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Cardiac myxoma and diffuse large B-cell lymphoma are uncommon tumors, yet four composite tumors have been reported since 2009. We are reporting on the fifth case providing detailed immunohistochemical and FISH analyses. The lymphoma was present as superficially located nests of large cells with patchy necrosis in the background of a typical atrial myxoma. It displayed features of DLBCL with non-germinal center phenotype, expressed EBER, LMP1, EBNA2 and shared the following features with the previously reported cases: B-cell lineage, high-grade cytology, high proliferation rate, EBV infection in latency type 3 with one tested case and an excellent outcome. The lymphomas arising within myxoma may follow a pathogenic pathway driven by EBV, whose transformation potential is unleashed in the cytokine-rich milieu of a myxoma, presumably accentuating age-related decline of adaptive immunity known as immune senescence. DLBCL arising within atrial myxoma grouped together with EBV+ DLBCL associated with valve prosthesis and with an atrial thrombus differs in the immunocompetent patients from primary cardiac DLBCL, not otherwise specified, in clinical presentation, pathological features and a course of the disease. Distinction between these groups may have important therapeutic consequences.

Engagement of plasma membrane receptors is followed by an assembly of a multimolecular complex of signaling molecules organized by scaffolding or adaptor proteins. PAG is a recently characterized transmembrane adaptor protein associated with lipid rafts, which is involved in the regulation of Src-kinases, monomeric Ras protein, and interactions with the cytoskeleton. The review provides up-to-date information about the protein that attracts increasing attention in current biomedical research.

Transmembrane adaptor protein PAG, also known as Csk-binding protein (Cbp), which binds and activates the cytoplasmic tyrosine kinase Csk, the major negative regulator of Src-family kinases, was found to be expressed in germinal centers of lymphoid follicles as well as in follicular, but not mantle cell lymphomas. Expression of PAG may reflect its role in regulation of proliferation and differentiation of germinal center B-cells. From the routine histopathology point of view, PAG might be a new positive marker of follicular lymphoma and a negative marker of mantle cell lymphoma.