<prompt> A 17-year-old boy presented with TLC of 138 x 109 L with 80 blasts on the peripheral smear. Chest X-ray demosnstrated a large mediastinal mass. Immunophenotyping of this patients blasts would most likely demonstrate -No surface antigens null phenotypeAn immature T cell phenotypeMyeloid markers, such as CD13, CD33 and CD15B cell markers, such as CD 19, CD20 and CD22  <response>: Ans. is b i.e., An immature T cell phenotype o Increased leucocyte count in the range of 138 x 109L and on peripheral blood examination 80 of them constituating blast cells indicate acute leukemia. o The age group adolescent and the mediastinal mass suggests that this leukemia is in all likelihood a T cell leukemia. o As already explained, ALLs are made up of immature, precursor cells called lymphoblast, the diagnosis in this case is Precursor T cell acute lymphoblastic leukemia T cell lymphoblastic lymphoma T - ALL T - LBL. Immunophenotype of T -ALL T - LBL o The vast majority of precursor T - ALL T - LBL cases characteristically express nuclear terminal deoxynucleotidyl transferase Tdt, Cytoplasmic CD3 and CD7. The neoplastic T-blast cells are frequently CD-34 positive and express weak CD45. The precursor T cells are divided into three phenotypic subcategories :- Stage of maturation hninunophenotype Early precursor CD7, TdT, cCD3 Intermediate precursor common thymocyte CD7, TdT, cCD3, CD9, CD2, CD5, CD38, CD4 or CD8 Late stage Late thymocyte CD7, CD5, CD3, CD2, CD45, CD4 or CD8 Note :- CD with prefix c eg cCD3 refers to cytoplasmic CD; whereas CD without prefix c refers to surface CD. Immunophenotvpe of B celIALL Immunophenotypic classification of acute lymphoblastic leukemia Pre T cell ALL TdT, CD2, CD3, CD5, CD4, CD7, CD8 Early pre B TdT, DR, CD10, CD 19, CD24 Pre B cell TdT, DR, CD 10, CD 19, CD20, CD24, CIg B Cell DR, CD 19, CD20, CD24, SIg Following information have been added in fillVe of Robbins o Pre-B cells are also positive for another Pan B-cell marker, i.e. the transcription factor PAX5. 