Precursor B lymphoblastic leukemia/lymphoma

Precursor B-cell neoplasm Precursor B-lymphoblastic leukemia/lymphoma Mature (peripheral) B-cell neoplasms B-cell chronic lymphocytic leukemia/small lymphocytic lymphoma... 

Loss of a pan-T cell antigen Abnormal CD4/CD8 only suggestive Classical Hodgkin lymphoma Expression of CD30 and CD 15 Lack of expression of CD45 B cell-antigen expression variable Precursor lymphoblastic leukemia/lymphoma TdT-positive... 

Also known as the common ALL antigen, CDIO is a zinc metallopeptidase expressed in early lymphoid progenitors and normal germinal center cells. It is almost always present on the surface of precursor B lymphoblastic and Burkitt lymphomas, and much less frequently precursor T lymphoblastic leukemia/lym-phoma. Many FLs and some diffuse large B-cell lymphomas, along with multiple myeloma, are positive. CDIO and BCL-6 are commonly considered markers of germinal center origin (Fig. 6.10). 

B- and T-cell neoplasms are divided into precursor disorders (lymphoblastic leukemias and lymphomas) with normal counterparts in the earliest bone marrow and thymus compartments, and mature, or peripheral, malignancies akin to normal extrathymic, nodal, splenic, or circulating lymphocytes. Discussion is focused on those malignancies commonly diagnosed using immunohistochemistry (i.e., solid tumors). 

Terminal deoxynucleotidyl transferase (TdT) is a DNA polymerase active during the process of immunoglobulin and T-cell receptor gene rearrangement early in a precursor B or T cell s life. Only normal early B and T lymphoblasts mark for TdT. The staining pattern is nuclear. TdT is a sensitive and specific antibody for lymphoblastic lymphoma/leukemia because only a small proportion of myeloid leukemia cases are positive (Fig. 6.13). 

CD20 and LCA may be negative in precursor B-cell lymphoblastic lymphoma/leukemia. 

Precursor B or T lymphoblastic lymphoma/leukemia has a similar overall cell size to Burkitt lymphoma but tends to have finer chromatin with inconspicuous nucleoli. These lymphomas have an immature phenotype and usually demonstrate positivity for TDT and/or CD34 with dim positivity for CD20 at best, and the absence of surface immunoglobulin allows a separation from Burkitt lymphoma. 

The terminal deoxynudeotidyl transferase (TdT) is a 58-kDa DNA nuclear polymerase, which catalyzes the template independent polymerization of deoxynucleo-tidyl triphosphates to double-stranded gene segment DNA. TdT is mainly expressed in primitive B- and T-lymphocytes. Antibodies to TdT are used as a spedfic marker for the diagnosis of precursor cell lymphomas, namely acute lymphoblastic leukemia and lymphoma. 

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