Sesen Bio Shares Plunge Despite Reporting Positive Interim Phase III Results

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Shares of newly dubbed Sesen Bio (formerly Eleven Biotherapeutics) have plunged 23 percent after the company released positive, three-month data from its ongoing Phase III high-grade non-muscle invasive bladder cancer (NMIBC) trial.

On Monday Cambridge, Mass.-based Sesen said its antibody-drug conjugate (ADC) therapeutic Vicinium was able to help patients achieve a 42 percent complete response rate at three months. Patients in the trial had been previously treated with bacillus Calmette-Guérin (BCG) but have relapsed or did not respond to that first-line treatment. The three-month data from the Phase III trial was revealed at the American Urological Association Annual Meeting in San Francisco.

The Phase III trial includes 111 patients with high-grade NMIBC that is either carcinoma in situ (CIS), which is cancer found on the inner lining of the bladder that has not spread into muscle, or patients with papillary disease without CIS, which is cancer that has grown from the bladder lining out into the bladder, but has not spread into muscle. For patients who fail to respond to BCG the next step in treatment is often a cystectomy, the removal of the bladder, as well as other areas that contain cancer.  Rian Dickstein, chief of urology, University of Maryland Baltimore Washington Medical Center and a principal investigator in the Sesen trial, said he has been impressed with the safety and efficacy from the three-month data and believes Vicinium could be brought forward as a safer and less radical treatment than cystectomy.

The therapeutic was well tolerated, with 72 percent of adverse events being mild, Grade 1 or Grade 2. The most common adverse events were urinary tract infection, dysuria, fatigue, diarrhea, nausea or micronutrition urgency.

Bladder cancer is the sixth most common cancer in the United States, with about 80,000 annual diagnoses. Of those new cancer patients, Sesen said between 70 percent and 80 percent of those are NMIBC, which could provide a good market for the company. Approximately half of those bladder cancer patients do not respond to BCG. The majority of the patients, Sesen said, are over the age of 70 years. Providing those elderly patients with an option other than surgery would be appealing.

Vicinium was developed using the company’s proprietary Targeted Protein Therapeutics platform. The therapy 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.

Sesen Chief Executive Officer Stephen Hurly said the three-month data is encouraging for the company, particularly given its new branding.

“We have made tremendous progress over the last several years to get us to where we are today, and I am proud of what our team has accomplished. Our new name is a reflection of the journey we’ve taken to get to this point and represents our mission of improving lives,” Hurly said in a statement.

Twelve-month data is anticipated in mid-2019, the company said.

In a conference call following the release of the data Hurly said if the data continues to be positive, he is confident that the company has a strong path to regulatory approval.

Despite the positive news through, shares plunged, particularly as analysts on the call expressed some concern over previous efficacy reports and new guidance for approval from the U.S. Food and Drug Administration. Hurly though seemed confident that the data from the trial, should it continue to be positive, would be well within the FDA guidelines. 

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