Tag Archives: FL

Lymph Node, WHO Classification

In Situ Follicular Neoplasia (ISFN)

In Situ Follicular Neoplasia (ISFN), which has been previously referred to as Follicular Lymphoma Is Situ (FLIS) is found in approximately 2% of otherwise reactive lymph nodes.  ISFN is defined as partial to total colonization of germinal centers by B-cells containing the t(14;18) BCL-2/IgH translocation characteristic of follicular lymphoma.

ISFN found as an incidental finding have a risk of developing follicular lymphoma (FL) of <= 5%.  The amount of involvement of ISFN within a lymph node does not appear to be directly related to the risk of future FL.

If patients have other evidence of lymphadenopathy, then additional biopsies may be helpful to exclude a B-cell lymphoma at another site.

Morphology

H&E staining demonstrates normal appearing lymph node architecture with well-formed and well-demarcated germinal centers.  Follicles with ISFN at first glance do not look significantly different from the adjacent reactive follicles.  Some areas of ISFN may more prominent and closely associated centrocytes (subtle).

Immunohistochemistry

  • CD10 – Strong expression
  • Bcl-6 – Positive
  • Bcl-2 – Positive (often stronger expression than surrounding lymphocytes)
  • Ki-67 – Usually significantly lower expression than that of adjacent reactive germinal centers
  • CD20 – Positive

Photomicrographs

H&E section containing ISFN. Morphologically the node appears consistent with an otherwise reactive lymph node.
H&E section of ISFN.
CD3 expression in ISFN.
CD20 expression in a follicle containing ISFN.
CD10 expression in ISFN.
Bcl-6 expression in ISFN. Note the crowding of centrocytes highlighted by the Bcl-6 positive cells.
Strong Bcl-2 expression in the ISFN. Note the brighter expression compared to the surrounding T-cells and mantle zone. An adjacent reactive follicle is negative for Bcl-2.
Low Ki-67 expression in ISFN (left side of image) compared to the high proportion of cell expression in the reactive follicle on the right.

Differentiating from partial involvement by follicular lymphoma

Sometimes it can be difficult to differentiate partial involvement of a lymph node by FL from ISFN.  The following features are helpful to differentiate partial involvement by FL from ISFN:

  • ISFN – Intact nodal architecture 
  • Partial involvement by FL – Altered architecture on H&E sections
  • ISFN – Normal sized follicles
  • Partial involvement by FL – Often enlarged follicles
  • ISFN – Sharp border between the follicle center and the surrounding mantle zone
  • Partial involvement by FL – Interface between the follicle center and mantle zone is often fuzzy or blurred.
  • ISFN – Bcl-2 is strongly positive (usually brighter than the surrounding T-cells and mantle zones); CD10 strongly positive
  • Partial involvement by FL – variable Bcl-2 and CD10 expression
  • ISFN – Atypical cells are confined to the follicle center
  • Partial involvement by FL – atypical cells (CD10/bcl2+) can be found outside of the follicle center areas

References

Swerdlow SH, Campo E, Harris, NL, Jaffe ES, Pileri SA, Stein H, Thiele J (Eds); WHO Classification of Tumours of Haematopoietic and Lymphoid Tissues (Revised 4th edition). IARC: Lyon 2017

Organ Systems, Bone Marrow, Lymph Node, WHO Classification

Follicular Lymphoma

Follicular Lymphoma (FL) is a mature B-cell lymphoma, which recapitulates or resembles germinal center B-cells.  Most cases (~85%) harbor the characteristic t(14;18), which juxtaposes the BCL-2 gene on chromosome 18 with the IgH gene on chromosome 14 (and hence BCL-2 IHC protein expression).  Most patients (~80-85) will present with advanced disease (stage III/IV), and bone marrow involvement is found in ~40% of cases with characteristic paratrabecular aggregates (mantle cell lymphoma and lymphoplasmacytic lymphoma may also have paratrabecular lymphoid aggregates).  Most of the cases that lack the t(14;18) IgH/BCL-2 translocation (and are BCL-2 negative) are typically grade 3 FLs with a BCL-6 translocation (~10-15%).  BCL-6 translocations can be evaluated for by FISH analysis, but the finding is NOT specific for FL.
 
