Non-mediastinal grey zone lymphomas and report from the workshop.

Grey zone lymphomas represent borderline lesions between classical Hodgkin lymphoma (cHL) and other morphologically and immunophenotypically related diseases and entities like nodular lymphocyte predominant HL, T-cell rich B-cell lymphoma, ALK-negative anaplastic large cell lymphoma (ALCL), diffuse large B cell lymphoma (DLBCL) anaplastic variant and primary mediastinal LBCL. The sharp definition of morphological, immunophenotypical and molecular features of the "text-book cases" of each disease and the comparison with grey zone cases has reduced most of the latter cases. Two reports in this workshop dealt with the problematic non-mediastinal grey zone lymphomas, one with a cHL of T cell-type presenting in the skin as a ALK-negative ALCL and the other with the grey zone between cHL of B-cell type and ALK-negative ALCL.