Sesen Bio Reports Positive, Preliminary Data Update from Trial for Bladder Cancer

Sesen Bio reported updated, preliminary primary and secondary endpoint data from the Company’s Phase 3 VISTA trial further supporting the strong benefit-risk profile of Vicinium for the potential treatment of patients with high-risk, bacillus Calmette-Guérin (BCG) unresponsive, non-muscle invasive bladder cancer (NMIBC). The updated preliminary Phase 3 clinical data will serve as the basis for the anticipated initiation of the Company’s BLA submission in 4Q 2019.

 "After two very positive meetings with the FDA in the second quarter, we are now focused on initiating the BLA submission for Vicinium in the fourth quarter under an Accelerated Approval pathway with Rolling Review," said Dr. Thomas Cannell, president and chief executive officer of Sesen Bio. "We believe this regulatory pathway and our strong 12-month Phase 3 data could potentially expedite patient access to Vicinium, which is particularly important in light of the ongoing BCG shortage. We look forward to our two additional face-to-face meetings with the FDA in the fourth quarter as we work to bring Vicinium to market to help save and improve the lives of patients with NMIBC."

Updated Primary and Secondary Endpoint Data from Phase 3 VISTA Trial Support a Growing Body of Evidence Demonstrating the Clinically Meaningful Anti-tumor Activity of Vicinium: In May, Sesen Bio announced updated preliminary data from its ongoing Phase 3 VISTA trial, a single-arm, 24-month, multi-center clinical trial designed to support the approval of Vicinium for the treatment of patients with high-risk, BCG-unresponsive NMIBC. The trial completed registration in the second quarter of 2018, with a total of 133 patients across three cohorts based on histology and time to disease recurrence after adequate BCG treatment (at least two courses of BCG with at least five doses in the first course and two doses in the second course). Primary efficacy endpoints consist of complete response rate and duration of response for patients in Cohort 1. Secondary efficacy endpoints include time to disease recurrence for patients in Cohort 3, and time to cystectomy, progression-free survival, event-free survival, and overall survival for patients across all cohorts.

Vicinium, a locally-administered fusion protein, is Sesen Bio’s lead product candidate being developed for the treatment of high-risk non-muscle invasive bladder cancer (NMIBC). Vicinium is comprised of a recombinant fusion protein that targets epithelial cell adhesion molecule (EpCAM) antigens on the surface of tumor cells to deliver a potent protein payload, Pseudomonas Exotoxin A. Vicinium is constructed with a stable, genetically engineered peptide tether to ensure the payload remains attached until it is internalized by the cancer cell, which is believed to decrease the risk of toxicity to healthy tissues, thereby improving its safety. In prior clinical trials conducted by Sesen Bio, EpCAM has been shown to be overexpressed in NMIBC cells with minimal to no EpCAM expression observed on normal bladder cells. Sesen Bio is currently conducting the Phase 3 VISTA trial, designed to support the registration of Vicinium for the treatment of high-risk NMIBC in patients who have previously received a minimum of two courses of bacillus Calmette-Guérin (BCG) and whose disease is now BCG-unresponsive. Additionally, Sesen Bio believes that cancer cell-killing properties of Vicinium promote an anti-tumor immune response that may potentially combine well with immuno-oncology drugs, such as checkpoint inhibitors. The activity of Vicinium in BCG-unresponsive NMIBC is also being explored at the US National Cancer Institute in combination with AstraZeneca’s immune checkpoint inhibitor durvalumab.

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