Over time 30-50% of cases transform to diffuse large B-cell lymphoma (DLBCL).  In a small subset of transformations, a second “hit” with a MYC translocation will occur resulting in a very aggressive high grade large B-cell lymphoma: the so-called “double hit” lymphoma. 
Morphology
FL usually has at least a component of nodularity (+/- diffuse areas).  There are two cell types that make up FL, centrocytes and centroblasts.  Centrocytes are small cleaved cells with folded irregular nuclei.  Centorblasts are large cells with more open chromatin, multiple nucleoli, and more cytoplasm compared to centrocytes.  
 
Sometimes FL can have patterns that resemble marginal zone lymphoma, and can even have plasmacytic differentiation.  Therefore, it is important that a panel of markers be used to identify (or exclude) evidence of germinal center differentiation.  Occasional cases can have Hodgkin-like cells.
Immunophenotype 
Marker
Comment
Negative
Positive
Positive
Positive
  • Grade 1 – ~90%
  • Grade 2 – ~70%
  • Grade 3 – ~60%
Positive (~90%), negative cases do not contain the t(14;18), which is more common in grade 3 cases
  • Grade 1 – >90% + for BCL-2
  • Grade 2 – >80% + for BCL-2
  • Grade 3 – 50-70% + BCL-2
Positive, (~88%)
CD35
Highlights the follicular dendritic meshwork associated with FL.
Usually negative, higher grade lesions may be positive
Variable, shows low expression in low-grade processes, in distinct contrast to the high proliferation index and polarity associated with reactive germinal centers.
Negative
 
  
FL is typically expresses CD19, CD20, CD10, Bcl-6, and BCL-2 (~90%).  CD5 is not expressed in FL.  
  • Normal reactive germinal centers do not express Bcl-2.  In 90% of cases of FL, bcl-2 is expressed, which serves as a diagnostic tissue marker in lymphoma sections.
  • CD23 expression by flow cytometry has been associated with lower grade FLs (e.g. grade 1 & 2) and better survival.
Grading
  • Grade 1 & 2:  <= 15 centroblasts/HPF (based on 0.159 mm² HPF)
  • Grade 3:  > 15 centroblasts/HPF (based on 0.159 mm² HPF)
    • 3A:  Centrocytes present in the background
    • 3B:  NO centrocytes present in the background (not associated with the IgH/BCL-2 rearrangement, and usually lacks expression of CD10 and BCL-2; often MUM-1+)
Grade 1 & 2 behave in a similar fashion as a low grade lymphoma.  Grade 3 FL behaves as an intermediate grade lymphoma.  Grading of FL with counting of large cells must take into consideration the field diameter of the microscope being used.  The counts above are based on a F.N. 18 (0.159 mm² @ 40X).  Most convention pathology scopes today are F.N. 22 (0.247 mm² @ 40X), and adjustments are necessary.
Pattern
  • Predominately follicular:  >75% follicular/nodular architecture
  • Follicular and diffuse:  25-75% Diffuse areas or follicular/nodular architecture
  • Preominately diffuse:  <25% follicular/nodular areas (diffuse areas of otherwise grade 3 FL, then that component should be described as a separate component of diffuse large B-cell lymphoma)
Special Subtypes 
  • Large B-Cell Lymphoma with IRF4 Rearrangement
  • Pediatric Follicular Lymphoma
    • Occurs in children and young adults with an excellent prognosis, marked male predilection
    • The morphology is high-grade (FL grade 3) appearing
      • BCL-2 negative, lacK t(14;18)
      • CD10 + (usually)
      • MUM-1 negative
    • Associated with TNFRSF14 deletions of mutations
    • Localized process, usually in the head and neck area
  • Duodenal Follicular Lymphoma
    • Localized lesion
    • Grade 1-2 pattern
    • CD10/BCL-2 +
    • t(14;18) present
    • Lacks follicular dendritic meshwork
    • Ki-67, low expression
    • Excellent prognosis
  • Predominately Diffuse Follicular Lymphoma with 1p36 deletion
    • Localized mass (often inguinal)
    • Diffuse pattern, grade 1/2 
    • Excellent prognosis
    • Immunophenotype:  CD20+, CD10+, BCL-2+, BCL-6+, CD23+ (subset of cases)
    • t(14;18) NOT present
    • 1p36 deletion (not specific)
    • Lacks Bcl-2 rearrangement
  • Primary Cutaneous Follicular Lymphoma 
  • In Situ Follicular Neoplasm (ISFN)
References
Robbins and Cotran Pathologic Basis of Disease.  V Kumar, et al. 9th Edition. Elsevier Saunders. 2015. pp. 594-595.
 
