GlaxoSmithKline yesterday said it had taken the decision to halt enrollment into a late-stage study of its new breast cancer drug Tykerb (lapatinib) after better than expected results were thrown up by an independent Data and Safety Monitoring Board. It will now definitely seek US and European approval in the second half of the year.

The trial showed that Tykerb plus Roche's Xeloda (capecitabine) was significantly better than Xeloda alone in improving time to disease progression in women with advanced breast cancer who had already failed to respond to other antitumour therapies, including Roche’s blockbuster Herceptin (trastuzumab). GSK had been hoping to demonstrate a 50% improvement on this endpoint and – although the UK giant did not reveal the exact figures – did note that it had "exceeded the primary endpoint."

GSK had originally expected to seek regulatory clearance of the drug – an oral therapy – in the latter half of 2006 or early 2007, according to a company spokeswoman, who said this latest move has given GSK "greater confidence" in filing during the earlier part of the forecast. And it is already expected to clear the all-important $1 billion peak sales mark, say onlookers.

Tykerb is a dual-kinase inhibitor, blocking the ErbB1 (EGFR) and ErbB2 receptors, which are associated with cancer-cell proliferation and tumour growth. In data unveiled at the end of last year, GSK said 40% of breast cancer patients experienced either tumour reduction or stable disease after treatment with the drug for at least 24 weeks.

Three new Phase III trials were initiated by January 2006, two in first-line therapy and one in refractory breast cancer in combination with Herceptin. All in all, seven pivotal studies are ongoing in the breast cancer field, noted the spokeswoman, including one evaluating Bristol-Myers Squibb's Taxol (paclitaxel) plus Roche's Herceptin versus a triple combination hit with Taxol/Herceptin and Tykerb. Data from all the trials are expected to come in over the 2006-09 period, she added, noting that because of a fast-track designation with the US Food and Drug Adminstration, they will be submitted on a rolling basis.

Meanwhile, GSK has signed a potentially multimillion dollar deal with US biotechnology company Sirna, focused on the discovery, development and marketing of RNA interference compounds in the respiratory field. Sirna will receive a $12 million upfront payment, and potentially more than $700 million in milestones.