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 patent's blasts would most likely demonstrate:

Answer is B (An immature T cell phenotype-Tdt/CD34/CD7 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 > 100,000/mm3 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 t(9;22), t(4, 11), t(1; 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 CD4/CD8 20 t(8; 14), t(8; 22), t(2;8)