Follicular lymphoma classification
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]
Overview
Classification
According to the WHO criteria, the disease is morphologically graded into:[1]
- Grade 1 (<5 centroblasts per high-power field (hpf))
- Grade 2 (6–15 centroblasts/hpf)
- Grade 3 (>15 centroblasts/hpf)
- Grade 3A (centrocytes still present)
- Grade 3B (the follicles consist almost entirely of centroblasts)
- The WHO 2008 update classifies
- Grades 1 and 2 now as low grade follicular lymphoma
- Grade 3A as high grade follicular lymphoma
- Grade 3B as Diffuse Large B Cell Lymphoma.
- Follicular lymphoma is graded according to the proportion of large cells (centroblasts). Studies suggest this histologic grading predicts clinical outcome, with more large cells behaving more aggressively and having a higher likelihood of transformation to diffuse large cell lymphoma. When any area of diffuse large-B-cell lymphoma is present in a Follicular lymphoma the disease should be reported as diffuse large B-cell lymphoma.[2]. There was no difference in survival outcomes between patients with Grade 3A and 3B FL, whereas patients with FL3 with more than 50% diffuse component have an inferior survival similar to the survival of those with diffuse large cell lymphoma. FL3B with cytogenetic abnormalities of BCL6 (at 3q27) are thought to be genetically more akin to germinal center type diffuse large B-cell lymphoma than FL1-3A, and is associated with a more aggressive clinical course.Patients with FL3B with BCL2 translocation appear to have a clinical course similar to patients with FL1-3A. Since FL3B is rare, the clinical behavior of FL3 in most studies is based mainly on FL3A cases.
- Pediatric-type FL, primary intestinal FL, other extranodal FLs and follicular lymphoma “in situ” (FLIS) are the other variants that are included under FL
- Pediatric-type follicular lymphoma: Pediatric-type FL is considered a rare variant of FL in the 2008 WHO classification and is generally characterized by lack of BCL2 rearrangement and t(14,18), which constitute the genetic hallmark of conventional FL seen in adults.22-26 Pediatric-type FL has a better prognosis than adult FL and is often cured with minimal therapy.
- Primary intestinal follicular lymphoma: FL of the gastrointestinal tract is a recently described entity, which is common in the small intestine with the vast majority of cases occurring in the duodenum. The morphology, immunophenotype, and genetic features are similar to those of nodal FL. However, most patients have clinically indolent and localized disease. Survival appears to be excellent even without treatment.
- Other extranodal follicular lymphoma: In many of the other extranodal sites, the morphology, immunophenotype, and genetic features are similar to those of nodal FL. Patients usually have localized disease and systemic relapses are rare.
- Follicular Lymphoma “in situ”: FLIS is characterized by the preservation of the lymph node architecture, with the incidental finding of focal strongly positive staining for BCL2 (restricted to germinal centers) and CD10 in the involved follicles, and the detection of t(14;18) by FISH.23,27-29 FLIS has been reported in patients with prior FL or concurrent FL (at other sites), as well as in individuals with no known history of FL.23,27,28 The occurrence of FLIS in the general population appears to be rare.
Other extranodal follicular lymphomas occur in almost any extranodal site. Patients usually have localized extranodal disease and systemic relapses are rare. Testicular follicular lymphoma are reported with increased frequency in children, but also are reported in adults.
References
- ↑ "Follicular Lymphomas". Retrieved 2008-07-26.
- ↑ National Cancer Institute. Surveillance, Epidemiology, and End Results Program 2015. http://seer.cancer.gov