How is proliferation in ALL?

• Proliferation of typically small to medium sized cells • B and T cell precursors are morphologically indistinguishable • B-ALL / LBL – CD19, CD79a, CD22, TdT, CD34, CD10 and PAX5 • T-ALL / LBL – Typically TdT, CD34, CD99 and CD1a – CD7 and cCD3 most commonly positive – Variable expression of CD2, CD5, • T-ALL often double positive for CD4 and CD8 – Only cytoplasmic CD3 considered lineage specific for T cells • Hypercellular, starry sky, TdT +