Roche said patients with an aggressive type of breast cancer lived longer after taking its experimental "armed antibody" drug without the disease worsening than those on a mix of GlaxoSmithKline drug Tykerb and Roche's Xeloda.
The positive results from the first Phase III trial of the medicine - dubbed T-DM1 - clears the way for it to be submitted to European and U.S. authorities for approval this year, boosting prospects for a key asset in the Swiss firm's pipeline.
WestLB analyst Oliver Kaemmerer, who sees peak sales potential for T-DM1 of around 1 billion Swiss francs ($1.1 billion), said the latest news was clearly positive but it remained to be seen what the overall magnitude of the benefit was in the study.
In a brief statement on Friday, Roche revealed only that patients on T-DM1 lived "significantly longer" without their disease progressing.
Roche has been developing T-DM1 as a successor to its blockbuster Herceptin, which is expected to generate sales of around $6 billion this year.
A key advantage of T-DM1 over conventional treatment of Herceptin plus chemotherapy is the fact that it causes fewer adverse side effects like hair loss and low white blood cell counts.
T-DM1 combines trastuzumab, an antibody and the active ingredient in Herceptin, with the agent DM1 - a derivative of a powerful type of chemotherapy called maytansine - which is carried directly into cells.
The Swiss company licensed certain technology for the new drug from U.S. biotech firm ImmunoGen, shares in which jumped 10 percent in early trade on Nasdaq on news of the positive clinical trial results.
As well as having fewer unpleasant side effects, Roche believes its new drug offers greater convenience, since it is one drug and eliminates the need to administer chemotherapy.
Analyst hopes for T-DM1 have been running high, following earlier good results in Phase II tests, and a filing of the product with regulators this year had been widely expected on the back of data from the so-called EMILIA clinical trial.
Roche said the EMILIA progression-free survival data would be presented at an upcoming medical meeting, adding that final results for overall survival were not yet mature.
Kaemmerer of WestLB believes the full set of results for progression-free survival are likely to be presented at the June 1-5 annual meeting of the American Society of Clinical Oncology, with overall survival results becoming available by 2014.
Commercially, T-DM1 should help protect Roche's breast cancer franchise, since Herceptin could be exposed to so-called "biosimilar" generic competition in Europe from around 2015.
It also keeps Roche in the breast cancer innovation race in the face of newer medicines that aim to rival Herceptin, like GSK's Tykerb.
Analyst Mark Clark at Deutsche Bank said the positive trial result for T-DM1 further dimmed prospects for Tykerb, sales of which totaled a modest 231 million pounds ($368 million) in 2011.