Composite lymphomas (CLs) are characterized by the rare occurrence of two or more morphologically and/or immunophenotypically different lymphomas in the same anatomic tissue site. Many different combinations of lymphoma have been reported including multiple B-cell lymphomas, B-cell and T-cell non Hodgkin lymphomas, non Hodgkin lymphomas and Hodgkin lymphoma and complex B-cell, T-cell and Hodgkin lymphoma cases. The two lymphoma components usually are not clonally related but the use of thorough molecular techniques revealed that in some cases the two components are clonally related suggesting origin from a common progenitor cell. Pathogenesis of these lymphomas remains not well defined and the etiology differs according to the types of lymphomas involved. Composite B-cell lymphomas with two distinct low grade components are rare and usually are characterized by the existence of two different unrelated progenitors. CLs consisting of two types of non Hodgkin lymphomas of the same lineage, mostly B-cells, represent in most of the cases tumor progression and transformation from an indolent B-cell lymphoma to diffuse large B-cell lymphoma (DLBCL) and the low grade and high grade components in this type of CL are often clonally related while a clonal link has also been reported in cases of CLs containing Hodgkin lymphoma with various non Hodgkin lymphomas. CLs must be carefully diagnosed because the containing disease entities may not only have different natural course but also may differ in prognosis and treatment.
Keywords: Composite lymphomas, clonality, anatomical site, morphology, molecular techniques, Non Hodgkin Lymphoma, Hodgkin lymphoma.