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 Puma Biotechnology (NYSE:PBYI), a clinical-stage biopharmaceutical company developing therapies to treat various forms of cancer, jumped higher by as much as 58% after reporting positive top-line results from its phase 2 I-SPY 2 trial with PB272 (known scientifically as neratinib) as a neoadjuvant treatment for stage 2 or higher breast cancer.

So what: According to Puma's press release from yesterday, in its randomized 300-patient confirmatory trial, neratinib -- when combined with paclitaxel and followed by doxorubicin and cyclophosphamide -- should demonstrate a high rate of success in late-stage trials with the HER2-positive/HR-negative signature. Within this grouping, the neratinib arm delivered a p-value of 0.053, or a 94.7% probability of superiority over the current standard of treatment according to Bayesian predictive models. Furthermore, neratinib-based regimens demonstrated a Bayesian probability of superiority over paclitaxel plus Herceptin of 78.1% if they were to go head to head in a phase 3 trial.

Now what: Simply put, no one really expected Puma's results to be this strong, which is why we're seeing such a monstrous move to the upside. Not to sound like a broken record, but I would still like to see the full data before stating my full opinion on Puma (the company will release its full data at a scientific meeting in the future). I've witnessed far too many cancer drugs demonstrate promise in mid-stage trials only to disappoint in late-stage trials, so my thought at the moment is that sticking to the sidelines until we're well into late-stage trials might be the smartest course of action.

Fool contributor 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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