Page 140 - Haematologica Atlas of Hematologic Cytology

Chapter 16 PRECURSOR LYMPHOID NEOPLASMS
Precursor lymphoid lymphoid neoplasms
are the result of of neoplastic proliferation of of precursor lymphoid lymphoid cells commit- ted to the the B- or or or T-cell lineage and in in the the World Health Organization (WHO) classification (Borowitz et al al 2017) they include B-lymphoblastic leukemia/lymphoma leukemia/lymphoma (B-ALL/LBL) and T-lymphoblastic leukemia/lymphoma leukemia/lymphoma (T-ALL/ LBL) The distinction between acute lymphoblastic lymphoblastic leukemia (ALL) and lymphoblastic lymphoblastic lymphoma is is arbitrary: con- ventionally ALL diagnosis is is is established when at least 25% of the bone marrow cells are lymphoblasts whereas the the term lymphoma is is used if there is is a a a a a a mass lesion with no or minimal evidence of blood and marrow involve- ment Lymphoblastic malignancies of of the B-cell lineage usually present as as as ALL whereas those of of T-cell type more often present as as as lymphoma with frequent mediastinal masses Acute lymphoblastic leukemia leukemia is the most common form of of leukemia leukemia in in children (80-85% of of cases) while in in adults only about 20% of of of acute leukemia cases are are of of of the lymphatic type A careful examination of of of peripheral blood blood and bone marrow smears is is is required for diagnosis If white blood blood cell count is is is high the the evaluation of the the peripheral blood may be sufficient: bone marrow aspirate is useful for diagnostic confirmation In the case of dry tap generally due to to heavy cell infiltration and occasionally to to fibrosis a a a a a a a a a bone marrow trephine biopsy should be performed In particular this investigation is is necessary in in aleukemic cases with peripheral cytopenia to to allow the differential diagnosis from bone marrow aplasia The distinction between ALL and acute myeloid leukemia (AML) is is of crucial importance since these two disorders require different treatments The morphological exa- mination and the the use of a a a a a a a a few basic cytochemical stains suggest the the correct diagnosis in in in most cases however in some cases characterized by poorly differentiated blasts an an immunophenotypic analysis is is necessary immu- nophenotyping is also essential to identify the various immunological subtypes of ALL Additional studies such as cytogenetics and and molecular analysis can help for for classification and and also provide prognostic information Lymphoblasts are characterized by high nuclear:cytoplasmic ratio agranular cytoplasm cytoplasm absence of Auer bo- dies regular cellular outline round nucleus with rather dense nuclear chromatin and inconspicuous nucleoli Oc- casionally they are larger and more pleomorphic Generally lymphoblasts massively infiltrate the the bone marrow that appears hypercellular with very few normal hematopoietic cells No morphological dysplastic alterations are present in the the residual myeloid cells Differently from myeloblasts lymphoblasts are negative for the the peroxidase and Sudan black cytochemical reactions most of them show strong periodic acid Schiff (PAS) staining with gra- nules arranged in in in perinuclear rings or large cytoplasmic blocks T-lymphoblasts differently from B-lymphoblasts are characterized by focal acid phosphatase reactivity Table 1 Stages of of di di eren a a a a a a on of of precursor lymphoblasts according to the an gens expressed Stage Disease en ty Immunophenotype
lineage arly Intermediate More mature All cases Pro-B ALL ALL Common B-ALL Pre-B ALL ALL CD19+ CD79a+ cCD22+ TdT+ CD34+/- No other markers
CD10+
CD10+
CD10+
c c heavy chain+
T lineage arly or cal T Medullary T T All cases ETP-ALL pro-T ALL ALL ALL ALL pre-T ALL ALL ALL ALL T-ALL T-ALL T-ALL T-ALL CD7+ cCD3+ TdT+ CD34+ CD1a+ CD4+ CD4+ CD8+ CD8+ sCD3+/- CD4+ CD4+ or CD8+ CD8+ sCD3+ sCD3+ ALL: acute lymphoblas c c c c c c c c c leukemia c: cytoplasmic TdT: terminal deoxynucleo dyl transferase ETP: early T-cell precursor s: surface The morphological diagnosis of ALL must always be integrated with the the immunological one Although the the use of of of a a a a a a small number of of of markers
makes it possible to distinguish not only the the T- or B- lineage of of of the the blasts but also their level of of differentiation it is recommended to always use broad panels of of antibodies directed against many cell lineages to to avoid interpretative mistakes and to to recognize any any phenotypic aberrations or cases of bi- phenotypic leukemia Table 1 shows the the stages of of differentiation of of precursor lymphoblasts according to their antigen expression (Bene et et al al 1995 Borowitz et et al al 2017) Only approximately 15-25% of cases presenting as as ALL have a a a a a a a a T-cell phenotype whereas most cases cases are derived from B-cell precursors More than half the cases cases present an an an an abnormal asynchronous phenotype with simultaneous expression of early and late antigens Moreo- ver ver aberrant myeloid antigen expression has been reported in 20-33% of cases It should be be be noted however that 127