ICOS and angioimmunoblastic T-cell lymphoma: The histology of AITL is very unique: (1) AITL tumor cells which are small to medium in size typically have abundant pale cytoplasms with round and slightly irregular nuclei; (2) AITL tumor cells show the cell-of-origin of TFH cells with expression of five TFHcell-associated genes (CD10, BCL-6, PD1, CXCL13, and ICOS) in most cases.