The Food and Drug Administration (FDA) has issued a Complete Response Letter (CRL) to Sesen Bio regarding its Biologics License Application (BLA) for Vicineum (oportuzumab monatox-qqrs) for the treatment of bacillus Calmette-Guérin (BCG)-unresponsive non-muscle invasive bladder cancer (NMIBC).

The FDA’s letter requested that the Company provide additional clinical and statistical data and analyses prior to another review. The Agency also noted CMC (Chemistry, Manufacturing and Controls) issues pertaining to a recent pre-approval inspection.

Vicineum is an investigational locally administered recombinant fusion protein that targets epithelial cell adhesion molecule antigens on the surface of tumor cells to deliver Pseudomonas Exotoxin A. The fusion protein design is expected to reduce the risk of toxicity to healthy tissue, thereby improving safety. The BLA included preliminary findings from the phase 3 VISTA trial ( Identifier: NCT02449239), which demonstrated a strong benefit-risk profile for Vicineum in 133 adults with high-risk, BCG-unresponsive NMIBC. 

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“We are deeply disappointed by this unexpected result, and it is an unfortunate day for patients suffering from BCG-unresponsive NMIBC,” said Dr Thomas Cannell, president, and CEO of Sesen Bio. “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.”


  1. Sesen Bio receives Complete Response Letter from FDA for Vicineum™ (oportuzumab monatox-qqrs). News release. Sesen Bio. Accessed August 16, 2021.
  2. Sesen Bio submits completed Biologics License Application to the FDA for Vicineum™ and has requested Priority Review. News release. Sesen Bio. Accessed August 16, 2021.

This article originally appeared on MPR