Decision tree for IHC subclassification. (A) The IHC algorithm was generated using the 40 PTCL-NOS cases that were classified by the GEP as PTCL-GATA3 and PTCL-TBX21. The 9 cases unclassifiable by GEP were not included in the training of the algorithm. (B) Comparison of the IHC and GEP-defined PTCL subtypes resulted in an accurate classification of 85% of cases, with 5% remaining unclassifiable.