disorder that may require long-term observation rather than overtreatment. Pediatric-type follicular lymphoma Pediatric-type follicular lymphoma (PTFL) was initially reported to occur in children ages 1–17 years old (median age ~13-14) but more recently has been reported to occur in adults. The disorder was recently defined by the World Health Organization (2016) as a distinct entity that occurs mostly in males and involves swollen lymph nodes in the head (including tonsils and adenoids), neck, or, rarely, axillary, or inguinal areas, or non-lymphoid tissues. Currently, however, patients who had exhibited or are exhibiting involvement of areas or tissues outside of the head, neck, armpit, or groin areas are now regarded as far more likely to have a newly and provisionally defined disease, large B-cell lymphoma with IRF4 rearrangement. The lesions in PTFL consists of infiltrates containing rapidly proliferating centrocytes and centroblasts that lack the t(14:18)(q32:q21.3) translocation but nonetheless often overexpress the BCL2 gene. These cells may show a loss of heterozygosity at 1p36 (20-50% of cases) that results in decreased expression of the TNFRSF14 gene (see Pathophysiology section) as well as mutations in the IRF8 (10-50% of cases), which contributes to the development and function of B cells, and the MAP2K1 gene (10-40% of cases), which regulates activation of the ERK cell signaling pathway. More than 2 dozen other genes have been reported to be mutated in rare cases of PTFL but in general the genetic abnormalities found in this disorder are fewer and less complex than those in other types of FL. PTFL has an indolent, relapsing and remitting course with a 5-year survival rate of >95%. Patients diagnosed with PTFL have been treated with chemotherapy, surgery, and combinations of these treatments. In general, these patients did well (100% survival with <5% of cases relapsing regardless of treatment modality). More recently, 36 patients have been treated with surgical resection alone followed by observation; all these patients survived with only one having a relapse. Thus, PTFL appears to be a highly indolent type of FL in which multiple studies have reported overall and progression-free survival rates of 100% and >90%, respectively, for >2 years and an estimated probability of 5-year event-free survival rate of ~96%. The therapeutic regimens versus follow-up observations that best treat this disorder in children, adolescents, and adults (adults may require different treatments than children and adolescents) requires further study. Primary follicular lymphoma of the testis Primary follicular lymphoma