Follicular lymphoma pathophysiology
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Sowminya Arikapudi, M.B,B.S. [2]
Overview
Genes involved in the pathogenesis of follicular lymphoma include BCL-2 and BCL-6. The most common cause is reciprocal translocation t(14;18)(q32;q21). The progression to follicular lymphoma involves microRNAs (miRNAs). On microscopic histopathological analysis, centrocytes, centroblasts along with various non-neoplastic cells including T cells, follicular dendritic cells, and macrophages are the characteristic findings of follicular lymphoma.
Pathophysiology
Physiology
- Follicular helper T cells (Tfh) are specialized helper T-cells that are predominantly located in germinal centers along with B-cells.[1][2]
- Follicular lymphoma is the second most common non-Hodgkin lymphoma.[3].
- The disease is characterized by the clonal proliferation of neoplastic lymphoid cells that share morphological, immunophenotypic and molecular genetic attributes of germinal center B-cells.
- The development of follicular lymphoma tumors in adults is dependent upon the overexpression of B-cell leukemia/lymphoma 2 (BCL-2) located on chromosome band 18q21.
- BCL-2 is an oncogene that blocks programmed cell death (apoptosis). As such, overexpression results in prolonged cell survival.
- These tumors contain a mixture of neoplastic centrocytes and centroblasts along with various non-neoplastic cells including T-cells, follicular dendritic cells, and macrophages.
- Follicular lymphoma can be designated as low grade (1 and 2) or higher grade (3A and 3B) disease, depending on the number of centroblasts per high-power field.
Pathogenesis
- The most common cause is reciprocal translocation between (14;18)(q32;q21) in 80-85% of cases.[4]
- This somatic rearrangement is initiated within the bone marrow during B-cell lymphopoiesis and results from immunoglobulin heavy chain gene (IGH) rearrangement.
- The t(14;18) translocation leads to placement of the B cell lymphoma 2 (BCL2) gene under the influence of transcriptional enhancers associated with IGH, resulting in overexpression of anti-apoptotic BCL2 leading to increased cell survival and uncontrolled cell proliferation in germinal centers.[5][6][7]
- BCL2, along with other anti-apoptotic proteins, inhibits apoptosis by binding and neutralizing activated pro-apoptotic proteins including the mitochondrial outer membrane permeabilizers BAX and BAK, as well as the intracellular stress sensors which activate BAX and BAK.
- Mutations in chromatin-modifying genes occur, affecting histone methyltransferases, histone acetyltransferases or histone linker proteins.
- These mutations act to promote increased proliferation of B cells.
- Genes encoding components of vacuolar H+-ATPase, or RRAGC, a guanine nucleotide binding protein, regulate the mTOR activation.
- Mutations in these genes upregulate mTOR (mammalian target of rapamycin) signaling in FL cells. These mutations are found in approximately 15 to 20 percent of cases.
- Upregulated mTOR directs many cellular processes including growth, differentiation, survival, and adhesion or cellular migration, and resulting in follicular lymphoma development.
- KMT2D, CREBBP, EZH2, EP300, HIST1H1E, KMT2C, ARID1A, and SMARCA4 are some of the other genomes which undergo mutations in very few cases.
- The tumor microenvironment comprised of T cells and dendritic cells may influence the development and progression of Follicular lymphoma.
- Communication between the tumor cells and the microenvironment involves chemokines, chemokine receptors, and adhesion molecules, the balance of which determines whether there is tumor cell growth promotion or inhibition.
- MicroRNA expression- short non-coding RNAs named microRNAs (miRNAs) have important functions in follicular lymphoma biology.[8]
- In malignant B cells, miRNAs participate in pathways fundamental to B cell development like:
- B cell receptor (BCR) signaling
- B cell migration/adhesion, cell-cell interactions in immune complexes.
- The production and class-switching of immunoglobulins.[9]
- miRNAs influence B cell maturation, generation of pre marginal zone, follicular, B1, plasma and memory B cells.[9]
- It is positive for the B-cell markers CD10, CD19, CD22, and usually CD20.[10]
Genetics
- A translocation between chromosome 14 and 18 results in the overexpression of the BCL-2 gene.[11][12]
- The BCL-2 gene is normally found on chromosome 18, and the translocation moves the gene near to the site of the immunoglobulin heavy chain enhancer element on chromosome 14.
- Translocations of BCL6 at 3q27 can also be involved.[13]
Gross Pathology
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Classic appearance of spleen involved by follicular lymphoma, namely the presence of discrete, miliary, small, white "pearly" nodules throughout the whole parenchyma.
