Usefulness of multiparametric flow cytometry in detecting composite lymphoma: study of 17 cases in a 12-year period.

Composite lymphoma (CL) is a rare occurrence of 2 or more morphologically and immunophenotypically distinct lymphoma clones in a single anatomic site. A retrospective analysis of 1,722 solid tissue samples clinically suggestive of lymphoma was carried out in our institute during a 12-year period to evaluate the efficacy of flow cytometry (FC) in identifying CL. We report 17 CL cases. A strong correlation between morphologic findings and FC was observed in 13 cases (76%). In the 4 cases diagnosed as non-Hodgkin lymphoma plus Hodgkin lymphoma, although FC did not detect Reed-Sternberg cells, it accurately identified the neoplastic B- or T-cell component. In 3 cases, FC indicated the need to evaluate an additional neoplastic component that was not morphologically evident. Our data demonstrate that FC immunophenotyping of tissues may enhance the performance of the diagnostic morphologic evaluation of CL. To the best of our knowledge, this is the first report in the literature of a wide series of CL studied also by FC.