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A 68-year-old man presented with cervical swelling. Imaging revealed extensive supradiaphragmatic lymphadenopathy. Lymph node biopsy confirmed mantle cell lymphoma (MCL), and fluorescence in situ hybridization (FISH) confirmed IGH::CCND1 rearrangement. The patient received 6 cycles of bendamustine-rituximab and achieved complete remission with undetectable minimal residual disease by ClonoSeq. Four months later, positron emission tomography–computed tomography identified a new [¹⁸F]fluorodeoxyglucose-avid left axillary mass. Excisional biopsy showed effacement of nodal architecture by a polymorphous infiltrate containing scattered Reed-Sternberg and Hodgkin cells (hematoxylin and eosin stain). These cells expressed CD30, CD15, PAX5 (weak), MUM1, and cyclin D1 (weak, red arrow shows Hodgkin/Reed-Sternberg [HRS] cells and blue arrow shows a histiocyte), whereas negative for ALK, BCL6, CD20, and EBER-ISH (Epstein-Barr virus encoded RNA in situ hybridization). The background was rich in T cells with a mixed CD4/CD8 phenotype, expression of CD2, CD5, and CD7. Follicular dendritic cell meshwork was absent by CD21/CD23. Findings were diagnostic of classic Hodgkin lymphoma (CHL). Images were taken with 40× objective; ×800 total magnification. Despite the absence of MCL morphologic or immunophenotypic features, FISH confirmed persistence of the IGH::CCND1 rearrangement within HRS cells (white arrow). Next-generation sequencing showed no pathogenic variants, and ClonoSeq remained negative. The patient received Adriamycin (doxorubicin), bleomycin, vinblastine, and dacarbazine with complete remission.

This case illustrates, for the first time, that CHL cells can harbor the hallmark IGH::CCND1 rearrangement of preceding MCL, providing evidence of a clonal relationship between 2 lymphomas.

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