Follicular T‐cell lymphoma: description of a case with characteristic findings suggesting it is a different condition from AITL

Sir: T-cell lymphomas with a follicular growth pattern (FTCLs) are a rare and otherwise unspecified variant of peripheral T-cell lymphoma (PTCL-u), since their cellular origin and clinical implications are uncertain. We report a case of follicular T-cell lymphoma with a pure follicular pattern, paratrabecular bone marrow infiltration and a T follicular-helper (TFH) immunophenotype. An asymptomatic 49-year-old woman with no previous relevant clinical history was admitted to the Haematology Department of the Complejo Hospitalario de Xeral-Calde (Lugo, Spain). At the time of admission, a computed tomography scan detected multiple systemic lymphadenopathy as well as a homogeneous giant hepatosplenomegaly. b2-Microglobulin and lactate dehydrogenase levels were normal. A lymph node biopsy was performed. The patient was treated for stage IV-A lymphoma with cyclophosphamide, doxorubicin, vincristine and prednisolone. Normal lymph node architecture was effaced and replaced by a proliferation of small ⁄ medium-sized lymphoid cells with a distinct nodular growth pattern. The neoplastic lymphocytes, occupying the centre of the follicles, showed relatively monomorphous cytology. A preserved follicular dendritic cell (FDC) network was present within the follicles, without interfollicular expansion. Neither reactive blasts, plasma cells, eosinophils nor epithelioid venule hyperplasia were found in the paracortex (Figure 1). Neoplastic lymphoid cells were positive for CD3, CD4, CD5, CD43, PD1, CXCL13, CD57, Bcl-6 and Bcl-2 and negative for p53 and SYK (Figure 1). CD10 was only weakly expressed by a subset of the neoplastic T cells. B cells had disappeared from the germinal centres (GCs), which were exclusively occupied by follicular T cells. A rim of mantle zone B cells remained, encircling the neoplastic follicles. There were no cells positive for Epstein–Barr virus (EBV) encoded small nuclear RNA. It has been proposed that such cases are related to angioimmunoblastic T-cell lymphoma (AITL). Nevertheless, the case presented here had distinctive features while lacking other AITL features in its clinical presentation (absence of B symptoms, autoimmune phenomena, cutaneous rash, hypergammaglobulinaemia), morphology (absence of hyperplastic epithelioid venules, plasmacytosis, eosinophilia, polymorphic cell composition) and immunophenotype (EBV)). Previous examples of the same tumour described here, could be those reported by Macon, van der Oord, Leval, Hatano et al. and probably some of those included in the abstract by Huang et al. In contrast, cases described by Bacon and Rodriguez-Justo probably represent what has been termed early AITL, or AITL with limited nodal involvement and hyperplastic follicles (pattern I), a disorder that in some cases has been shown to progress to classic AITL. Cases classified by Rudiger as PTCL with perifollicular growth pattern, by Ikonomou as PTCL with involvement of the mantle zone, and by Uherova as PTCL mimicking marginal zone B-cell lymphoma might also be examples of early AITL, where a conspicuous rim of neoplastic TFH cells surrounds reactive GCs. This differs from the observations described here, where GCs were fully replaced by a monomorphous infiltrate of neoplastic TFH cells. We cannot rule out the possibility that all these tumours with a TFH immunophenotype correspond to different stages of the same process, as suggested by Qubaja et al. and Jiang et al.; but our personal experience and the review of the published cases leads us to believe that FTCL does not relapse as classic AITL. Alternatively, they could represent the expansion of a TFH subset lacking homing for the outer zone of the GC. 8 Interestingly, Streubel et al. described the translocation t(5,9) (q33; q22) involving the ITK ⁄ SYK genes in PTCL cases with a nodular pattern whose morphology might be equivalent to the case described here, which was, nevertheless, negative for this translocation. Bone marrow involvement by both PTCL-u and AITL is a relatively frequent phenomenon. The morphological pattern in PTCL-u is quite heterogeneous, whereas AITL usually presents with both interstitial and paratrabecular infiltrates. The case presented here consisted of a polymorphous infiltrate containing both atypical T lymphocytes and reactive B blasts,