Follicular lymphoma

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Follicular lymphoma, abbreviated FL, is a very common non-Hodgkin lymphoma. It is a small cell lymphoma and usually has an indolent behaviour.

Follicular lymphoma
Diagnosis in short
LM DDx diffuse B-cell lymphoma, other small cell lymphomas
IHC CD20 +ve, CD10 +ve, BCL-6 +ve, BCL-2 +ve
Gross white lesions +/-subtle fine nodularity (fish flesh-like appearance)
Site lymph node, spleen
Prevalence common
Prognosis usually good
Clin. DDx other causes of lymphadenopathy - other lymphomas, metastatic carcinoma

General

Gross

  • Lymph node enlargement.
  • Classically white and uniform - usually described as fish flesh-like.
    • May have a vague nodularity.

Images

  • FL in a lymph node. (WC)

  • FL in the spleen. (WC)

Microscopic

Features (lymph node):

  • Abundant abnormally-shaped lymphoid follicles - key feature - including some of the following:
    • Non-polarized mantle zone (normal mantle zone is usu. thicker at capsular aspect).
    • Non-polarized germinal center (normal germinal center has dark & light area).
    • Loss of tingible body macrophages.
    • Sinuses effaced (lost).

Note:

  • The intrafollicular component of the lymph node is compressed - follicles are often described as "kissing", as they nearly touch.
  • In bone marrow specimens the neoplastic cells classically have a paratrabecular arrangement,[1] i.e. the lymphoma cells are found adjacent to the bone spicules.

DDx:

Images

Grading

  • Grade 1-2: <= 22 centroblasts / HPF; where 1 HPF ~= 0.2376 mm^2 (22 mm eye piece @ 40X objective).
  • Grade 3A: >22 centroblasts / HPF; where 1 HPF ~= 0.2376 mm^2 (22 mm eye piece @ 40X objective).
  • Grade 3B: only centroblasts (within a nodular architecture).

Notes:

  • Significant interobserver variability.[2]
  • Grade 1 & Grade 2 lumped together.
  • One should evaluate 10 HPFs.
  • Only centroblasts without a nodular architecture is Diffuse large B cell lymphoma (DLBCL).

The usual cut points mentioned by people with HPFitis are:[3]

  • Grade 1: 0-5 centroblasts / HPF.
  • Grade 2: 5-15 centroblasts / HPF.
  • Grade 3: >15 centroblasts / HPF.

IHC

Features:[4]

  • CD10 +ve.
  • BCL6 +ve.

Others:

  • CD5 -ve.
    • +ve in mantle cell lymphoma.
  • CD23 -ve/+ve.
    • +ve in CLL.
  • CD43 -ve.
    • +ve in mantle cell lymphoma, marginal zone lymphoma.
  • CD11c -ve -- flow cytometry only.
  • CD21 -ve in tumour cells; highlights follicular dendritic cells.
  • BCL2 +ve[4] - like many other small cell lymphomas.
    • Usually negative in germinal centres.

Image:

A panel to work-up:

  • BCL2, BCL6, CD3, CD5, CD10, CD20, CD23, cyclin D1.

Molecular

  • t(14;18)(q32;q21)/IGH-BCL2 in 70-95% of cases.[4]
    • Should not be confused with t(14;18)(q32;q21)/IGH-MALT1 seen in MALT lymphomas.[5]

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RETROPERITONEAL MASS, RIGHT, CORE BIOPSIES:
- NON-HODGKIN B-CELL LYMPHOMA, FAVOUR FOLLICULAR LYMPHOMA.

COMMENT:
Morphology:
-Small cells: size ~ mature lymphocytes, quantity - many, angular and round.
-Large cells (intermixed with small cells): size ~1.5-2x mature lymphocyte, 
small nucleoli, moderate quantity of grey/basophilic cytoplasm, moderate 
nuclear pleomorphism.
-Architecture: no gland formation, discohesive, no follicles apparent, no sheets 
of large cells.
-Mitoses are uncommon.

Immunohistochemical stains (tumour cells):
Positive: CD45 (strong, membranous/cytoplasmic), CD20 (strong, membranous/cytoplasmic),
BCL-2 (strong, membranous/cytoplasmic), CD10 (strong, membranous), BCL-6 (moderate,
patchy, nuclear).

Negative: pankeratin, CD3, CD5, CD30, CD21 (follicular dendritic cells not apparent),
CD23 (scattered, rare).

Ki-67: highlights the large cells, primarily -- 5-35% of cells within the core.

The findings favour a follicular lymphoma, based on the cellular morphology and
immunostains; however, they are limited by the type of tissue sampling (core biopsy).
Clinical correlation is suggested.

See also

References

  1. ↑ Iancu, D.; Hao, S.; Lin, P.; Anderson, SK.; Jorgensen, JL.; McLaughlin, P.; Medeiros, LJ. (Feb 2007). "Follicular lymphoma in staging bone marrow specimens: correlation of histologic findings with the results of flow cytometry immunophenotypic analysis.". Arch Pathol Lab Med 131 (2): 282-7. doi:10.1043/1543-2165(2007)131[282:FLISBM]2.0.CO;2. PMID 17284114.
  2. ↑ Good, D. 17 August 2010.
  3. ↑ Mills, Stacey E; Carter, Darryl; Greenson, Joel K; Oberman, Harold A; Reuter, Victor E (2004). Sternberg's Diagnostic Surgical Pathology (4th ed.). Lippincott Williams & Wilkins. pp. 813. ISBN 978-0781740517.
  4. ↑ 4.0 4.1 4.2 Vitolo U, Ferreri AJ, Montoto S (June 2008). "Follicular lymphomas". Crit. Rev. Oncol. Hematol. 66 (3): 248–61. doi:10.1016/j.critrevonc.2008.01.014. PMID 18359244.
  5. ↑ Bacon CM, Du MQ, Dogan A (April 2007). "Mucosa-associated lymphoid tissue (MALT) lymphoma: a practical guide for pathologists". J. Clin. Pathol. 60 (4): 361–72. doi:10.1136/jcp.2005.031146. PMC 2001121. PMID 16950858. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2001121/.
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