Abstract
Lymphoblastic leukemia/lymphoma, a neoplasm of precursor B or T lineage lymphoid cells, usually involves the bone marrow and peripheral blood, and may involve nodal and/or extranodal sites. The diagnosis is based on morphologic assessment, immunophenotypic analysis, usually by flow cytometry, and genetic analysis, including cytogenetics and FISH analysis, as well as molecular diagnostic analysis. This review will focus on the flow cytometric immunophenotypic findings in B- and T-lymphoblastic leukemia/lymphoma, which include expressions of early B or T cell markers, low-level expressions of CD45, as well as expressions of terminal deoxynucleotidyl transferase (TdT), and, in many cases, stem/progenitor cell marker CD34.