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.

Let's take a look at three stocks -- Halozyme (NASDAQ:HALO), Exelixis (NASDAQ:EXEL), and VIVUS (NASDAQ:VVUS) -- which could all loom large in biotech headlines this morning.

Halozyme announces positive data from a phase 1/2 trial of HTI-501
Halozyme just announced top-line data from a proof of concept phase 1/2 trial evaluating the use of HTI-501, which met its primary endpoint. HTI-501 is intended to reduce cellulite (edematous fibrosclerotic panniculopathy), indicating that it could attract interest from the pharmaceutical cosmetics industry, which is dominated by Botox maker Allergan and its competitor Valeant Pharmaceuticals. The phase 1/2 trial demonstrated a statistically significant mean improvement of 53% in 36 evaluable patients after 28 days of treatment.

Halozyme is best known for Enhanze, an enzyme which temporarily breaks down a natural substance beneath the surface of the human skin, thereby improving the delivery of injectable biologics subcutaneously. Halozyme's major collaborators include Roche, Pfizer, Baxter, Shire's ViroPharma, and Intrexon. Roche notably used Halozyme's Enhanze to create a SC version of its best-selling breast cancer drug Herceptin -- shortening the requisite 30 to 90 minutes for an IV injection to a mere two to five minutes.

Exelixis' Cometriq is approved for MTC in Europe
Exelixis just announced the European approval of Cometriq, its only marketed product, for the treatment of adult patients with progressive, unresectable, locally advanced or metastatic medullary thyroid carcinoma (MTC). Swedish Orphan Biovitrum (Sobi) signed a deal with Exelixis in February 2013 to support the commercialization of Cometriq in the European Union through the end of 2015.

Cometriq, which was approved by the FDA in November 2012 and launched in January 2013, generated $15 million in sales in fiscal 2013, accounting for 48% of the company's revenue. The remainder of Exelixis' top line was generated from collaboration and license revenues.

Since late-stage MTC only accounts for 3% to 4% of all thyroid cancers, peak sales estimates for Cometriq based on MTC alone are fairly low at $50 million. However, $50 million indicates that Cometriq still has room to run as Exelixis continues testing the drug in phase 3 trials for prostate cancer, hepatocellular carcinoma, renal cell carcinoma.

If approved for prostate cancer, the outlook for Cometriq (also known as cabozantinib or XL184) completely changes, with analysts at Goldman Sachs projecting peak sales estimates of $1.6 billion -- meaning that, if all goes well for the company long term, Exelixis could be seen as undervalued at current prices.

VIVUS claims that a new article suggests blood pressure benefits for Qsymia
Last but not least, obesity drug maker VIVUS just announced that a recent article from the Journal of Hypertension, the official publication of the International Society of Hypertension and the European Society of Hypertension, reinforced the cardiovascular benefit-risk profile of its obesity drug Qsymia.

VIVUS claims that the data suggests that Qsymia is a safe and effective weight loss treatment for patients with cardiovascular risks related to hypertension and type 2 diabetes. The study, which examined data from two previously conducted studies of Qsymia, found that the weight loss achieved by recommended and top doses of Qsymia was associated with significant reductions in blood pressure.

That's definitely a positive development, but investors should remember that Qsymia is already approved in the U.S. for overweight (BMI of 27 kg/m2 or greater) and obese (BMI of 30kg/m2 or greater) patients diagnosed with at least one weight-related medical condition such as high cholesterol, high blood pressure, or type 2 diabetes. However, both Qsymia and a rival drug, Arena (NASDAQ:ARNA) and Eisai's Belviq, haven't lived up to Wall Street's blockbuster peak projections.

VIVUS reported $23.7 million in Qsymia sales in fiscal 2013, while Arena reported $5.7 million in Belviq revenue. In addition to Qsymia, VIVUS markets the erectile dysfunction drug Stendra/Spedra, which is being commercialized by Auxilium and Sanofi.

Shares of VIVUS have fallen nearly 50% over the past 12 months.

Boost your 2014 returns with The Motley Fool's top stock
There's a huge difference between a good stock and a stock that can make you rich. The Motley Fool's chief investment officer has selected his No. 1 stock for 2014, and it's one of those stocks that could make you rich. You can find out which stock it is in the special free report "The Motley Fool's Top Stock for 2014." Just click here to access the report and find out the name of this under-the-radar company.

Leo Sun has no position in any stocks mentioned. The Motley Fool recommends Baxter International, Exelixis, and Valeant Pharmaceuticals. The Motley Fool owns shares of Exelixis. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.