Investors in pharmaceutical stocks are all too familiar with the volatility that can be caused by the outcome of clinical trials. Sometimes it can be extremely positive news that causes shares to kick on to new highs, while at other times it can be disappointing news that leaves investors feeling despair at the falling share price.

This, it seems, simply comes with the territory of investing in pharmaceutical stocks. However, sometimes disappointment from a clinical trial can have a rather mooted effect on the share price. For instance, Pfizer (PFE 0.66%) announced last week that a possible treatment for an advanced form of lung cancer missed its primary objectives in a couple of late-stage studies.

The drug in question is called Dacomitinib, and it was unable to show a statistically significant improvement in progression-free survival when compared with another drug, Erlotinib. This occurred in two separate studies (although in the second study a placebo was used instead of Erlotinib), and the disappointing thing about the two trials is that they were both late-stage trials.

Therefore, this is one of the final hurdles before submitting the drug for approval, and to obtain such results from two trials is disappointing to say the least.

However, shares didn't react too strongly to the news, possibly because Pfizer announced that it's still waiting for the results of a third trial involving the drug. These results aren't due out until 2015, which should give Pfizer time to move further down the line with the restructuring it discussed in its recent fourth-quarter results.

While there was disappointment for Pfizer, pharmaceutical peer GlaxoSmithKline (GSK -0.07%) has enjoyed something of a purple patch at the start of 2014, as it has received positive news flow for three different drugs thus far.

The first was HIV treatment Tivicay, which the European Commission granted approval for use by adults and adolescents above 12. The second was Eperzan, which received a positive opinion from the Committee for Medicinal Products for Human Use in Europe, while the third was the meeting of the primary endpoint by a combination of Tafinlar and Mekinist in a phase 3 trial.

GlaxoSmithKline isn't the only pharmaceutical company that's had some encouraging news flow with regard to its drug pipeline in 2014. The diabetes alliance between Bristol-Myers Squibb (BMY -0.72%) and AstraZeneca (AZN 0.46%), which has now been bought outright by AstraZeneca for around $4 billion, has received approval for two drugs in 2014: Farxiga in the U.S. and combination drug Xigduo in the European Union.

Of course, it must be pointed out that it's not all bad news for Pfizer. It's a partner (along with GlaxoSmithKline and Shionogi) in the ViiV Healthcare joint venture through which the aforementioned Tivicay HIV drug was granted European Commission approval. Furthermore, the diabetes alliance between Bristol-Myers Squibb and AstraZeneca has produced two approvals in 2014 but has been heavily criticized for its high costs and lack of tangible results, leaving some commentators to suggest that AstraZeneca has overpaid for Bristol-Myers Squibb's share.

Therefore, while disappointment in a late-stage trial is clearly not good news for Pfizer, the ups and downs of drug approval is something that comes with the territory of being a pharmaceutical company. Of keener interest for the long-term fortunes of Pfizer is how successful its restructuring program is, with the ups and downs of drug approvals taking second place at the moment.