CD5+ CD10+ lymphoplasmacytic lymphoma with cutaneous histologic transformation in a post-transplant setting.

Lymphoplasmacytic lymphoma (LPL) is a lymphoproliferative neoplasm characterized by small plasmacytic cells infiltrating the bone marrow and is typically associated with IgM paraprotein detection. In rare cases, LPL may undergo histologic transformation (HT) to a more aggressive, large B cell lymphoma, such as diffuse large B-cell lymphoma (DLBCL). HT with cutaneous involvement is exceedingly rare. Here, we report a case of cutaneous involvement by a CD5+ CD10+ large B cell lymphoma in a post-transplant setting, initially attributed to follicular lymphoma but determined to be LPL with additional molecular testing. These findings highlight a potential diagnostic pitfall that was resolved by using molecular techniques in tandem with morphological observations.