ATLANTA - Five days of 90-degree heat gave way to more seasonable temperatures here as the estimated 30,000 attendees began arriving Friday for the annual American Society of Clinical Oncology meeting, held at the Georgia World Congress Center.

In previous years, the conference has highlighted some of biotech's biggest achievers, such as Genentech Inc.'s Herceptin, and Onyx Pharmaceuticals Inc.'s Nexavar, which were featured at last year's meeting in Orlando, Fla. Those two drugs received attention this year, too, but mainly because of news from competing products.

Big pharma firms Pfizer Inc. and GlaxoSmithKline plc, both of which presented promising data over the weekend, are clamoring for a share of the cancer market and threatening to push some of biotech's drugs to the side.

For Emeryville, Calif.-based Onyx, that threat is imminent. In December, Onyx and partner West Haven, Conn.-based Bayer Pharmaceuticals Corp. gained approval for Nexavar (sorafenib) in patients with advanced renal-cell carcinoma, but gained a competitor a month later when Pfizer's Sutent (sunitinib) got the FDA's nod.

Sutent's data have been impressive.

On Sunday, investigators presented results from a Phase III trial of Sutent in 750 patients with advanced kidney cancer who had received no prior treatment, showing that about 25 percent of those receiving Pfizer's orally administered drug saw their tumors shrink, compared to about 5 percent of those receiving interferon injections. Progression-free survival for patients in the Sutent arm averaged 11 months, compared to five months in the interferon group.

Sutent, a multi-tyrosine kinase inhibitor, originally was discovered by Sugen Inc., a Redwood City, Calif.-based firm acquired by Pharmacia Corp. for $650 million in 1999. Three years later, Pharmacia was bought out by Pfizer in a $60 billion deal. (See BioWorld Today, June 16, 1999, and July 16, 2002.)

Shares of Onyx (NASDAQ:ONXX) fell about 15 percent Monday, or $3, to close at $16.82, due partly to the Sutent data and partly to the company's own Phase III data on Nexavar, presented at ASCO on Monday.

Investigators reported that patients with advanced kidney cancer receiving Nexavar tablets demonstrated longer overall survival than placebo patients, but the data weren't good enough for partners Onyx and Bayer to stop the survival analysis early. Overall survival for Nexavar patients averaged 19.3 months vs. 15.9 months for patients in the placebo arm. Data improved to 19.3 months vs. 14.3 months, after investigators made adjustments to account for the placebo patients who had switched over to the Nexavar group when the study was unblinded in April 2005. Since then, about 48 percent of placebo patients crossed over.

The trial is expected to continue to its final analysis, planned at 540 deaths.

Tykerb's Potential In Breast Cancer

While Pfizer generated Sunday's buzz, it was London-based GlaxoSmithKline that had the spotlight on Saturday, presenting pivotal data of Tykerb (lapatinib ditosylate), a small-molecule dual kinase inhibitor, in breast cancer.

The Phase III study tested Tykerb in combination with capecitabine (Xeloda) in 392 women with refractory advanced or metastatic ErbB2-positive breast cancer whose disease had progressed following Herceptin (trastuzumab) treatment or other therapies. Results showed that the addition of Tykerb nearly doubled the time to progression to 36.9 weeks (8.5 months) in the combination group to 19.7 weeks (4.5 months) in the capecitabine-only group.

Data were so positive that GSK stopped enrollment in April, following the independent safety monitoring board's recommendation, because it already met the primary endpoint of time to disease progression. GSK plans to file for FDA approval during the second half of this year.

Orally administered Tykerb is designed to work by inhibiting the tyrosine kinase components of ErbB1 and ErbB2 receptors. If approved, analyst Christopher Raymond, of Chicago-based Robert Baird & Co., said it's unlikely that Tykerb immediately would cut into sales of South San Francisco-based Genentech's Herceptin, which has been the predominant biologic in breast cancer since its 1998 approval.

Aimed initially at becoming an alternative for patients who fail Herceptin therapy, Tykerb is not believed to "impact Herceptin in the near term," Raymond wrote in a research note, though Tykerb's "front-line development program will need to be watched."

Additional data presented at ASCO also suggested Tykerb's ability to decrease the occurrence of central nervous system or brain metastases, which affects about one-third of women with breast cancer due to ErbB2 overexpression.

The interim analysis shows that four patients in the Tykerb-plus-capecitabine arm experienced CNS relapse vs. 11 patients in the capecitabine-only arm.

GSK has an ongoing Phase II study of Tykerb as a monotherapy to prevent brain metastases.

Genentech recently completed the submission of a supplemental biologics license application with the FDA for Herceptin to treat early stage, HER2-positive breast cancer. The product is marketed in Europe by F. Hoffmann-La Roche Ltd., of Basel, Switzerland.

Genentech's stock (NYSE:DNA) lost $2 Monday to close at $80.29.

The conference ends today.