Sesen’s PhIII bladder cancer data send stock south as investors fret over safety

Following a branding makeover just last week, Sesen Bio (which used to go by Eleven Biotherapeutics) has published three-month data for its bladder cancer drug Vicinium. The results have some investors cautious, as the company’s stock — trading under the freshly minted ticker symbol $SESN — is down 23% since the announcement.

Stephen Hurly

Sesen was little more than a shell with a bank account a couple years ago after its lead drug failed twice and it completed a deal to license out its remaining program to Roche. But then the entity acquired Toronto-based Viventia, snagging its now lead drug candidate Vicinium, a next-gen antibody-drug conjugate to treat high-grade non-muscle invasive bladder cancer.

The new Vicinium data came from an ongoing Phase III trial called Vista, which enrolled 133 patients with high-grade NMIBC. These patients had previously been on BCG immunotherapy, a standard treatment that doesn’t always deliver, said Rian Dickstein, an investigator in the trial.

“For those patients who relapse or who don’t respond at all, the standard alternative is radical cystectomy,” Dickstein said in a statement. “In a cystectomy, the bladder is removed along with surrounding lymph nodes and other organs that contain cancer.”

Rian Dickstein

Vicinium is a hopeful alternative to losing the bladder. 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.

The company said EpCAM is overexpressed in NMIBC but not in healthy bladder cells, so homing in on it will hopefully decrease toxic effects in healthy tissues.

Sesen’s efficacy data, which came from 111 patients with cancer that had not spread from the bladder into muscle or other tissue, showed that Vicinium had a complete response rate of 43%.

Four serious adverse events related to the treatment were reported in the data, including acute kidney injury or renal failure and cholestatic hepatitis, the company said. But 72% of the adverse events were classed as grade 1 or 2.

Still, the serious adverse events appear to have some investors worried, with the company’s stock dropping from $3.00 per share to $2.30 by Monday’s close.

Stephen Hurly, the company’s president and CEO, said the data are encouraging.

“The Vista trial three-month data are encouraging for our company and the patients with high-grade NMIBC who have been underserved for many years,” Hurly said. “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. With 12-month data expected by mid-2019, we are continuing to advance Vicinium to assess its full potential in treating this devastating cancer.”

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Research Scientist - Immunology
Recursion Pharmaceuticals Salt Lake City, UT
Director of Operations
Atlas Venture Cambridge, MA

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