The clinico-pathological spectrum of primary cutaneous lymphoma other than mycosis fungoides/Sezary syndrome.

The major aim of Session 1 of the 2018 European Association of Hematopathology/Society for Hematopathology Workshop was to collect examples of cutaneous lymphomas, excluding mycosis fungoides/Sezary syndrome, as defined in the current WHO classification of tumours of the haemetopoietic and lymphoid tissues. Overall 42 cases were submitted. These were considered in four main categories: primary cutaneous B cell lymphomas (12 cases), primary cutaneous T cell lymphomas/lymphoproliferations with CD8+/cytotoxic phenotype (12 cases), primary cutaneous CD30-positive lymphoproliferative disorders (15 cases) and primary cutaneous T cell lymphomas/leukaemias with CD4+ phenotype (4 cases). Using these cases as examples, we were able to present the full spectrum of cutaneous lymphoproliferations (excluding mycosis fungoides/Sezary syndrome), including examples of rare, provisional and new entities as listed in the 2017 update of the WHO classification. The findings are summarized in this report with emphasis on differential diagnostic considerations and the importance of clinico-pathological correlation for final subtyping. In presenting these findings we hope to raise awareness of this enigmatic group of neoplasms and to further our understanding of these rare disease entities.