Although we don't believe in timing the market or panicking over market movements, we do like to keep an eye on big changes -- just in case they're material to our investing thesis.

What: Shares of Immunomedics (NASDAQ:IMMU), a clinical-stage developer of monoclonal antibodies to treat cancer and autoimmune disorders, jumped as much as 10% after announcing that it received orphan drug designation for small-cell lung cancer experimental drug IMMU-132.

So what: According to the press release, IMMU-132, the company's antibody-drug conjugate therapy designed to treat solid tumors, received orphan drug status from the Food and Drug Administration. Orphan status affords IMMU-132 some special perks, including tax credits for qualified clinical testing, a waiver for the User Fee if it files for a new drug application, and most importantly, a seven-year period of marketing exclusivity if it's approved.

Now what: Most biotech and biotech savvy investors only think of either Seattle Genetics or ImmunoGen when it comes to antibody-drug conjugate developers, but they should also keep Immunomedics in mind. As a quick refresher, ADC compounds piggyback a chemotherapy toxin onto an antibody and release this toxin when it comes in contact with a specific protein from a targeted cancer cell. In other words, it's engineered to deliver a more precise dosing of toxins to cancer cells while doing significantly less harm to healthy cells. Standard chemotherapy doesn't differentiate between healthy and cancerous cells. Although IMMU-132 is very early in its development, the potential for partnerships is huge as we've seen from ImmunoGen, and the number of potential types of cancer it may work on is also large. I would definitely suggest you keep an eye on Immunomedics.

Fool contributor Sean Williams has no material interest in any companies mentioned in this article. You can follow him on CAPS under the screen name TMFUltraLong, track every pick he makes under the screen name TrackUltraLong, and check him out on Twitter, where he goes by the handle @TMFUltraLong.

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