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.