<unk>  (PTFL) is a disease in which malignant B-cells (i.e. a lymphocyte subtype originating from the bone marrow) accumulate in, overcrowd, and cause the expansion of the lymphoid follicles in, and thereby enlargement of the lymph nodes in the head and neck regions and, less commonly, groin and armpit regions. The disease accounts for 1.5% to 2% of all the lymphomas that occur in the<unk>  age group. Initially, PTFL was found only in children and adolescents and termed<unk>  follicular lymphoma. More recently, however, the disease has been found to occur also in adults. This lead the World health Organization (2016) to rename the disorder<unk> . (The disease is also referred to as<unk> -type nodular follicular lymphoma.) At the same time the World Health Organization also recognized PTFL as a clinical entity distinct from the follicular lymphoma disorders in which it was previously classified. This reclassification was based on fundamental differences between the two diseases. PTFL differs from follicular lymphoma in its clinical manifestations, its pathophysiology including the genomic alterations (i.e. chromosome abnormalities and gene mutations) which occur in the diseases malignant cells, and its clinical course. Relative to the last point, PTFL often presents histologically as a high-grade malignancy but unlike the small percentage of follicular lymphoma cases that similarly present as a high grade malignancy, it almost invariably takes an indolent, relapsing and remitting course without progressing to a more aggressive and incurable form. Recognition of PTFL as a distinct disease separate from follicular lymphoma is critical to avoid mistaking it for a more aggressive lymphoma that requires potentially toxic chemotherapy treatments. This appears to be particularly the case when PTFL occurs in children, adolescents, and perhaps very young adults. A significant percentage of cases that were once diagnosed as PTFL are now regarded as being large B-cell lymphoma with IRF4 rearrangements, a very rare disease that was provisionally defined by the World Health organization (2016) as distinctly separate from PTFL. PTFL is here described based on this recently formulated and important distinction.
Pediatric-type follicular lymphoma
Nodal marginal zone B cell lymphoma
Duodenal-type follicular lymphoma
Marginal zone B-cell lymphoma
Nodular lymphocyte predominant Hodgkin lymphoma
Follicular lymphoma
Indolent lymphoma
AIDS-related lymphoma