Tagraxofusp demonstrated efficacy in a phase 2 trial of patients with previously treated or untreated blastic plasmacytoid dendritic cell neoplasm (BPDCN).
The overall response rate was 90% in previously untreated patients who received the highest dose of tagraxofusp and 67% in patients with relapsed/refractory BPDCN.
The researchers wrote that capillary leak syndrome (CLS) was an important adverse event in this trial, as it caused two deaths. However, the researchers developed strategies that appear to mitigate the risk of CLS in patients taking tagraxofusp.
The trial included 47 patients – 32 with previously untreated BPDCN and 15 with relapsed/refractory BPDCN. The patients’ median age at baseline was 70 years and 83% were men.
Three patients (all previously untreated) received tagraxofusp at 7 mcg/kg per day, and 44 patients received a 12 mcg/kg per day dose. All patients were treated on days 1-5 of a 21-day cycle.
Response and survival
In the 29 previously untreated patients who received the 12 mcg/kg dose of tagraxofusp, the overall response rate was 90%. The rate of complete response plus clinical complete response in these patients was 72%.
In the 15 patients with relapsed/refractory BPDCN, the overall response rate was 67%, and the rate of complete response plus clinical complete response was 33%.
A total of 14 patients, 13 of whom had previously untreated BPDCN, went on to transplant.
In the 29 previously untreated patients, the median overall survival was not reached at a median follow-up of 25 months. The overall survival rate was 62% at 12 months, 59% at 18 months, and 52% at 24 months.
In the 15 previously treated patients, the median overall survival was 8.5 months.
Common adverse events in this trial were ALT increase (64%), AST increase (60%), hypoalbuminemia (55%), peripheral edema (51%), thrombocytopenia (49%), nausea (45%), pyrexia (45%), and fatigue (45%).
Among the 44 patients who received the 12 mcg/kg dose of tagraxofusp, 8 (18%) developed CLS. Six patients had grade 2 CLS, one had grade 4, and one had grade 5. There was an additional CLS-related death in a patient who received tagraxofusp at 7 mcg/kg.
After the first death, the trial protocol was amended to reduce CLS risk. Inclusion criteria were changed so that patients must have normal cardiac function, adequate kidney function, and serum albumin of at least 3.2 g/dL. Additionally, the researchers began monitoring patients’ weight, albumin levels, and kidney function. The team withheld tagraxofusp if patients experienced rapid weight gain or if their serum albumin or systolic blood pressure fell too low.
The trial was sponsored by Stemline Therapeutics. The researchers reported relationships with Stemline and other companies.