Follicular T-cell lymphoma: a short review with brief discussion of other nodal lymphomas/lymphoproliferative disorders of T-follicular helper cell origin

Follicular peripheral T-cell lymphoma (F-PTCL) is a newly recognized provisional entity in the 2017 World Health Organization Classification revision of hematolymphoid neoplasms. It is a rare and under-recognized manifestation of peripheral T-cell lymphoma that is associated with a typically aggressive clinical course. Cases feature a predominantly follicular or perifollicular growth pattern and exhibit strong and consistent expression of T-follicular helper (TFH) markers. These cases distinctly lack histologic features commonly associated with angioimmunoblastic T-cell lymphoma, such as an associated polymorphous infiltrate, proliferation of high endothelial venules or expanded follicular dendritic meshworks. A relatively specific t(5;9)(q33;q22) rearrangement, leading to ITK-SYK fusion is seen in about 20% of cases. Herein, we summarize key features of F-PTCL and briefly review the evolving relationship to other nodal T-cell lymphomas/lymphoproliferative disorders of TFH-derivation.