European regulators are expected to adopt a conservative stance this week when they set rules for allowing copies of antibody drugs, used to fight cancer, rheumatoid arthritis and other serious diseases.

The new guidelines from the European Medicines Agency (EMA) will open up a multibillion-dollar market to cheaper rivals, but the key question is how difficult - and hence expensive - it will be to win approval for so-called biosimilars.

Industry experts expect a cautious approach, requiring separate clinical trials for different diseases addressed by the same antibody. That would be good news for original producers of monoclonal antibodies, like Roche and Amgen.

For makers of generic drugs, it would push up costs and may limit the field to a few sophisticated and well-funded companies like Teva, which is working on biosimilars with Lonza ; Novartis unit Sandoz; and Hospira.

Lincoln Tsang, a partner at London law firm Arnold & Porter and a former head of biotechnology at Britain's regulatory authority, expects the EMA to play it safe by requiring extensive testing.

"My hunch is that they will be cautious in saying that if you can establish clinical efficacy and safety of a given product for a given indication you can't readily seek approval for another indication," he said. "Given it is such a big therapeutic area, I think they will not like to be seen to be too generous."

Drawing up rules for copies of biotech drugs like antibodies is tricky because they are complex molecules grown in living cells that cannot be made absolutely identical to the original.

The agency's Committee for Medicinal Products for Human Use (CHMP) will decide this week whether to adopt the new guidelines, although it may be another two or three weeks before they are actually published, an EMA spokeswoman said.

There will then be several months of external consultation before the guidelines are formally adopted.

Roche Drug Is Test Case
The first antibody likely to be copied in Europe is Roche's Rituxan, or MabThera, which loses patent protection in 2014. Teva is already running separate clinical trials for its biosimilar version in the drug's two main uses - non-Hodgkin's lymphoma and rheumatoid arthritis - showing it is not banking on simple extrapolation of approval from one disease to another.

"Teva has started clinical trials for each indication. They are cautious. They are conservative," said Lonza spokesman Dominik Werner. "At the moment we expect that a Phase I (trial) will be required and also a Phase III. The key question is whether a Phase II is also needed. We expect (R&D) costs of $100 million per antibody.

If a Phase II is also be needed, we are talking about an additional $20 million, depending on the antibody."

Up to now, complex biotech medicines have been generally immune from generic competition, unlike conventional pills and capsules. That is starting to change as patents expire and regulators work on ways to allow safe and effective copies.

Europe has so far approved 13 biosimilars and the EMA already has six sets of guidelines on simpler biosimilar drugs, including human growth hormone and anemia treatment EPO.

Monoclonal antibodies, however, are the biggest commercial prize, since these treatments are expected to dominate many areas of medicine in the years ahead.

Worldwide sales of all biologic drugs reached some $130 billion in 2009, according IMS Health, and industry analysts believe the potential market for biosimilars could be worth tens of billions of dollars by the second half of the decade.