Nodal Involvement by CD30+ Cutaneous Lymphoproliferative Disorders and Its Challenging Differentiation From Classical Hodgkin Lymphoma.

Primary cutaneous lymphomas are defined as non-Hodgkin lymphomas that present in the skin with no evidence of extracutaneous disease at the time of diagnosis. Mycosis fungoides is the most common type of primary cutaneous T-cell lymphoma, representing almost 50% of primary cutaneous T-cell lymphomas, and primary cutaneous CD30+ T-cell lymphoproliferative disorders are the second most common group (30%). Transformed mycosis fungoides is usually CD30+ and can involve multiple nodal sites; other primary cutaneous CD30+ T-cell lymphoproliferative disorders can also involve draining regional nodes. Nodal involvement by CD30+ T-cell lymphoproliferative disorders can mimic classical Hodgkin lymphoma, which can aberrantly express T-cell antigens. The aim of this article is to briefly review salient clinical, histologic, immunophenotypic, and molecular features that can be used to distinguish lymph node involvement by CD30+ cutaneous T-cell lymphomas and lymphoproliferative disorders from classical Hodgkin lymphoma, a clinically important differential diagnosis that represents a challenging task for the pathologist.