Stemline Therapeutics Provides Update on Clinical Programs

Stemline Therapeutics, Inc. (Nasdaq:STML), a clinical-stage biopharmaceutical company developing novel therapeutics for oncology indications of unmet medical need, today provided an update on its clinical programs.

SL-401

• Patient enrollment has continued to advance, without interruption, in all SL-401 clinical trials across multiple indications, including the Phase 2 pivotal trial in blastic plasmacytoid dendritic cell neoplasm (BPDCN).
• Given the enrollment trends, the projected timeline for completing enrollment in the final cohort (Stage 3) of the BPDCN pivotal trial remains on track for this quarter.

SL-801

• Patients with advanced solid tumors are currently enrolling into a Phase 1 dose escalation study involving six centers. Four dosing cohorts have been completed, and enrollment in the fifth cohort is ongoing. Further trial updates are expected later this year.

SL-701

• In a Phase 2 trial, adult patients with second-line glioblastoma received SL-701 alone or in combination with bevacizumab. The trial has been completed, and patients are being followed to assess survival. Further updates are expected later this year.

About Stemline Therapeutics Stemline Therapeutics, Inc. is a clinical stage biopharmaceutical company developing novel therapeutics for oncology indications of unmet medical need. A Phase 2 pivotal trial with SL-401, a targeted therapy directed to the interleukin-3 receptor (CD123), is enrolling patients with blastic plasmacytoid dendritic cell neoplasm (BPDCN), an indication for which SL-401 has been granted Breakthrough Therapy Designation (BTD). Additional Phase 2 trials with SL-401 are enrolling patients with other malignancies including high-risk myeloproliferative neoplasms (MPN) and acute myeloid leukemia (AML) in remission with minimal residual disease (MRD). A Phase 1/2 trial with SL-401 in combination with pomalidomide is enrolling patients with relapsed/refractory multiple myeloma. A Phase 1 dose escalation trial is enrolling patients with advanced tumors with SL-801, a novel oral small molecule reversible inhibitor of XPO1. A Phase 2 trial with SL-701, an immunotherapy designed to activate the immune system to attack tumors, is completed and patients are being followed for survival with second-line glioblastoma.

Forward-Looking StatementsSome of the statements included in this press release may be forward-looking statements that involve a number of risks and uncertainties. For those statements, we claim the protection of the safe harbor for forward-looking statements contained in the Private Securities Litigation Reform Act of 1995. The factors that could cause our actual results to differ materially include: the success and timing of our clinical trials and preclinical studies for our product candidates, including site initiation, internal review board approval, scientific review committee approval, patient accrual, safety, tolerability and efficacy data observed, and input from regulatory authorities including the risk that the FDA ultimately does not approve any of our product candidates; our plans to develop and commercialize our product candidates; market acceptance of our products; reimbursement available for our products; our available cash and investments; our ability to obtain and maintain intellectual property protection for our product candidates; our ability to manufacture; the performance of third-party manufacturers, clinical research organizations, clinical trial sponsors and clinical trial investigators; and other risk factors identified from time to time in our reports filed with the Securities and Exchange Commission. Any forward-looking statements set forth in this press release speak only as of the date of this press release. We do not intend to update any of these forward-looking statements to reflect events or circumstances that occur after the date hereof.

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