2021-08-16| Trials & Approvals

FDA Rejects Sesen Bio’s Bladder Cancer Drug Application, Asks Additional Data

by Judy Ya-Hsuan Lin
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On August 13th, Cambridge, MA-based Sesen Bio announced that the FDA has sent a complete response letter to its BLA for Vicineum (oportuzumab monatox), a bladder cancer drug. The agency has requested additional clinical and statistical data and analyses of the therapeutics. Since the news, Sesen Bio’s stock dropped to $1.21 per share at close on Friday.

Sesen expressed their disappointment, pointing out that they have regularly met with the FDA for the past two years and honored their guidance to push Vicineum to the next level—treating high-risk, BCG-unresponsive (bacillus Calmete-Guérin) non-muscle invasive bladder cancer (NMIBC).

“We are deeply disappointed by this unexpected result, and it is an unfortunate day for patients suffering from BCG-unresponsive NMIBC,” Thomas Cannell, DVM, president, and CEO of Sesen. “We remain dedicated to our mission to save and improve the lives of patients by bringing new treatment options to patients, and we intend to work closely with the FDA to understand next steps.”



Sesen Bio is a late-stage clinical company developing targeted fusion protein therapeutics for the treatment of patients with cancer. Its lead candidate, Vicineum, is an antibody drug conjugate (ADC) in which a recombinant fusion protein targets epithelial cell adhesion molecule (EpCAM) antigens on the surface of tumor cells to deliver a potent protein payload, Pseudomonas Exotoxin A.

Vicineum is believed to work effectively with immuno-oncology drugs, such as checkpoint inhibitors, due to its anti-tumor immune response. To ensure the safety of use and to limit its toxicity, Vicineum is constructed as a stable genetically engineered peptide tether to guarantee the payload remains attached until internalized by the cancer cell.


Phase 3 VISTA Trial

The open-label, single-arm, multicenter VISTA trial enrolled 133 adult patients with carcinoma in situ and/or high-grade (Ta and T1) papillary disease who were unresponsive to prior treatment with BCG with or without interferon. Enrollees were required to have completed at least two courses of full-dose BCG, with at least five doses in the first course and two doses in the second course, and experience disease recurrence within 30 weeks from the last BCG treatment for those with papillary NMIBC or within 50 weeks for those with CIS (clinically isolated syndrome).

In preliminary findings from the trial, Vicineum demonstrated positive antitumor activity in patients with high-risk, BCG-unresponsive NMIBC across three cohorts: patients with carcinoma in situ with or without papillary disease that was refractory or recurred six months of BCG treatment, with or without papillary diseases that were recurred between six to eleven months of BCG treatment, or with the papillary disease only that were recurred within six months of BCG treatment.

One of the primary endpoints of the study was complete response (CR), and across two of the three study cohorts, patients with carcinoma in situ who had received prior BCG therapy achieved a CR rate of 28% at six months and 17% at 12 months.

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