UPDATE 1-Sanofi, Regeneron start Phase III cancer trials

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LONDON Aug 23 (Reuters) - France's Sanofi-Aventis SA (SASY.PA) and its U.S. biotech partner Regeneron Pharmaceuticals Inc (REGN.O) have started two Phase III clinical trials on their experimental drug aflibercept for prostate and lung cancer.

Regeneron said in a statement on Thursday that the product, also known as VEGF Trap, would be tested in combination with standard chemotherapy regimens.

Sanofi plans to give a full update on the development programme planned for aflibercept at its R&D day in Paris on September 17.

Discovered by Regeneron, VEGF Trap is a soluble protein given by injection that blocks the formation of an abnormal blood vessel.

Vascular endothelial growth factor, or VEGF, is a protein that triggers the formation of new blood vessels -- a function also known as angiogenesis.

Anti-angiogenesis is a hot area of cancer drug research, with many companies competing to develop products. Avastin, from Genentech Inc DNA.N and Roche Holding AG (ROG.VX), currently dominates the field.