Interferon regulatory factor 8 expression and features in blastic plasmacytoid dendritic cell neoplasm and extranodal NK/T-cell lymphoma, nasal type.

[AIMS] To investigate the diagnostic value of Interferon regulatory factor 8 (IRF8) in blastic plasmacytoid dendritic cell neoplasm (BPDCN) and extranodal NK/T-cell lymphoma, nasal type (ENKTL).

[METHODS] Immunohistochemistry staining was used to detect IRF8 expression in 19 cases of BPDCN and 59 cases of ENKTL. In addition, 21 cases of myeloid sarcoma, 30 of B-lymphoblastic leukemia/lymphoma (B-ALL/LBL), 30 of T-lymphoblastic leukemia/lymphoma (T-ALL/LBL), 10 of histiocytic sarcoma, 10 of Langerhans cell histiocytosis, and 9 of follicular dendritic cell sarcoma were also included. DNA sequencing detected IRF8 genetic variation in 6 cases of BPDCN and 20 cases of ENKTL.

[RESULTS] IRF8 expression was detected in 100.00% (19/19) of BPDCN, exhibiting a strong and uniform staining pattern, and in 91.53% (54/59) of ENKTL, with varying degrees of staining intensity. Weak and focal staining was detected in 33.33% (7/21) of myeloid sarcoma, 13.33% (4/30) of B-ALL/LBL, and 11.11% (1/9) of follicular dendritic cell sarcoma. No expression was found in T-ALL/LBL, histiocytic sarcoma, or Langerhans cell histiocytosis. The proportion of IRF8 positive expression was higher in BPDCN and ENKTL than in other hematolymphoid neoplasms. In ENKTL, the average IRF8 expression was higher in nasal cases than in extranasal cases and in cases with mitosis figures of more than 4/10 high-power field (HPF). Predominantly large transformed cell morphology and extranasal involvement site might serve as independent prognostic factors of two-year survival in ENKTL. IRF8 genetic point mutations were found in 33.33% (2/6) of BPDCN and 10.00% (2/20) of ENKTL.

[CONCLUSION] The study demonstrated the promising value of IRF8 in the diagnosis of BPDCN and ENKTL.