<prompt> A17-year-old boy presented with TLC of 138x109 L with 80 blasts on the peripheral smear. Chest X-ray demonsnstrated a large mediastinal mass. Immunophenotyping of this patents blasts would most likely demonstrate:No surface antigens null phenotypeAn immature T cell phenotype TdtCD34CD7 positiveMyeloid markers, such as CD13,CD33 and Cd15B cell markers, such as CD19,CD20 and CD22  <response>: Answer is B An immature T cell phenotype-TdtCD34CD7 positive The presence of a mediastinal mass in a young adolescent male suggests the diagnosis of precursor T cell ALL. Precursor T cell ALL is phenotypically characterized by an immature T cell phenotype and is positive for TDT and CD7 and may he positive for CD34. The patient in question has a Tcell ALL Precursor T cell ALL Patient is presenting with characteristic clinical features of T cell ALL Occurance in an adolescent age group 17 year old Occurance in a male predilection for males Presence of a mediastinal mass High WBC count 100,000mm3 Presursor T cell ALL will show an immature T cell Phenotype and will be positive for CD7 and Td t Immunophenotypic classification for ALL FAB classification Immunologic classification Phenotype Incidence cases Cytogenetic Abnormalities Pre-B Cell Early Pre-B CD19, CD20-, CD10, CD34, TdT 55 75 t9;22, t4, 11, t1; 19 Pre-B CD19, CD20-, CD10, CD34-, clgM, Tdt- 20 B cell B cell CD19, CD20, CD22, CD10-, CD34-, Tdt-, slg 5 14q 11 or 7q34 T cell T cell CD1, CD2, CD3, CD5, CD7, CD10-, CD34-, Tdt, dual CD4CD8 20 t8; 14, t8; 22, t2;8 