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 Oncothyreon (NASDAQ:ONTY), a developmental biotech, climbed more than 13% today, while fellow biotech stocks OncoMed (NASDAQ:OMED) and Array BioPharma (NASDAQ:ARRY) roared higher by as much as 10% and 16.4%, respectively, following a positive trial result from Puma Biotechnology's HER2-positive breast cancer therapy neratinib.

So What: Neratinib's astronomical success in a phase 3 trial for increasing disease-free survival in early stage HER2-positive breast cancer by 33 % as compared to a placebo as sent shock waves throughout the biotech industry. Wall Street's pushed stocks of fellow clinical-stage HER2-positive breast cancer drug developers higher on the day in light of the positive trial data. Array and Oncothyreon collaborate on ARRY-380, a phase 1 candidate for treating the disease, while OncoMed is developing vantictumab, which last year launched a phase 1b trial targeting HER2-positive breast cancer. OncoMed did

Now What: Puma might be looking to file for approval next year for neratinib after the success, but OncoMed, Oncothyreon, and Array are in much earlier-stage trials for their own HER2-positive cancer treatments. Still, the strong showing by neratinib has lifted confidence across the biotech sector that agents specifically targeting the HER2 growth factor have a major place as a lucrative adjuvant treatment.

While OncoMed, Oncothyreon, and Array still have a long way to go to showing similar gains from their own therapies, this is a market worth pursuing: Analysts have pegged neratinib as racking up $4 billion or more in peak sales if cleared by the FDA, with an 85% chance at regulatory approval.

Dan Carroll has no position in any stocks mentioned. The Motley Fool has no position in any of the stocks mentioned. 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.