Onyx Pharmaceuticals Inc. (ONXX) and marketing partner Bayer AG (BAYRY) hope to continue expanding sales of kidney and liver cancer treatment Nexavar into a broadly used treatment. Sales growth has been steady since its 2005 U.S. approval and the drug continues to launch in new countries.

THE DRUG: Nexavar is a pill that is usually taken twice a day. It works by blocking multiple signals within cancer cells to discourage the diseased cells from proliferating. It also inhibits blood-vessel growth, which is necessary for tumor growth.

THE DISEASE: Onyx estimates that liver cancer is the biggest growth opportunity for Nexavar because more than 600,000 people worldwide are diagnosed with the disease every year. More than half of those cases occur in China, where Nexavar was approved last summer.

The American Cancer Society estimates that about 23,000 people in the U.S. will get liver cancer in 2009.

The group estimates that about 58,000 Americans will be diagnosed with kidney cancer this year.

THE COMPETITION: Nexavar stands alone as the only targeted therapy to treat advanced liver cancer and Robert Baird & Co recently projected that competition wouldn't emerge for two years at the soonest.

Conversely, kidney cancer is a more crowded market, including Pfizer Inc's (PFE) Sutent and Wyeth's (WYE) Torisel. Newer entrants include Roche Holding AG's (RHHBY) Avastin and Novartis AG's (NVS) Afinitor.

THE SALES: Nexavar had global sales of $678 million in 2008 and profits are split by Onyx and Bayer. Onyx projects 2009 sales rising to a range of $850 million to $875 million.

Nexavar costs about $100 per tablet, which comes to about $6,000 for a month of therapy. Like other drug makers, Onyx offers help to those who cannot pay for treatment and about 70% of commercial patients pay $50 or less a month for the drug.

THE OPPORTUNITY: In July, the companies reported positive results from a mid-stage study of Nexavar in advanced breast cancer when used with a chemotherapy regimen. The full data will be released in coming months, but the news increased hope of success in other cancer types and the possibility of off-label usage.

Nexavar is likely protected from generic competition in the U.S. for quite a while, with patent protection until at least 2020. The drug is currently involved in more than 300 clinical trials, according to clinicaltrials.gov.

THE CHALLENGE: Although Nexavar is broadly studied, cancer trials carry a significant amount of risk even when early data is promising. The drug has failed in late-stage trials in both advanced melanoma and small-cell lung cancer.

In May, the Nexavar partnership showed the first signs of strain after Onyx sued Bayer, alleging the German company secretly developed a successor to Nexavar that may be more effective and dosed less frequently.

WHAT ONYX SAYS: "As we look at the vision of Nexavar, we are looking for all the places in which Nexavar might add benefit, whether in monotherapy or in combination with other therapies."

-Laura Brege, executive vice president and chief operating officer, August 12.

WHAT WALL STREET SAYS: "We are encouraged by the apparent strong signal from a Phase II trial in breast cancer and believe this could potentially add a future growth opportunity. However, the competitive landscape remains unclear."

-Howard Liang, Leerink Swann analyst on Aug. 5

WHAT'S NEXT: Investors will be watching to see the details of the breast cancer data, to be presented at a medical meeting in coming months, in order to gauge its effectiveness and market opportunity compared to competition.

Results from a second mid-stage trial in breast cancer, showing its use in newly diagnosed patients, are expected before year-end.

(This column is a periodic snapshot of the market performance of selected drugs and vaccines.)

-By Thomas Gryta, Dow Jones Newswires; 212-416-2169; thomas.gryta@dowjones.com