Fedoriw Y, Dogan A. The Expanding Spectrum of Follicular Lymphoma. Surg Pathol Clin. 2016;9: 29–40. doi:10.1016/j.path.2015.11.001
 
Swerdlow SH, Campo E, Pileri SA, Harris NL, Stein H, Siebert R, et al. The 2016 revision of the World Health Organization classification of lymphoid neoplasms. Blood. 2016;127: 2375–2390. doi:10.1182/blood-2016-01-643569
 
Xerri L, Dirnhofer S, Quintanilla-Martinez L, Sander B, Chan JKC, Campo E, et al. The heterogeneity of follicular lymphomas: from early development to transformation. Virchows Arch. 2016;468: 127–139. doi:10.1007/s00428-015-1864-y
 
MD DY-PW, BacSc F. A case of t (14; 18)-negative follicular lymphoma with atypical immunophenotype: usefulness of immunoarchitecture of Ki67, CD79a and follicular dendritic cell …. … Malaysian journal of …. 2014.
 
Boyd SD, Natkunam Y, Allen JR, Warnke RA. Selective immunophenotyping for diagnosis of B-cell neoplasms: immunohistochemistry and flow cytometry strategies and results. Appl Immunohistochem Mol Morphol. 2013;21: 116–131. doi:10.1097/PAI.0b013e31825d550a
 
Cook JR. Nodal and leukemic small B-cell neoplasms. Mod Pathol. 2013;26 Suppl 1: S15–28. doi:10.1038/modpathol.2012.180
 
Olteanu H, Fenske TS, Harrington AM, Szabo A, He P, Kroft SH. CD23 Expression in Follicular Lymphoma: Clinicopathologic Correlations. Am J Clin Pathol. 2011;135: 46–53. doi:10.1309/AJCP27YWLIQRAJPW
 
Gradowski JF, Jaffe ES, Warnke RA, Pittaluga S, Surti U, Gole LA, et al. Follicular lymphomas with plasmacytic differentiation include two subtypes. Mod Pathol. 2010;23: 71–79. doi:10.1038/modpathol.2009.146
 
Katzenberger T, Kalla J, Leich E, Stöcklein H, Hartmann E, Barnickel S, et al. A distinctive subtype of t(14;18)-negative nodal follicular non-Hodgkin lymphoma characterized by a predominantly diffuse growth pattern and deletions in the chromosomal region 1p36. Blood. 2009;113: 1053–1061. doi:10.1182/blood-2008-07-168682
 
Bayerl MG, Bentley G, Bellan C, Leoncini L, Ehmann WC, Palutke M. Lacunar and reed-sternberg-like cells in follicular lymphomas are clonally related to the centrocytic and centroblastic cells as demonstrated by laser capture microdissection. Am J Clin Pathol. 2004;122: 858–864. doi:10.1309/PMR8-6PHK-K4J3-RUH3