What happened

Shares of the mid-cap biotech Immunomedics (NASDAQ:IMMU) were down by 12% as of 1:20 p.m EDT today on heavy volume. Why are investors running for the door today?

Immunomedics shares are falling in response to the company's clinical update at the 2019 European Society for Medical Oncology (ESMO) Congress over the weekend. Specifically, the biotech unveiled interim data at the conference from a midstage study evaluating sacituzumab govitecan (SG) in patients with advanced urothelial cancer (bladder cancer) who have relapsed or are refractory to immune checkpoint inhibitors and platinum-based chemotherapy. The drug reportedly achieved a 29% overall response rate (ORR) during this preliminary peek at the data.

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Image source: Getty Images.

So what

While a 29% ORR for advanced bladder cancer isn't a shabby outcome by any stretch of the imagination, investors seem to be concerned that Seattle Genetics (NASDAQ:SGEN) may have a more potent candidate for this high-value indication.

During the same conference, Seattle Genetics presented data for its combo therapy, consisting of enfortumab vedotin and Merck's Keytruda, as a treatment for previously untreated bladder cancer in patients with locally advanced or metastatic disease who were ineligible for treatment with cisplatin-based chemotherapy. This combo therapy reportedly produced a 71% confirmed objective response rate in the study.  

Now what

Should investors hit the panic button? Certainly not. There should be plenty of room for both treatments once the dust settles. Also, Seattle Genetics' ORR in advanced bladder cancer could perk up as the data mature. Put simply, the market appears to be overreacting to this preliminary peek at Seattle Genetics' bladder cancer data.    

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.