UPDATE 1-Glaxo boosts cancer research with UK biotech deal

* Oxford BioTherapeutics to get up to $370 mln if drugs work

* Deal covers therapeutic antibodies for treating cancer

(Adds details, background)

LONDON, May 18 (Reuters) - GlaxoSmithKline GSK.L took another step to bolster its early-stage pipeline of cancer drugs on Monday by signing a deal worth up to $370 million with privately held British biotech group Oxford BioTherapeutics.

The strategic alliance covers the discovery and development of new therapeutic antibodies for treating primary, metastatic and recurring forms of cancer, with Glaxo developing drugs against selected targets identified by Oxford BioTherapeutics (OBT).

OBT will also develop one antibody through to clinical proof of concept, at which point Glaxo will have an option to license it.

OBT said it would receive an undisclosed upfront payment and would be eligible for up to a total of $370 million in milestone payments, depending on the success of the new drugs in development. It will also get royalties on any eventual sales.

Reporting by Ben Hirschler; editing by John Stonestreet