LONDON (Reuters) - Roche’s immunotherapy drug Tecentriq has lost market share to Merck & Co’s rival Keytruda since a clinical trial showed the Swiss company’s medicine failed to improve overall survival in bladder cancer.

FILE PHOTO: The logo of world's biggest maker of cancer drugs Roche is seen at their headquarters before a news conference in Basel, Switzerland February 1, 2017. REUTERS/Ruben Sprich

Many modern cancer drugs are approved on the basis of alternative clinical endpoints, such as tumor shrinkage or reduced risk of disease progression, but extending patients’ lives remains the most important benchmark for oncologists.

Latest data show Tecentriq’s share of the bladder cancer market has slipped to 32 percent from around 45 percent before May’s surprise clinical trial failure, according to an analysis on Thursday by Barclays analysts.

Tecentriq was given fast-track U.S. approval in 2016 based on positive preliminary bladder results - securing it a dominant position - but its overall survival miss contrasted with later success for Keytruda.

Merck’s drug has seen its market share in bladder cancer rise to 16 percent since the Roche setback.

Roche said in a statement that demonstrating an overall survival advantage remained the most clinically meaningful endpoint in cancer.

“However, we believe that the totality of data and other key clinical endpoints should also be taken into consideration with regards to demonstrating a clinical benefit with cancer immunotherapy, such as duration of response, overall response rates and the safety profile, all of which also represent meaningful endpoints for patients and physicians,” it added.

Approving promising new cancer drugs based on such alternative measures means they can get to patients faster, but the issue has sparked debate among medical experts.

According to research published in the British Medical Journal on Thursday, the majority of new cancer drugs approved in recent years in Europe failed to show clear evidence that they improved patients’ survival or quality of life.

The study by researchers from King’s College London and the London School of Economics and Political Science was based on an analysis of cancer drugs authorized by the European Medicines Agency (MEA) from 2009 to 2013.

The study authors expressed concern at the finding. But Winette van der Graaf, professor of personalized oncology at the Institute of Cancer Research in London, said she applauded the increased flexibility shown by the EMA.

“If we want to speed up access for patients to the latest, most innovative new treatments, it’s essential that regulatory bodies... are willing to look at data other than just overall survival,” she said.