Germany’s biggest Drug makers Bayer Pharmaceuticals Corp. and US Partners Onyx Pharmaceuticals Inc. said that Phase III skin cancer tests of their Nexavar (sorafenib) tablets failed to meet their primary endpoint of improving progression-free survival (PFS).

The addition of the drug Nexavar to chemotherapy failed to improve the survival of skin cancer patients.

“We are disappointed, first and foremost, for the patients with refractory metastatic melanoma for whom treatment options are so limited,” Onyx chief executive Hollings Renton said in a statement.

“However, this trial does not change our commitment to, and belief in, Nexavar. We hope to demonstrate utility in a wide variety of tumors and we will continue to broaden our clinical program, including increasing our attention to the more common malignancies in which anti-angiogenics have demonstrated activity.”

Bayer, which bought Schering AG for 17 billion euros ($22.6 billion) earlier this year to broaden its range of medicines, has said Nexavar may bring in more than $1 billion in annual sales if the drug is approved to treat a range of malignancies. Bayer, based in Leverkusen, Germany, and Onyx are testing the medication on patients with liver and lung cancers.

Shares of Onyx fell $4.75, or 27.1 percent, to $12.75 in pre-market activity on the INET electronic exchange after closing Friday at $17.50 on the NASDAQ. The stock has traded between $12.70 and $30.66 over the past 52 weeks.

The companies plan to continue research of the drug in melanoma. Data from the study will be released at an upcoming medical conference.