Diffuse Large B Cell Lymphoma

Variant: ALK Positive Large B Cell Lymphoma

Amongst lymphomas, ALK is nearly restricted to primary systemic large cell lymphoma (T lineage)
A rare set of large B cell lymphomas express ALK
- Large cells with immunoblastic features
  - Round nuclei with single large nucleolus
  - Binucleate cells common
  - One case reported with mixture of large and small cells
  - Basophilic cytoplasm, frequently with paranuclear hof
  - Frequently sinusoidal
- B lineage based on immunoglobulin expression
  - IgA 5/7 cases
  - Light chain restriction 6/7
    - Based on stains or in situ hybridization
  - B lineage markers negative (CD20, CD79a)
  - ALK membrane positive, cytoplasm +/-
    - Rare cases with clathrin-ALK t(2;17) reported
    - t(2;5) not identified
  - EMA positive 7/7
  - CD30 negative 0/7
  - CD45RB weak to moderate positive
  - T lineage negative (CD3, CD43, CD45RO)
  - CD68 negative
  - CD57 positive 5/7
- Aggressive course in 6/7 reported cases
- Note that these are distinct from anaplastic variant of large B cell lymphoma, which is ALK negative