Patients with blastic plasmacytoid dendritic cell neoplasm (BPDCN) have poor outcomes despite intensive chemotherapy, underscoring the need for novel therapeutic approaches. The expression status of PD1/PD-L1 in BPDCN remains unknown. We evaluated PD1/PD-L1 by immunohistochemistry and RNAseq expression profiling in a cohort of BPDCN patients. The study group included 28 patients with a median age of 66.8 years (range, 22.8–86.7), 22 men and 6 women. PD-L1 expression was detected by immunohistochemistry in 10/21 (47.6%) cases. PD-L1 expression had a median H-score of 157. The H-score was ≥60 in 7 patients. PD-L1 protein levels (H-score) were proportional to normalized PD-L1 mRNA transcript levels (CD274 mRNA). In addition, high-level PD-L1 expression correlated with higher numbers of PD1-positive cells within BPDCN tumors. There was no correlation between clinicopathologic characteristics and PD-L1 expression status. Similarly, there was no significant difference in overall survival between patients with PD-L1-positive and PD-L1-negative BPDCN (median 12 vs. 23 month, respectively; p = 0.743). In conclusion, PD-L1 expression by tumor cells is detectable in a sizeable subset of patients with BPDCN, suggesting that exploration of the effectiveness of therapeutic inhibition of the PD1/PD-L1 axis in patients with refractory or progressive BPDCN is warranted.

T‐cell prolymphocytic leukemia (T‐PLL) is a rare, mature T‐cell leukemia which usually presents with aggressive behavior. We report an asymptomatic T‐PLL patient diagnosed by clinical features, lymphocyte morphology, and flow cytometry. Incidentally, she was found to have lymphocytosis and lymphadenopathy. Flow cytometry from blood revealed an abnormally increased CD4+ T‐cell population. T‐cell receptor clonality assessment by next‐generation sequencing revealed a dominant clone in the ß‐chain constant region. No pathogenic mutations in 25 lymphoma‐related genes were found. Due to her asymptomatic T‐PLL disease, we observed her clinical situation and blood count every three months for at least one year.

Key Clinical Message: An overlap between human herpesvirus 8 (HHV8) ‐positive diffuse large B‐cell lymphoma and HHV8‐positive germinotropic lymphoproliferative disorder has been proposed. We present a unique Epstein‐Barr virus‐associated case in which features of both conditions were present.