Stemline Therapeutics, a clinical-stage biopharmaceutical company developing novel oncology therapeutics, provides an update on its ongoing pivotal phase II trial in blastic plasmacytoid dendritic cell neoplasm (BPDCN), using Stemline’s experimental compound, SL-401. BPDCN at present has no approved treatment.

On January 18, the company received a report that a patient death had occurred. The patient had developed capillary leak syndrome (CLS), a known, sometimes fatal, and well-documented side effect of SL-401. The cause of the patient’s death has not yet been determined. The safety profile for SL-401 includes CLS, and there have been previous deaths reported in patients with CLS in this trial, which have been disclosed in public presentations. That CLS is an expected complication of the administration of SL-401 has also been identified in filings with the Securities and Exchange Commission (SEC) and FDA, as well as in the study’s informed consent forms and other information provided to investigators.

As with all study events, the company has and will continue to report the data to the FDA in accordance with the study protocol and applicable regulations. Stemline plans to provide a clinical and safety update on this cohort when the cohort and data are complete. The pivotal phase II trial with SL-401 in BPDCN is currently ongoing, patient enrollment is ahead of schedule, and patients continue to receive SL-401 in the trial. Our timelines for study completion and BLA submission remain on track.

Stemline Therapeutics is a clinical stage biopharmaceutical company developing novel oncology therapeutics. Stemline is developing three clinical stage product candidates, SL-401, SL-801 and SL-701. SL-401 is a targeted therapy directed to the interleukin-3 receptor (CD123) present on a wide range of malignancies. SL-401 is being advanced through a pivotal Phase 2 program in patients with blastic plasmacytoid dendritic cell neoplasm (BPDCN), an indication for which SL-401 has been granted Breakthrough Therapy Designation (BTD) by the FDA. SL-401 has demonstrated high overall response rates (ORR), with multiple complete responses (CRs), in both first-line and relapsed/refractory patients, and treatment duration and frequency of bridge to transplant have been trending favorably.

SL-401 is also being advanced through phase I/II trials of patients with additional malignancies including acute myeloid leukemia (AML) in remission with minimal residual disease (MRD), high-risk myeloproliferative neoplasms (MPN), and relapsed/refractory multiple myeloma (in combination with pomalidomide). SL-801 is a novel oral small molecule reversible inhibitor of XPO1 that has demonstrated broad in vivo and in vitro preclinical activity in a wide array of solid and hematologic malignancies. A phase I trial with SL-801 is open and enrolling patients with advanced solid tumors, and a phase I trial in hematologic malignancies is planned. SL-701 is an immunotherapy designed to activate the immune system to attack tumors. A phase II trial with SL-701 in adult patients with second-line glioblastoma multiforme (GBM) is ongoing.