Composite mantle cell lymphoma with cryptic ins(11;2)(q13;p11.2p11.2)/IGK::CCND1 and lymphoplasmacytic lymphoma with MYD88 L265P mutation.

A woman in her 80 s presented with generalized lymphadenopathy, bone marrow (BM) involvement, and leukemic manifestation. Lymph node biopsy revealed typical histopathology of mantle cell lymphoma (MCL) and the CD5+ and immunoglobulin μ+δ+/λ+ immunophenotype, with unmutated IGHV. BM was infiltrated with not only MCL but also another B-cell tumor that was CD5- and μbright+δ+/κ+, being consistent with M proteins in the serum and urine, with mutated IGHV. As the latter lymphoma component carried the MYD88 L265P mutation, this case represented a composite of MCL and lymphoplasmacytic lymphoma. Next-generation sequencing revealed a cryptic insertion of IGK enhancer sequences into the CCND1-major translocation cluster, accounting for CCND1 expression in MCL cells recognized by immunohistochemistry. Composite lymphoma is rare, but a correct diagnosis is required because effective treatments for each component are now available.