In rare cases, there may be involvement of the bone marrow. In spite of the evidence of bulky and disseminated disease, predominantly diffuse follicular lymphoma with 1p36 deletion appears to be an indolent 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.
Follicular lymphoma (FL) is a cancer that involves certain types of white blood cells known as lymphocytes. The cancer originates from the uncontrolled division of specific types of B-cells known as centrocytes and centroblasts. These cells normally occupy the follicles (nodular swirls of various types of lymphocytes) in the germinal centers of lymphoid tissues such as lymph nodes. The cancerous cells in FL typically form follicular or follicle-like structures (see adjacent Figure) in the tissues they invade. These structures are usually the dominant histological feature of this cancer.There are several synonymous and obsolete terms for FL such as CB/CC lymphoma (centroblastic and centrocytic lymphoma), nodular lymphoma, Brill-Symmers Disease, and the subtype designation, follicular large-cell lymphoma. In the US and Europe, this disease is the second most common form of non-Hodgkins lymphomas, exceeded only by diffuse large B-cell lymphoma. FL accounts for 10-20% of non-Hodgkins lymphomas with ~15,000 new cases of it being newly diagnosed each year in the US and Europe. Recent studies indicate that FL is similarly prevalent in Japan.FL is a broad and extremely complex clinical entity with a wide range of manifestations which have not yet been fully systematized. It is commonly preceded by a benign precancerous disorder in which abnormal centrocytes and/or centroblasts accumulate in lymphoid tissue. They may then circulate in the blood to cause an asymptomatic condition termed in situ lymphoid neoplasia of the follicular lymphoma type (i.e. ISFL). A small percentage of these cases progress to FL.