The past two weeks have been very good to biopharmaceutical firm ImClone Systems (NASDAQ:IMCL). Shares of the cancer drugmaker have been up nearly 25% since news of a setback on a competing product from Amgen (NASDAQ:AMGN). Yesterday, shares were pushed up on ImClone's announcement that a recently completed Erbitux clinical trial was successful.

ImClone's only marketed drug is the cancer treatment Erbitux, which is partnered with Bristol-Myers Squibb (NYSE:BMY). Currently Erbitux is indicated as a treatment for colorectal cancer and head and neck cancer, but is usually prescribed at the later stages of the diseases when other therapies haven't been successful. To ramp up sales of the drug, ImClone has been testing the use of Erbitux in earlier disease settings with different therapies. The drugmaker announced today that Erbitux plus chemotherapy improved overall survival in patients with head and neck cancer versus those not getting the drug. No statistics from the clinical trial were announced, though; they are being saved for presentation at a major medical conference.

Considering that there are some quality-of-life issues, such as allergic reactions and rash, that can be associated with Erbitux, it is really the degree of the efficacy data from this study that matters, and not only that the trial met its primary endpoint. Just the fact that the primary endpoint of improving overall survival was statistically significant (which is all we know from this press release) for the Erbitux plus chemotherapy group versus placebo is not enough for this clinical trial to be considered a success from a marketing and sales point of view.

Any survival benefit with Erbitux's use is obviously a good thing. But a mediocre improvement on this endpoint will not drive increased patient demand for this treatment for head and neck cancer.

Sales of Erbitux were up 38% year over year to $167 million in the U.S. for the fourth quarter. We'll get the hard details and statistics from this clinical study at the American Society of Clinical Oncology meeting in June. If the results are positive enough, then ImClone will have another catalyst to help it fend off the competition and continue the strong Erbitux sales growth seen over the past year.

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Fool contributor Brian Lawler does not own shares of any company mentioned in this article. The Fool has a disclosure policy.