Table 1.

Requirements for defining BAL proposed by the 2008 WHO Classification of Tumors of Hematopoietic and Lymphoid Tissues (modified from reference 7)

Myeloid lineage	MPO (by flow cytometry, immunohistochemistry or cytochemistry) or Monocytic differentiation (at least 2 of the following: NSE, CD11c, CD14, CD64, lysozyme)
T-lymphoid lineage	Cytoplasmic CD3 (flow cytometry with antibodies to CD3 epsilon chain; immunohistochemistry using polyclonal anti-CD3 antibody may detect CD3 zeta chain, which is notT-cell specific) or Surface CD3 (rare in mixed phenotype acute leukemias)
B-lymphoid lineage (multiple antigens required)	Strong CD19 with at least 1 of the following strongly expressed: CD79a, cytoplasmic CD22, CD10 or Weak CD19 with at least 2 of the following strongly expressed: CD79a, cytoplasmic CD22, CD10