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 this three top stocks -- Prosensa (NASDAQ: RNA), Medivation (MDVN), and Alcobra (NASDAQ: ADHD) -- all of which could loom large in biotech headlines this morning.

Prosensa in good shape on encouraging phase 2 data for its DMD drug
Prosensa is up 23% in premarket this morning after the company reported encouraging data from a phase 2 study for drisapersen, its lead drug candidate for Duchenne muscular dystrophy (DMD). DMD is a rare genetic disorder which causes muscular degeneration and death in 1 out of 3,500 boys.

Yesterday, Prosensa announced that in its 48-week study of 51 boys with DMD, the drisapersen group experienced stabilization and improvements in muscle function and physical activity for the 24-week period, then maintained that improvement during the 24-week follow-up phase.

This is a rare positive development for Prosensa, which has fallen more than 60% over the past 12 months after a series of major setbacks. Last September, Prosensa and its partner GlaxoSmithKline (NYSE: GSK) announced that its phase 3 trial for drisapersen missed its primary endpoint. GSK subsequently terminated their partnership and handed the drug back to Prosensa in January.

Prosensa's primary rival, Sarepta Therapeutics (SRPT -1.11%), has also been highly volatile over the past 12 months, after the FDA recommended against an accelerated approval of its DMD drug, eteplirsen, based on phase 2b data from 12 patients. 

Prosensa also announced its full year financial results. The company, which does not have any marketed products, reported that its cash and equivalents climbed 102% year-over-year to $114 million, mainly due to about $89 million in proceeds from issuing 6.9 million shares of common stock from its IPO last July.

Medivation and Astellas submit an sNDA for the approval of Xtandi for chemo-naive patients
Meanwhile, Medivation and Astellas Pharma just submitted a supplemental New Drug Application (sNDA) to the FDA for its prostate cancer drug Xtandi for men with metastatic castration-resistant prostate cancer (mCRPC) who have not been treated with chemotherapy.

The sNDA was based on positive data from the phase 3 PREVAIL trial evaluating the drug against a placebo in more than 1,700 chemotherapy-naive patients. A marketing authorization application (MAA) for the same indication is expected to be submitted to the European Medicines Agency later this year.

Xtandi has been approved in the U.S. and Europe as a oral treatment for mCRPC patients who have been previously treated with docetaxel, a common chemotherapy treatment. The drug's chief competitor, Johnson & Johnson's (JNJ 2.58%) Zytiga, was approved for chemotherapy-naive mCRPC patients in the U.S in December 2012 and in the EU in January 2013. As a result of those additional indications, sales of Zytiga soared 77% year-over-year to $1.7 billion in fiscal 2013.

Xtandi hasn't sold nearly as well as Zytiga, due to fewer approved indications and a monthly price tag of $7,450 compared to $5,500 for Zytiga. The overall survival rates of the two drugs are similar, but Xtandi is considered slightly safer, since patients don't need to take an additional medication (prednisone) to offset the risk of high blood pressure which can be caused by Zytiga. Astellas and Medivation jointly develop and commercialize Xtandi in the U.S., while Astellas manufactures and commercializes the drug overseas.

Alcobra's phase 3 trial for its adult ADHD medication enrolls its first patient
Last but not least, Alcobra just announced that the first patient has been enrolled in a phase 3 clinical trial of MDX (metadoxine extended release) for the treatment of adult ADHD (attention deficit hyperactive disorder). The randomized, placebo-controlled trial is expected to include 300 patients across 20 locations in the United States and Israel, and is expected to conclude in the second half of 2014.

Alcobra's IND (investigational new drug) application for MDX was accepted by the FDA earlier this month. The drug has also been designated MDX as an orphan drug for Fragile X syndrome, a genetic syndrome which causes autism in boys. Alcobra has noted that a preclinical abuse study demonstrated that MDX has less potential for abuse than the commonly used ADHD medication methylphenidate (commonly known as Ritalin).

If succesfully approved for adults and eventually children, MDX could be a strong competitor against Shire's Vyvanse and Adderall XR, J&J's Concerta, and Eli Lilly's Strattera -- which all have past or future peak sales estimates between $600 million and $1.6 billion.

Alcobra does not have any marketed products, and finished last quarter with about $50 million in cash and equivalents.