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The US Food and Drug Administration(FDA) has accepted for priority review the biologics license application seeking approval for tagraxofusp (Elzonris, SL-401) to treat blastic plasmacytoid dendritic cell neoplasm (BPDCN).

The FDA expects to make a decision on this application by February 21, 2019.

The FDA grants priority review to applications for products that may provide significant improvements in the treatment, diagnosis, or prevention of serious conditions.

The agency intends to take action on a priority review application within 6 months of receiving it rather than the standard 10 months.

About tagraxofusp

Tagraxofusp is a targeted therapy directed to CD123, a cell surface receptor expressed on a range of malignancies. The drug is being developed by Stemline Therapeutics, Inc.

In addition to priority review, tagraxofusp has breakthrough therapy designation and orphan drug designation from the FDA.

Tagraxofusp has produced favorable early results in a phase 2 trial of patients with BPDCN. Results from this trial were presented at the 23rd Congress of the European Hematology Association (EHA) in June.

Results were presented for 45 patients—32 with previously untreated BPDCN and 13 with relapsed/refractory BPDCN.

Three patients received tagraxofusp at 7 μg/kg/day on days 1 to 5 of a 21-day cycle, and the rest received the drug at 12 μg/kg on days 1 to 5 of a 21-day cycle.

Among patients who received the 12 μg/kg/day dose, the overall response rate was 83% (35/42). The overall response rate was 90% (26/29) in the previously untreated patients and 69% (9/13) in relapsed/refractory patients.

The composite complete response rate was 62% (n=26) overall, 72% (n=21) in previously untreated patients, and 38% (n=5) in relapsed/refractory patients.

Fourteen patients went on to stem cell transplant, 1 of whom had relapsed/refractory disease at baseline.

Overall survival results were only available for the 29 previously untreated patients who received tagraxofusp at 12 μg/kg/day. In this group, the median overall survival had not been reached at a median follow-up of 13.8 months (range, 0.2 to 37.4 months).

Safety results were presented for 114 patients who have received tagraxofusp at 12 μg/kg/day on all trials of the drug. These data include patients with diseases other than BPDCN, although adverse events (AEs) were similar regardless of disease.

Common treatment-related AEs (of any grade, occurring in at least 15% of patients) included hypoalbuminemia (49%), ALT increase (48%), AST increase (48%), thrombocytopenia (29%), nausea (27%), pyrexia (25%), chills (23%), fatigue (23%), weight increase (19%), hypotension (18%), peripheral edema (17%), and vomiting (15%).

Another common AE was capillary leak syndrome (CLS), which occurred in 20% of patients (n=23). Most cases of CLS were grade 1 or 2, but there were grade 3 (n=5) and 4 (n=2) cases, as well as a single case of grade 5 CLS that occurred in a BPDCN patient.

Researchers found they could manage the CLS with monitoring and protocol adjustments.

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