B-cell lymphoma, unclassifiable, with features intermediate between diffuse large B-cell lymphoma and Burkitt lymphoma

Epidemiology and Etiology:

• Infrequent
• Adults mainly

Common sites:

• Widespread often
• Extranodal often
• BM frequently
• PB frequently
• CNS frequently

Gross features:

Histologic features:

• Morphology intermediate between DLBCL and BL usually:
• cell size
• some cells smaller than typical DLBCL
• some cells larger than typical BL
• all intermediate sized cells commonly
• nuclear contours may be relatively irregular
• nucleoli may be relatively large
• relatively small nuclei with finely granular chromatin rarely (blastic or blastoid) (should be TdT negative)
• few admixed small lymphocytes typically
• no stromal reaction or fibrosis typically
• high proliferation fraction
• starry-sky pattern typically
• many mitotic figures
• prominent apoptosis
• Morphology may be typical for BL but with atypical immunophenotype and/or genetic features

Immunophenotype:

Marker:	Sensitivity:	Specificity:
MIB-1 (high)  Range 50-100%  > 90% commonly < 90% or heterogenous sometimes
BCL2	Some, if morphology resembles BL (suggests dual translocation)
sIg (typically, but double-hit cases may be negative)
TdT (neg)	Rare cases may be TdT positive, with MYC gene rearrangement +/- BCL2 rearrangement (controversial, consider lymphoblastic lymphoma diagnosis)

• Cases of morphologically typical DLBCL with a very high proliferation index should not be included
• Generally immunophenotype is suggestive of BL
• Morphology may be typical for BL with atypical immunophenotype and/or genetic features

Molecular features:

• High Grade Lymphoma Testing Guidelines
• IG genes clonally rearranged
• MYC translocations (8q24) (35-50%)
• Many involving non-IG genes
• Sole abnormality is likely BL even with atypical morphology
• Cases of otherwise typical DLBCL with MYC translocation should not be included
• Cases of otherwise typical BL without MYC translocation should not be included
• BCL2 translocation (15%)
• Sometimes together with MYC translocation (double hit)
• If not together with MYC gene rearrangement, consider DLBCL diagnosis
• BCL6 translocations
• Sometimes together with MYC and/or BCL2 (double/triple hit)
• If not together with MYC gene rearrangement, consider DLBCL diagnosis
• Complex karyotype esp with non-IGH MYC and double hit cases
• “MYC-complex” commonly (6 or more abnormalities by array CGH)

Other features:

• aggressive

References: