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 the recently volatile Northwest Biotherapeutics (NASDAQ:NWBO), a clinical-stage biopharmaceutical company developing immunotherapeutic options to treat cancer, dipped as much as 21% after receiving a downgrade before the opening bell.

So what: Research firm Oppenheimer dropped Northwest Biotherapeutics, known also as NW Bio, to perform from outperform, with valuation cited as the primary concern. Oppenheimer said it believes the recent run-up has fairly valued NW Bio's assets, including its DCVax immunotherapeutic pipeline.

If you recall, this week's stock rise came on the heels of two special approvals in Germany -- a hospital exemption and approval for insurance reimbursement -- which will allow DCVax-L to be given to German patients with glioma brain cancers. In return, NW Bio will be able to charge a full price for the medication and be reimbursed through sickness funds (i.e., insurance companies). DCVax-L is being tested in a phase 3 trial in the U.S. for glioblastoma multiforme, or GBM, the most lethal form of brain cancer, but the German five-year approval allows DCVax-L to be used on all glioma brain cancers in that country.

Now what: I'm certainly not surprised to see the downgrade after the monstrous run NW Bio had from receiving what amounts to a temporary approval in Germany. I continue to believe that its U.S. phase 3 study is what will matter most, since analysts will be looking toward the strictly regulated Food and Drug Administration for direction as to DCVax-L's potential, at least in treating GBM. This isn't to say that NW Bio isn't headed in the right direction with its pipeline, or that some move higher wasn't due given its two special exemptions, but the upside appeared very limited following its recent two-day move higher.

Northwest Biotherapeutics has soared this year -- but even it may struggle to keep up with this top stock when all is said and done
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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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