Pediatric-type follicular lymphoma (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[1] and, less commonly, groin and armpit regions.[2] The disease accounts for 1.5% to 2% of all the lymphomas that occur in the pediatric age group.[3]

Reference
Wiki: Pediatric-type follicular lymphoma