Biotech giant Amgen and generic drugmaker Watson Pharmaceuticals said that they will form a collaboration to develop and commercialize several biosimilar oncology antibody drugs. The announcement comes on the heels of a similar deal between Biogen Idec and Samsung.

Under the terms of the agreement, Amgen will assume primary responsibility for developing, manufacturing, and initially selling the biosimilars while Watson will provide its expertise in the commercialization and marketing of generic medicines.

Neither company has specified which drugs they plan to develop but the collaboration will not pursue biosimilars of any of Amgen’s branded products. Speculation, according to a report in The New York Times, is that the companies would pursue their own version’s of Genentech’s cancer drugs Herceptin, Rituxan, and Avastin.

Though the FDA has not yet provided specific clinical development rules for biosimilars, copycat biologics are expected to become a big business worldwide as patents expire on top-selling branded biologics over the coming years.

A growing number of biotechnology companies are aiming to incorporate the potential market as an extension of their own businesses. Just this week, Baxter and Momenta Pharmaceuticals agreed on a biosimilars deal that could net Momenta more than $500 million if it reaches certain milestones.

And, two weeks ago, Biogen Idec closed a similar $300 million deal with Samsung Biologics, a division of Samsung, to develop biosimilar drugs. Burrill & Company, publisher of The Burrill Report, served as an advisor to Samsung on the transaction.

Amgen and Watson will split the costs of development roughly in half, with Watson providing up to $400 million. Watson would receive royalties and milestone payments on any sales of the drugs.

Amgen will initially do most of the development and marketing, but that role will change as the market for biosimilars matures. Eventually, the companies believe that the biosimilar market could become more like the market for conventional generic drugs, with competition focused around price. Should that happen, Watson’s expertise would come into greater play. “Over time, the commercial relationship modifies,” says Paul Bisaro, CEO of Watson. “We both have strengths that make sense for each other no matter how the market develops.”