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 patient's blasts would most likely demonstrate -

Ans. is 'b' i.e., An immature T cell phenotype o Increased leucocyte count in the range of 138 x 109/L 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.