A case of primary cutaneous B‐cell lymphoma with immature features in an old man. Diffuse large B‐cell lymphoma with immature features or B‐cell lymphoblastic lymphoma?

Primary cutaneous B‐cell lymphomas are a heterogeneous group of lymphoid neoplasms primarily occurring in the skin. Although most cases are represented by primary cutaneous follicle center cell lymphoma, primary cutaneous marginal zone lymphoma and leg‐type diffuse large B‐cell lymphoma, other diffuse large B‐cell lymphomas and B‐cell lymphoblastic lymphoma may rarely present primarily in the skin. In this setting, the presence of histopathologic and immunohistochemical features of cellular immaturity is exceedingly rare and may represent a diagnostic challenge. We present the first case of a primary cutaneous diffuse large B‐cell lymphoma characterized by diminished expression of CD45, expression of TdT and rearrangement of MYC gene. The differential diagnosis mainly included B‐cell lymphoblastic lymphoma, and required the genetic analysis of heavy chain (IGH) gene rearrangements.