The diagnosis of blastic plasmacytoid dendritic cell neoplasm (BPDCN) has been based on the expression status of multiple markers, including CD123. TCF4 was discovered recently to be an obligatory master regulator of plasmacytoid dendritic cells. We postulated that a tissue-based assay designed to detect dual CD123 and TCF4 expression would provide a highly reliable and practical marker for BPDCN in biopsy material. We designed, optimized, and validated a dual-color TCF4/CD123 immunohistochemistry stain for use in formalin-fixed paraffin-embedded tissue sections. The performance characteristics of the TCF4/CD123 stain were evaluated in 48 confirmed BPDCN cases. TCF4/CD123 coexpression was detected reproducibly in plasmacytoid dendritic cells. In BPDCN, the TCF4/CD123 stain showed coexpression in all (48/48; 100%) cases analyzed. Cases with concurrent samples from different anatomic sites showed comparable staining characteristics. In contrast, of 464 non-BPDCN cases comprising a wide range of hematolymphoid neoplasms and cutaneous lesions that might enter in the differential diagnosis of BPDCN, we identified dual expression of TCF4 and CD123 in only 1 case of B-lymphoblastic leukemia/lymphoma. On the basis of these findings, the TCF4/CD123 dual-color immunohistochemical stain had an analytic sensitivity of 100% and a specificity of 99.8%. Receiver operator characteristic analysis demonstrated an area under the curve of 1.000 (95% confidence interval: 0.999-1.000). In summary, the dual-color TCF4/CD123 immunohistochemistry stain provides a robust standalone and cost-effective assay for the diagnosis of BPDCN.
Departments of *Hematopathology
§Leukemia, The University of Texas MD Anderson Cancer Center, Houston, TX
†Department of Pathology, Faculty of Medicine, Chulalongkorn University, Bangkok, Thailand
Conflicts of Interest and Source of Funding: Supported in part by funds from Stemline Therapeutics Inc. (J.D.K.). The authors have disclosed that they have no significant relationships with, or financial interest in, any commercial companies pertaining to this article.
Correspondence: Joseph D. Khoury, MD, Department of Hematopathology, The University of Texas MD Anderson Cancer Center, 1515 Holcombe Boulevard, MS-072, Houston, TX 77030 (e-mail: firstname.lastname@example.org).