Cutaneous manifestations of blastic plasmacytoid dendritic cell neoplasm: a retrospective study of morphological and immunophenotypic features

Background Blastic plasmacytoid dendritic cell neoplasm (BPDCN) is a rare, aggressive malignancy which is diagnostically challenging. Objectives To characterize clinical, histopathological and immunophenotypic features of BPDCN with cutaneous involvement. Materials & Methods Cases of BPDCN with skin lesions diagnosed between 2010 and 2020 were retrospectively studied. Results The age at diagnosis presented a bimodal pattern. The morphological features of skin lesions of BPDCN were heterogeneous, manifesting as disseminated, sporadic or solitary plaques, nodules or tumours. Histopathologically, tumour cells in 67.9% of lesions infiltrated in a diffuse and nodular pattern. Interstitial, lichenoid and perivascular patterns were observed in 14.3%, 7.1% and 10.7% lesions, respectively. Angioinvasion and necrosis were absent. All tumour cells were lymphoblastic-like with polymorphic and irregular nuclei except for one lesion revealing monomorphous immunoblastic-like cells. Immunohistochemically, CD4, CD56, CD123 and TCL-1 were positive in 82.1%, 92.9%, 96.0% and 100% cases of BPDCN, respectively. Simultaneous expression of the four markers were observed in 65.0% of stained lesions. Notably, E2-2 was positively expressed in the nuclei of tumour cells in all BPDCN lesions, but was negative in all myeloid sarcoma lesions. Moreover, peripheral blood flow cytometry of six BPDCN cases revealed varying degrees of tumour cells with heterogeneous expression of CD56. Conclusion The morphological and phenotypic features of cutaneous BPDCN are heterogeneous. E2-2 may serve as a useful marker to definitively diagnose BPDCN