On June 15, 2023 Mersana Therapeutics, Inc. (NASDAQ: MRSN), a clinical-stage biopharmaceutical company focused on discovering and developing a pipeline of antibody-drug conjugates (ADCs) targeting cancers in areas of high unmet medical need, reported that the U.S. Food and Drug Administration (FDA) has issued a partial clinical hold pausing new patient enrollment in UP-NEXT and UPGRADE-A, the company’s ongoing clinical trials of UpRi in platinum-sensitive ovarian cancer (Press release, Mersana Therapeutics, JUN 15, 2023, View Source [SID1234632729]). UPLIFT, Mersana’s ongoing clinical trial of UpRi in platinum-resistant ovarian cancer, completed enrollment in October 2022. Patients who are already enrolled in these trials may continue receiving UpRi. Mersana expects to lock its UPLIFT clinical trial database and disclose UPLIFT top-line data by early August.

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The partial clinical hold follows a submission by Mersana of a recent aggregate safety report of all patients dosed with UpRi (approximately 560 patients) evaluating bleeding events. As noted in FDA guidance, aggregate analyses generally become more informative as a drug progresses through development and accumulates data. Detection of a clinically meaningful risk, particularly in single-arm clinical trials, typically requires a large safety database to detect differences in rates of adverse events compared to those that are expected in the population being studied.

Although data on the background rate of bleeding in platinum-resistant ovarian cancer are limited, Mersana’s recent assessment determined that serious bleeding events appear to occur at a higher rate than background. While most bleeding cases in this aggregate safety analysis were low-grade, five (<1%) Grade 5 (fatal) bleeding events were observed among the approximately 560 patients dosed to date. The causes of bleeding events remain under investigation.

"Patient safety is always at the forefront for us, and work is now underway to compile further analyses that may inform FDA," said Anna Protopapas, President and Chief Executive Officer of Mersana Therapeutics. "Additionally, with UPLIFT top-line data on the near-term horizon, we will soon have a much more complete assessment of both the efficacy and safety profile for UpRi in platinum-resistant ovarian cancer."

The company is awaiting the FDA’s written correspondence regarding the partial clinical hold and expects the FDA will request a comprehensive assessment of UpRi safety data, inclusive of bleeding events. In addition, Mersana plans to submit to the FDA the UPLIFT safety and efficacy data once available. The company plans to seek alignment with the FDA to lift the partial clinical hold and resume enrollment in UP-NEXT and UPGRADE-A.