused by opportunists such as fungi, Pseudomonas, and commensals. Signs and symptoms related to the involvement of soft tissues are usually less striking in AML than in ALL, but tumors with monocytic differentiation often infiltrate the skin (leukemia cutis) and the gingiva. Central nervous system spread occurs but also is less common than in ALL.