LONDON (Reuters) - Britain’s healthcare watchdog NICE, which assesses the cost-effectiveness of medical treatments, has stopped short of recommending the use by the National Health Service (NHS) of Merck & Co Inc’s immunotherapy drug Keytruda in newly diagnosed lung cancer patients, after giving the go-ahead in December for patients who had prior treatment.

Keytruda is already approved as a cost-effective treatment in melanoma and the National Institute for Health and Care Excellence also on Dec. 2 approved its use in the treatment of lung cancer patients who had started on chemotherapy, after Merck & Co cut the price further for the NHS.

But trial data so far on the survival benefit of Keytruda as an initial lung cancer treatment has not been reliable enough, according to NICE’s draft guidance, which will be subject to public consultation until 21 March.

“The exact size of the overall survival gain for Keytruda compared to the current standard of care was uncertain because of the immaturity of the data,” a NICE spokeswoman said.

Keytruda has proved effective in fighting non-small cell lung cancer in patients with high levels of a protein called PD-L1, which makes them more receptive to immunotherapy.

The average cost of a course of treatment in Britain is around 29,000 pounds ($36,000) at the full list price but the NHS will pay less after getting a confidential discount.

($1 = 0.8042 pounds)