**3. Morphologic diagnosis**

The bone marrow aspiration test is fundamental to confirm the presence of lymphoblasts (by morphology and/or cytochemistry with special stains that include a negative MPO in 100% of cells, Periodic Acid-Shiff (PAS) (+) in 70–80%, and acid phosphatase (+) in the case of T lymphoblast). The WHO suggests greater than 20% as diagnosis criteria (if the percentage is lower, one must search for extramedullary disease at the nodal level to differentiate from the diagnosis of lymphoblastic lymphoma). The bone marrow aspiration is hypercellular 95–100% of the time; however, in those cases where the aspirate is "dry" (packed bone marrow), which corresponds to 1–2% of the cases, a bone biopsy must be carried out for histopathological confirmation. Based on morphology, the French-American-British (FAB) classification identifies three types of ALL [7, 8, 12].

The first step to integrate the diagnosis of ALL is the morphological identification of lymphoblasts. For this, it is necessary to perform a bone marrow aspirate and be observed directly under a microscope by an expert in hematology, which can be supported in other tests like special stains, as in the case of myeloperoxidase, which must be negative in all the malignant cells observed; PAS staining, which is considered

**139**

*Overview and Current News in Acute Lymphoblastic Leukemia*

positive for ALL when observed in 70–80% of cells with malignant morphology and acid phosphatase, which is used for T-cell differentiation. Regarding manual cell counting, it is necessary that the presence of 20% or more cells with malignant characteristics, as indicated by the criteria of the WHO classification, in case this criterion is not met, can be replaced by others such as the documentation of extramedullary disease. It is important to specify that most of the times, we may have difficulties in trying to obtain the sample for the bone marrow aspirate, since the large number of cells within the medullary space condition the presence of the phenomenon of "dry" aspiration; in these cases, we must carry out bone biopsy in a mandatory manner.

The French-American-British (FAB) classification that was used commonly

• L1—around 25–30% of adult cases and 85% of childhood cases of ALL are of

• L2—around 70% of adult cases and 14% of childhood cases are of this type.

• L3—this is a rarer subtype with only 1–2% cases. In this type, the cells are large and uniform with vacuoles (bubble-like features) in the cytoplasm overlying

In an initial effort, the French-American-British (FAB) was given the task of subclassifying this type of leukemia according to various morphological characteristics in order to try to determine the behavior and prognosis of each type based on its morphology; this is how the FAB morphological classification was born, which subdivides

• L1: this subtype is characterized by presenting cells with a regular nucleus, homogeneous chromatin, small or absent nucleoli, and scarce cytoplasm. It represents the majority of the ALL in children observed in up to 85%, while in

• L2: unlike the previous one, this subclassification is seen mostly in adults (70%) and its morphology is opposite to L1: chromatin is heterogeneous, the

adults, it is seen between 30% and 70% of the times.

nucleus irregular, and with multiple nucleoli.

this subtype. In this type, small cells are seen with:

The cells are large and/or have varied shapes with:

*DOI: http://dx.doi.org/10.5772/intechopen.86662*

**3.1 Images ALL**

earlier includes:

○ regular nuclear shape

○ homogeneous chromatin

○ small or absent nucleolus

○ irregular nuclear shape

○ heterogeneous chromatin

○ scanty cytoplasm

○ large nucleolus

the nucleus.

the ALL into three types:

*Overview and Current News in Acute Lymphoblastic Leukemia DOI: http://dx.doi.org/10.5772/intechopen.86662*

positive for ALL when observed in 70–80% of cells with malignant morphology and acid phosphatase, which is used for T-cell differentiation. Regarding manual cell counting, it is necessary that the presence of 20% or more cells with malignant characteristics, as indicated by the criteria of the WHO classification, in case this criterion is not met, can be replaced by others such as the documentation of extramedullary disease. It is important to specify that most of the times, we may have difficulties in trying to obtain the sample for the bone marrow aspirate, since the large number of cells within the medullary space condition the presence of the phenomenon of "dry" aspiration; in these cases, we must carry out bone biopsy in a mandatory manner.
