Food and Drug Administration staff also said in a review document that the drug, known generically as pazopanib, has a safety profile for patients with soft-tissue sarcoma that is similar to indications for renal cell carcinoma, for which Votrient is already approved.

The document said the significant benefits Votrient produced in "progression-free survival" were consistent in all patient groups studied by researchers.

But FDA staff said there was no clear explanation for why those survival benefits did not translate into better overall survival. The difference could be ascribed to an imbalance in the number of patients who received follow-up anti-cancer therapy, or could suggest that gains in overall survival were limited to patients with higher progression-free survival rates.

Sarcomas are a group of aggressive cancers of connective tissues of the body.

The National Cancer Institute estimates about 11,000 Americans were diagnosed with soft tissue sarcoma in 2011, and about 4,000 of them died from the disease.

So far, analysts see the drug as a modest seller for the British drugmaker, with global sales expectations peaking around $500 million in 2016, according to forecasts from Thomson Reuters Pharma. The drug garnered global sales of about $60 million in 2010.

To convince British health regulators to pay for the drug, Glaxo proposed a clinical trial to compare it to a rival kidney cancer treatment from Pfizer Inc called Sutent, agreeing to sell Votrient to Britain's state-run health service for less money if it proved less effective.

Both Votrient and Sutent are protein kinase inhibitors, a relatively new class of targeted cancer treatment. They work by trying to block the vascular endothelial growth factor (VEGF) receptor to limit new blood vessels that can feed tumors.

Merck & Co Inc is also developing its own treatment for soft tissue sarcoma via a license with tiny biotech company Threshold Pharmaceuticals Inc.

(Reporting by David Morgan; Editing by Gerald E. McCormick and Derek Caney)

• A Permanent Economic Emergency