Blastic Plasmacytoid dendritic-cell neoplasm (BPDCN) is a rare and aggressive form of blood cancer that affects a type of immune cell. A recent multi-institutional clinical trial studied Tagraxofusp, a targeted biological therapy, to treat the disease. Tagraxofusp targets the CD123 protein, which is over-expressed by BPDCN tumor cells; Tagraxofusp is an interleukin-3 fused to truncated diphtheria toxin. The study’s results were positive and after they were published in the New England Journal of Medicine, the FDA approved the therapy to treat BPDCN.

Each year, hundreds of people in the United States are diagnosed with BPDCN, and the disease is usually treated with chemotherapy. If the disease responds well, patients may be eligible for stem cell therapy to further treat the disease. However, since the median age of diagnosis for BPDCN is 65, many patients aren’t able to undergo intensive chemotherapy to prepare for a stem cell transplant.

Phase 1 of the trial recruited patients with BPDCN or acute myeloid leukemia (AML). They received Tagraxofusp for five days of a 21-day cycle. Forty-seven patients were treated for BPDCN by the end of the trial; 32 hadn’t been treated before and 15 had. The primary outcome of the trial for BPDCN patients was a combination of complete responses and “clinical complete responses” among previously untreated patients.

Of the twenty-nine previously untreated patients in the trial who received Tagraxofusp, 45 percent were able to receive stem cell transplants. The trial treated patients up to the age of mid-80s and found no obvious difference in toxicity by age, unlike standard chemotherapy. For patients who didn’t respond well enough to have a stem cell transplant, many stayed on Tagraxofusp for several cycles.

The trial found that the most significant side effect of Tagraxofusp was capillary leak syndrome, which can be dangerous. To deal with this, researchers altered the inclusion criteria for patients to require that they have normal cardiac function and also established procedures to detect and treat the syndrome while patients were taking Tagraxofusp.

Nine cancer centers participated in the study and drew patients from around the world.

“We can celebrate this new drug; it’s great to have approval,” said Andrew Lane, co-first author of the paper and director of Dana-Farber’s BPDCN Center. “Still, we continue to work on improving outcomes for patients.”