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 biotech developer Puma Biotechnology (NYSE:PBYI) fell by as much as 13% today as investors backed off from the stock's astronomical run-up of more than 300% yesterday following a clinical trial success of the company's HER2-positive breast cancer therapy neratinib.

So What: Investors raked in profits today after Puma dominated the market yesterday, scoring a victory in a phase 3 study of neratinib that sent analysts rushing to raise price targets on Puma's stock. It was a victory for patient shareholders who had waded through a downbeat 2014 for Puma, as neratinib now looks like a blockbuster in the wings for this company after the drug boosted disease-free survival in patients with early stage HER2-positive breast cancer by 33 % as compared to a placebo.

Now What: While it's tempting to take profits from this sky-high stock, the best may be yet to come from Puma. The company's aiming to seek regulatory approval in the first half of next year, and FDA clearance now looks like a near-lock after the trial data surprised even the most optimistic of analysts following the stock. Wall Street's pegged the drug's peak sales at anywhere from $1 billion to as high as $6 billion down the road, and if Puma can deliver more upbeat surprises with this drug in the future, investors who stay patient today could wind up with even bigger gains down the road.

A takeover possibility now looks considerably more likely, as blockbuster-hungry big pharmas gunning for growth could use a drug with neratinib's potential. While Puma's stock delighted the biotech world yesterday, more may be on the way down the road for patient investors willing to hold off on taking profits.

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.