Guidelines on Diagnosis and Treatment of Malignant Lymphomas

B Cell Lymphoma
Definition and Incidence
Aggressive large cell B cell lymphomas with morphologic
and genetic features of both DLBCL and Burkitt lymphoma
but with atypical features which preclude classification with
either of these entities. Some of these cases were previously
classified as Burkitt-like lymphoma. Some cases have mixed
morphology intermediate between DLBCL and BL, others
have typical morphology of BL but atypical immunophenotype
or genetic features.
This disease category is heterogenous, infrequently diagnosed,
and is not a distinct entity but allows classification of cases which
are impossible to classify as classical DLBCL or BL.
ICD – O Code: 9680/3
Clinical Presentation
Many cases present with extra-nodal disease but there is no
particular association with ileocaecal or jaw location. Bone
marrow and peripheral blood may be involved.
Pathology
There is a diffuse proliferation of medium to large sized lymphoid
cells with frequent mitotic and apoptotic activity and many
macrophages with a “starry sky” appearance.
Nuclear morphology is more variable than in classical BL
including variation in nuclear size, nuclear irregularity and/or
prominent nucleoli. In some cases morphology is typical of
BL but immunophenotype and/or genetic features are not.
Occasional cases have smaller nuclei resembling lymphoblasts.
Cases of morphologically typical DLBCL with very
high proliferation fraction should NOT be included.
Immunophenotype
B cell markers are positive, including CD20, CD19 and CD79a.
Surface Ig is typically positive. Ki67 labelling index is usually
very high. Many cases in this category demonstrate a typical
immunophenotype for BL (CD10+, BCL6+, BCL2- IRF4/MUM1-)
but atypical morphology. Cases with typical morphology of BL but
atypical immunophenotype (BCL2+) are also included although
such cases may also represent a “double-hit” phenomenon with
both BCL2 and MYC translocations.
Genetics
Clonal Ig gene rearrangements are present. 35-50% of cases have
8q24/MYC translocation but unlike BL many of these are non
IG-MYC translocations. BCL2 translocation is present in up to 15%
of cases and may be associated with MYC (“double hit”) and/or
BLC6 translocations. A complex karyotype is frequent, unlike BL.
Staging
As for Burkitt Lymphoma
Recommended investigations
As for Burkitt Lymphoma
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