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Low grade lymphoma

(This is another final part of the Sabah lymphoma talk: Part One, Two, Three.)

I. Marginal zone B cell lymphoma

  • Types: Nodal, extranodal, splenic.
  • Immunohistochemically different from mantle cell lymphoma, follicular lymphoma, and small lymphocytic lymphoma.
  • Differential diagnosis: Reactive monocytoid B-cell hyperplasia.
  • Patterns:
    • Diffuse pattern: diffuse sheets of neoplastic cells with effacement of nodal architecture.
    • Nodular pattern: distinct nodules, well-demarcated.
    • Interfollicular pattern: neoplastic cells in interfollicular areas that surround residual germinal centres.
    • Perifollicular pattern: annular distribution of neoplastic cells around the uninvolved normal secondary follicles.
  • Histology:
    • Vague nodules with sclerosed blood vessels.
    • Stromal sclerosis which compartmentalize the small groups of neoplastic cells.
    • Monocytoid / plasmacytoid cells, singly distributed or in clusters.
    • Increased large cells with nuclear pleomorphism (not seen in mantle cell lymphoma)
  • Immunohistochemistry:
    • CD20 and CD43 positive.
    • Weakly positive CD23.
    • Negative for CD5.
    • Follicular dendritic cells are distrupted with presence of interfollicular nests.
    • Low Ki-67.
II. Follicular lymphoma
  • Composed of centrocytes and centroblasts.
  • Must have at least a focal follicular pattern.
  • Follicles are crowded; may have presence of mantle zone with lack of polarization.
  • Germinal centre type with positivity for BCL-2 (85%)/
  • May have interfollicular CD10-positive cells.
  • Immunohistochemistry: Positive for CD10, BCL-6 and BCL-2
    • BCL-2 is positive in all low-grade lymphomas.
  • Variants:
    1. Paediatric
    2. Primary intestinal
    3. Extranodal
    4. Follicular lymphoma in situ (interfollicular)
  • Follicular lymphoma post Rituximab treatment:
    • CD20 negative, CD79a positive.
    • Must use more than one antibody marker.
III. Mantle cell lymphoma
  • Usually small or medium-sized.
  • Slightly irregular or cleaved nuclei.
  • Spectrum: lymphocyte-like, large cleaved, or lymphoblast-like.
  • Centroblasts and immunoblasts are rare.
  • CD5 and Cyclin D1 positive
  • Diagnostic pitfall: mantle cell lymphoma with features of marginal zone lymphoma.
IV. Small lymphocytic lymphoma (SLL)
  • Diffuse or vague nodular patter (due to proliferation center)
  • May have plasmacytoid differentiation.
  • 10% of cases may have Richter's transformation.
  • Immunohistochemistry: weak CD20 positivity, positive for CD5, CD3 and CD43.  Negative for BCL-6 and Cyclin D1.
V. Lymphoplasmacytic lymphoma
  • Also known as immunocytoma.
  • Diffuse infiltrate of LP cells and plasma cells with intrasinusoidal pattern.
  • Now considered as marginal zone lymphoma (immunohistochemistry is the same as marginal zone lymphoma)
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