Diagnosis of Acute Leukemia
,
, 1 INTRODUCTION
Acute myeloid leukemia is characterized by the malignant transformation of myeloid stem cells
in the bone marrow, which are incapable of normal differentiation and maturation, resulting in
‘blast’ cells. Since normal hemopoiesis is organized hierarchically, the malignant
transformation can occur at several levels and AML may arise in a stem cell capable of
differentiating into cells of erythroid, granulocytic, monocytic and megakaryocytic lineages, or
in a lineage-restricted stem cell.
Rarely the transformation may occur in a stem cell capable of differentiating into both lymphoid
and myeloid lineages and a hybrid or phenotypic leukemia, where the leukemic cell may
demonstrate both lymphoid and myeloid surface markers, could result.
The FAB divides AML into nine distinct subtypes that differ morphologically and
immunologically; cytogenetic differences are also incorporated in some subtypes. The most
common subtypes are M2 and M4, followed by M1, and then by M5 and M4Eo; M3, M6 and
M7 are relatively rare. In the subtype M1, two kinds of blast account for over 90% of the
‘nonerythroid’ cells: type I blasts lack granules and type II contain granules. In the subtype M2
the blasts account for 30–90% of ‘non-erythroid’ cells and there is evidence of maturation to
the next stage or beyond; Auer rods are common. Subtype M3 cells are heavily granulated
promyelocytes, often with bundles of Auer rods in a variant type, called M3v, cells are hypo
granular. Disseminated intravascular coagulation (DIC), a condition characterized by an
inappropriate activation of the coagulation system resulting in clotting and bleeding, is
common at presentation in both varieties of M3.
Subtype M4 is characterized by myelomonocytic morphology and a monocytosis is common a
variant of M4, M4Eo is recognized when more than 5% eosinophils are seen. Two variants of
subtype M5 are recognized: M5a, in which more than 80% of the ‘nonerythroid’ cells are
monoblasts and M5b, in which less than 80% of the ‘nonerythroid’ cells are monoblasts.
Infiltration of tissues, in particular gums, perianal area and skin with blasts is frequent in
subtypes M4 and M5. In the subtypes M6 and M7, the malignant transformation occurs at the
level of the stem cells committed to the erythroid and megakaryocytic lineages.
There are two types of acute leukemia
1. Acute lymphocytic leukemia (ALL).
2. Acute myelogenous leukemia (AML).
3
,
, 1 INTRODUCTION
Acute myeloid leukemia is characterized by the malignant transformation of myeloid stem cells
in the bone marrow, which are incapable of normal differentiation and maturation, resulting in
‘blast’ cells. Since normal hemopoiesis is organized hierarchically, the malignant
transformation can occur at several levels and AML may arise in a stem cell capable of
differentiating into cells of erythroid, granulocytic, monocytic and megakaryocytic lineages, or
in a lineage-restricted stem cell.
Rarely the transformation may occur in a stem cell capable of differentiating into both lymphoid
and myeloid lineages and a hybrid or phenotypic leukemia, where the leukemic cell may
demonstrate both lymphoid and myeloid surface markers, could result.
The FAB divides AML into nine distinct subtypes that differ morphologically and
immunologically; cytogenetic differences are also incorporated in some subtypes. The most
common subtypes are M2 and M4, followed by M1, and then by M5 and M4Eo; M3, M6 and
M7 are relatively rare. In the subtype M1, two kinds of blast account for over 90% of the
‘nonerythroid’ cells: type I blasts lack granules and type II contain granules. In the subtype M2
the blasts account for 30–90% of ‘non-erythroid’ cells and there is evidence of maturation to
the next stage or beyond; Auer rods are common. Subtype M3 cells are heavily granulated
promyelocytes, often with bundles of Auer rods in a variant type, called M3v, cells are hypo
granular. Disseminated intravascular coagulation (DIC), a condition characterized by an
inappropriate activation of the coagulation system resulting in clotting and bleeding, is
common at presentation in both varieties of M3.
Subtype M4 is characterized by myelomonocytic morphology and a monocytosis is common a
variant of M4, M4Eo is recognized when more than 5% eosinophils are seen. Two variants of
subtype M5 are recognized: M5a, in which more than 80% of the ‘nonerythroid’ cells are
monoblasts and M5b, in which less than 80% of the ‘nonerythroid’ cells are monoblasts.
Infiltration of tissues, in particular gums, perianal area and skin with blasts is frequent in
subtypes M4 and M5. In the subtypes M6 and M7, the malignant transformation occurs at the
level of the stem cells committed to the erythroid and megakaryocytic lineages.
There are two types of acute leukemia
1. Acute lymphocytic leukemia (ALL).
2. Acute myelogenous leukemia (AML).
3
