AstraZeneca Won't Present Key Cancer Drug Data at Conference

The biggest medical confab of the year, the American Society of Clinical Oncology annual meeting, starts May 18, but the rumor mill is already buzzing. The latest: AstraZeneca (AZN Quote) has reportedly pulled some key, late-stage data about its cancer drug Iressa from a highly anticipated plenary session on lung cancer scheduled for the ASCO conference.

Wall Street is tracking Iressa's development closely because the cancer drug has blockbuster potential and is similar to ImClone Systems' (IMCL Quote) Erbitux. Now that Erbitux is delayed, Iressa is expected to hit the market first, probably in the second half of this year.

The British pharmaceutical company was expected to take the wraps off results from one, possibly two, phase 3 clinical trials of Iressa. But earlier this week, several sources told TheStreet.com that AstraZeneca pulled the data from the conference. The reason for the withdrawal was not known, but the action could have either positive or negative implications for the drug.

The Food and Drug Administration is already considering Iressa for approval, based on results from earlier trials. AstraZeneca will be discussing these data at ASCO.

Phase 3 Data the Issue

These randomized, controlled phase 3 trials enroll about 2,000 lung cancer patients combined, and test Iressa in combination with existing chemotherapy treatments. Patient accrual into the trials, being conducted in the U.S. and Europe, was completed last April. The clinical endpoint of the studies is patient survival, the gold standard for cancer drug trials. This means that AstraZeneca must show that patients taking Iressa live longer than patients who don't take the drug.

AstraZeneca spokeswoman Mary Lynn Carver confirmed that phase 3 Iressa trial results will not be presented at the ASCO conference simply because data on patients are still being collected and analyzed. While acknowledging that the company tried to have the data ready for ASCO, she would neither confirm nor deny that some data from the trials were actually submitted, then pulled. The company is hopeful that results from these trials will be ready for release sometime this year, she added.

If AstraZeneca is still collecting data from its phase 3 trials almost a year after the last patient was enrolled, that could mean very good things for the drug's efficacy.

Even if the data are not completed but look positive, AstraZeneca could conceivably release some preliminary results suggesting that patients are living longer after taking Iressa. The fact that the company is not doing this has some Wall Street fund managers puzzled and fearful that there are problems with the trial results.

"I'm cautious because of all the rumors, but I tend to think that the lack of phase 3 Iressa data at ASCO is a positive," says Catherine Arnold, pharmaceutical analyst with Sanford Bernstein. "You always like to see a trial with a survival endpoint go as long as possible." Arnold rates AstraZeneca a buy, and her firm doesn't do underwriting.

Already at the FDA

AstraZeneca has already filed for Iressa's approval with the FDA, based on results from two phase 2 studies involving about 420 non-small-cell lung cancer patients. To be eligible for the study, patients must have had already failed existing chemotherapy treatments. They were then given Iressa as a monotherapy to see whether their tumors shrank.

Results from one of these studies, conducted in Europe and Japan, were released last year, showing an impressive 18.7% tumor response rate. AstraZeneca's Carver says results from the other trial, conducted in the U.S., will be released at this year's ASCO meeting.

Oncologists and Wall Street analysts will be looking at these new data closely because they form at least half of Iressa's FDA approval application. Results from the U.S. trial are not expected to be as good as those from the overseas trial because patients treated here were sicker -- failing at least two, sometimes three, courses of chemotherapy before taking Iressa. By contrast, patients in Europe and Japan failed only one, sometimes two, courses of chemo.

There are conflicting opinions on how important the phase 3 Iressa data will be for the ongoing FDA review. AstraZeneca says regulators are satisfied with the phase 2 data, and that efficacy results from the phase 3 trials will not affect the FDA decision. But Bernstein analyst Arnold is not so sure.

"I think the FDA will want to see the efficacy results from the phase 3 trials, at least as supportive data for the application," she says.

Both Iressa and ImClone's Erbitux belong to a new class of experimental drugs that work by blocking a protein called the epidermal growth factor present in large quantities in many cancer cells. When the protein is blocked, cancer cells seem to stop growing or to shrink, leaving healthy cells intact.

There are some important differences between Iressa and Erbitux that make direct comparisons difficult. Iressa is a small-molecule drug, taken in pill form, that works inside of cancer cells; Erbitux is a monoclonal antibody, taken via injection, that interacts with proteins on the outside of cells. Biotech observers are split over which approach will work better, and the drugs haven't been tested enough to provide definitive proof either way. One of Erbitux's strong points is that its most widely reported side effect is an acnelike rash, while Iressa has been associated with diarrhea, in some cases bad enough to interfere with treatment.