European regulators detailed their long-awaited guidelines on biosimilar antibody drugs on Friday, paving the way for cheaper copies of multi-billion-dollar medicines used to treat cancer and other serious diseases.

The rules, which have been keenly awaited by drug companies and investors, specified the trials required, which are shorter than for non-generic drugs, and also left open the possibility that different diseases could be addressed by the same antibody.

"Extrapolation of clinical efficacy and safety data to other indications of the reference mAb (monoclonal antibody), not specifically studied during the clinical development of the biosimilar mAb, is possible based on the results of the overall evidence provided from the biosimilarity exercise and with adequate justification," the European Medicines Agency said in a statement published on its website.

However, it said when a reference antibody was licensed in two widely differing diseases, such as in rheumatoid arthritis and in cancer, such extrapolations for a copy antibody would be more "challenging."

The agency also said the drugs could be subject to more thorough monitoring once they were authorized than normal.

"As regards post-authorization follow-up, the concept to be proposed by applicants may have to exceed routine pharmacovigilance, and may have to involve more standardized environments," it said.

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.

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

The guidelines might limit the field to a few well-funded companies such as Teva, Novartis and Hospira, which would be good news for original producers of monoclonal antibodies like Roche and Amgen.