CD4-Negative Variant of Cutaneous Blastic Plasmacytoid Dendritic Cell Neoplasm With a Novel PBRM1 Mutation in an 11-Year-Old Girl

Objectives: We report a rare case of CD4- cutaneous blastic plasmacytoid dendritic cell neoplasm (BPDCN) with a novel PBRM1 mutation. Methods: An 11-year-old girl presented with an enlarged mass on her left arm and underwent an incisional biopsy. Results: Histopathologic examination and immunohistochemistry studies showed a monotonous proliferation of blasts that were CD4-, CD56+, and CD123+. There was no evidence of leukemic dissemination. Next-generation sequencing detected PBRM1 and CIC gene abnormalities. We confirmed and validated a novel PBRM1 mutation by conventional polymerase chain reaction and Sanger sequencing. Conclusions: CD4- variant of BPDCN may be mistaken for myeloid sarcoma or extramedullary lymphoblastic leukemia/lymphoma because of their overlapping morphologic and immunophenotypic features; thus, a careful clinicopathologic evaluation is essential to reach the correct diagnosis. PBRM1 mutation seems to be a driver event in this case. Our study underscores the importance of alterations in chromatin remodeling in the pathogenesis of BPDCN.