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Phenotyping and genotyping of composite lymphoma with Ki-1 component
1Department of Laboratories, North Shore University Hospital-Cornell University Medical College, Manhasset, New York 11030.
Insights
This study reports a rare composite lymphoma in an adult B-cell, featuring anaplastic large-cell Ki-1 lymphoma and follicular lymphoma. The findings suggest a follicular lymphoma transformation into Ki-1 lymphoma, originating from a single clone.
Area of Science:
- Hematology
- Oncology
- Immunology
Background:
- Composite lymphomas are rare, involving two distinct lymphoma types within a single lymph node.
- Anaplastic large-cell Ki-1 lymphoma is typically a T-cell malignancy seen in children, making its presence in an adult B-cell lymphoma unusual.
Observation:
- A 66-year-old woman presented with a composite lymphoma in her splenic hilar lymph node, comprising Ki-1 lymphoma and follicular lymphoma.
- Immunohistochemistry and flow cytometry revealed distinct immunophenotypes for each component, with shared monoclonal IgM-lambda expression.
Findings:
- The Ki-1 lymphoma component expressed CD20, CD74, and CDw75, while the follicular lymphoma expressed CD20 and CDw75 but lacked CD74 and CD30 (Ki-1).
- Immunogenotyping indicated a shared clonal origin, with both components likely arising from the same B-cell precursor.
- Rearrangement in the IgH switch region, without heavy chain switching, may have initiated the transformation from low-grade follicular lymphoma to high-grade Ki-1 lymphoma.
Implications:
- This case supports the hypothesis that B-cell Ki-1 lymphoma can arise from follicular lymphoma transformation.
- Understanding the molecular mechanisms driving this transformation is crucial for developing targeted therapies for composite lymphomas.
- The study highlights the importance of comprehensive immunophenotypic and genotypic analysis in diagnosing and classifying complex lymphoma cases.
Abstract:
A case of composite lymphoma consisting of an anaplastic large-cell Ki-1 lymphoma and a small-cell follicular lymphoma was found in the splenic hilar lymph node of a 66-year-old woman. The Ki-1 lymphoma showed monoclonal IgM-lambda and CD 20, CD 74, and CDw 75 antigens by immunostaining and CD 19, CD 20, CD 22, and lambda antigens by flow cytometry. The follicular lymphoma also showed monoclonal IgM-lambda, and CD 20 and CDw 75 antigens but not CD 74 and CD 30 (Ki-1) by immunostaining. Flow cytometric analysis of the follicular lymphoma component was not conclusive, as it was impossible to separate the neoplastic from the normal small B lymphocytes. Ki-1 lymphoma usually is seen in childhood and is mostly of T cell origin. It is, therefore, unusual to find Ki-1 antigen component in a composite lymphoma of B-cell origin in an adult. However, there has been evidence to suggest that B-cell Ki-1 lymphoma may be related to follicular lymphoma. Thus, our case may represent a follicular lymphoma transforming into a Ki-1 lymphoma. Immunogenotyping in this case revealed that the two components were probably of the same clonal origin, as they seemed to share the same light chain gene. The presence of rearrangement in the switch region of the IgH in our case without the actual occurrence of heavy chain switching may have triggered somatic recombination in the IgH complex. This series of events may have led to the transformation of a low-grade lymphoma into a high-grade lymphoma, accounting for the two morphologic patterns seen in our bimorphic lymphoma.