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Follicular lymphoma replacing a lymph node.
Microscopic Pathology
The tumor is composed of follicles containing a mixture of the following[14]:
- Centrocytes (small cleaved cells without nucleoli)
- Centroblasts (larger noncleaved cells with moderate cytoplasm, open chromatin, and multiple nucleoli)
- These follicles are surrounded by non-malignant cells, mostly T-cells.
Within the follicles, centrocytes typically predominate; centroblasts are usually scarce.
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Micrograph of a follicular lymphoma, showing the characteristically abnormal lymphoid follicles. H&E stain
Grading
According to the WHO criteria, the disease is morphologically graded into:[15]
- 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 provided the following grading for follicular lymphoma:
- 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
References
- ↑ Lossos IS, Gascoyne RD (2011). "Transformation of follicular lymphoma". Best Pract Res Clin Haematol. 24 (2): 147–63. doi:10.1016/j.beha.2011.02.006. PMC 3112479. PMID 21658615.
- ↑ Ochando J, Braza MS (2017). "T follicular helper cells: a potential therapeutic target in follicular lymphoma". Oncotarget. 8 (67): 112116–112131. doi:10.18632/oncotarget.22788. PMC 5762384. PMID 29340116.
- ↑ Kridel R, Sehn LH, Gascoyne RD (2012). "Pathogenesis of follicular lymphoma". J Clin Invest. 122 (10): 3424–31. doi:10.1172/JCI63186. PMC 3461914. PMID 23023713.
- ↑ Ganapathi KA, Pittaluga S, Odejide OO, Freedman AS, Jaffe ES (2014). "Early lymphoid lesions: conceptual, diagnostic and clinical challenges". Haematologica. 99 (9): 1421–32. doi:10.3324/haematol.2014.107938. PMC 4562530. PMID 25176983.
- ↑ Biagi JJ, Seymour JF (2002). "Insights into the molecular pathogenesis of follicular lymphoma arising from analysis of geographic variation". Blood. 99 (12): 4265–75. PMID 12036852.
- ↑ "A clinical evaluation of the International Lymphoma Study Group classification of non-Hodgkin's lymphoma. The Non-Hodgkin's Lymphoma Classification Project". Blood. 89 (11): 3909–18. 1997. PMID 9166827.
- ↑ Lorsbach RB, Shay-Seymore D, Moore J, Banks PM, Hasserjian RP, Sandlund JT; et al. (2002). "Clinicopathologic analysis of follicular lymphoma occurring in children". Blood. 99 (6): 1959–64. PMID 11877266.
- ↑ Fernández de Larrea C, Martínez-Pozo A, Mercadal S, García A, Gutierrez-García G, Valera A; et al. (2011). "Initial features and outcome of cutaneous and non-cutaneous primary extranodal follicular lymphoma". Br J Haematol. 153 (3): 334–40. doi:10.1111/j.1365-2141.2011.08596.x. PMID 21375524.
- ↑ 9.0 9.1 Musilova, K; Mraz, M (2014). "MicroRNAs in B cell lymphomas: How a complex biology gets more complex". Leukemia. doi:10.1038/leu.2014.351. PMID 25541152.
- ↑ Overview at UMDNJ
- ↑ Bosga-Bouwer AG, van Imhoff GW, Boonstra R; et al. (February 2003). "Follicular lymphoma grade 3B includes 3 cytogenetically defined subgroups with primary t(14;18), 3q27, or other translocations: t(14;18) and 3q27 are mutually exclusive". Blood. 101 (3): 1149–54. doi:10.1182/blood.V101.3.1149. PMID 12529293.
- ↑ Winberg CD, Nathwani BN, Bearman RM, Rappaport H (1981). "Follicular (nodular) lymphoma during the first two decades of life: a clinicopathologic study of 12 patients". Cancer. 48 (10): 2223–35. PMID 7028244.
- ↑ Bosga-Bouwer AG, Haralambieva E, Booman M; et al. (November 2005). "BCL6 alternative translocation breakpoint cluster region associated with follicular lymphoma grade 3B". Genes Chromosomes Cancer. 44 (3): 301–4. doi:10.1002/gcc.20246. PMID 16075463.
- ↑ Anderson T, Chabner BA, Young RC, Berard CW, Garvin AJ, Simon RM; et al. (1982). "Malignant lymphoma. 1. The histology and staging of 473 patients at the National Cancer Institute". Cancer. 50 (12): 2699–707. PMID 7139563.
- ↑ "Follicular Lymphomas". Retrieved 2008-07-26.