Germany’s Bayer and development partner Onyx Pharmaceuticals of the USA have been rocked by clinical data from a Phase III trial which reveals that their potential blockbuster cancer drug Nexavar (sorafenib) was not effective in treating patients with advanced melanoma.

The PRISM study of 270 patients showed that Nexavar, which is approved for the treatment of advanced kidney cancer, in combination with the chemotherapy drugs carboplatin and paclitaxel in patients with advanced melanoma did not meet its primary endpoint of improving progression-free survival, that is the period when a patient experiences no meaningful tumour growth.

In terms of share price, it was Onyx that suffered most dramatically, with its stock falling almost 30% to $12.25. Chief executive Hollings Renton noted: “We are disappointed, first and foremost, for the patients with refractory metastatic melanoma for whom treatment options are so limited,” but “this trial does not change our commitment to, and belief in, Nexavar.”

He went on: “We hope to demonstrate utility in a wide variety of tumours and we will continue to broaden our clinical programme, including increasing our attention to the more common malignancies in which anti-angiogenics have demonstrated activity.”

There is also no doubting the damage the news has had on Bayer, which has much riding on the success of Nexavar, although its share price was not hurt. Speaking at the company’s autumn press conference in Leverkusen, Germany, only last week, chairman Werner Wenning said sales of the drug should hit the 100 million euro mark for the full year, “yet we have nowhere near exhausted the potential of Nexavar.”

Bayer still hopeful

At a conference call for analysts and investors, Arthur Higgins, chairman of Bayer HealthCare, said “we are clearly disappointed we do not have better news,” but also noted that melanoma is “a particularly challenging and notoriously difficult disease to treat."

Nevertheless, he confirmed that there are two other Nexavar trails currently underway in melanoma (though it was clear from the conference call that enrollment is very slow) and, in addition, the drug is being evaluated as a single agent in a Phase III trial for liver cancer, a study that has completed enrollment.

Also, a Phase III trial of Nexavar combined with carboplatin and paclitaxel in non-small cell lung cancer for treatment-naive patients was initiated in the first half of 2006, and Phase II studies in breast cancer are also planned for the start of next year.