What happened

Sesen Bio (SESN -2.67%) wasn't a very healthy stock on Thursday. The biotech, which concentrates on developing treatments for cancer, saw its share price dive by nearly 18% on the day. This followed an update on the company's only pipeline drug.

So what

That drug is vicineum, for which Sesen Bio was seeking regulatory approval for the treatment of BCG-unresponsive non-muscle invasive bladder cancer (NMIBC). In August, the company's Biologics License Application (BLA) was rejected by the Food and Drug Administration (FDA). On Wednesday, the company held a Clinical Type A meeting with the regulator to determine a new path forward for vicineum.

Cancer attacking an organism.

Image source: Getty Images.

In its press release published just after the meeting, which Sesen Bio characterized as "productive," the company wrote that it now "believes it has greater clarity regarding the requirements for resubmission of the BLA and the trial design." It added that elements of a potential BLA resubmission for vicineum include a randomized clinical trial in which vicineum's performance is compared to that of an intravesical chemotherapy selected by investors, among other elements.

Now what

"We are pleased to have greater clarity on the regulatory path forward to resubmit the BLA and ultimately bring vicineum to market if approved," Sesen Bio quoted its CEO Thomas Cannell as saying. 

But the FDA's rejection in August generated a storm of controversy, with the company being accused of committing a host of violations in its clinical testing of vicineum. That seriously dampened investor enthusiasm for Sesen Bio stock, sending the company's reputation into a hole it's yet to pull itself out of.

The FDA meeting certainly represents a step forward for the biotech and the drug. But many of those investors clearly aren't convinced Sesen Bio can ultimately deliver the goods with vicineum.