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.

Shares in Puma Biotechnology (NASDAQ:PBYI) continued to slide today after it presented less-than-inspiring cancer trial results at the ASCO conference in Chicago.

So what
Puma Biotechnology is the epitome of a hit-and-miss stock. Its lead (and only) drug under development is neratinib, a therapy being studied for use in breast cancer.

At ASCO, Puma Biotechnology offered up trial results showing that HER-2 positive breast cancer patients taking neratinib only saw a slight improvement in two-year invasive disease free survival versus placebo.

In this phase 3 trial, patients who had been previously treated with Herceptin were randomized to either receive neratinib as an adjunctive therapy or a placebo. Of those taking neratinib, 93.9% were disease-free two years after treatment, which slightly edged out the 91.6% rate in the placebo arm of the study. That advantage may not be enough to justify neratinib's use in this indication, given that a lot of neratinib patients have to endure diarrhea as a side effect.

Now what
Puma Biotechnology's investors have high hopes for neratinib, especially given that Puma Biotechnology's founder is Alan Auerbach. Auerbach was behind Zytiga, a prostate cancer drug that was developed by Cougar Biotechnology, which Auerbach sold to Johnson & Johnson in 2009 for $1 billion.

However, those hopes may have been dashed by these trial results, especially since Puma Biotechnology reported in December that it would change the indication for a planned neratinib FDA filing from HER-2 metastatic breast cancer to extended adjuvant treatment of HER-2 positive early stage breast cancer. That change pushed back Puma Biotechnology's timeline for a neratinib filing from 2015 to early 2016. 

While the data from this trial isn't as strong as many had hoped, it doesn't mean that neratinib is destined for the dustbin. Puma Biotechnology is conducting a slate of studies on the drug that could pan out, and if they do, then a suitor could still come knocking. Having said that, although shares have retreated from all-time highs of nearly $280 to current levels around $145, Puma Biotechnology's market cap is still $4.7 billion, and for that reason, I'm content to stay on the sidelines a bit longer on this one.