* Immuno-oncology moving beyond metastatic cancer
* Shift promises to expand market for blockbuster medicines
* Astra, Bristol trials show drugs work in earlier disease
MADRID, Sept 11 (Reuters) - Cancer doctors are widening the net for immunotherapy, a hot new class of drugs that enlist the body's defences in the fight against tumours.
The latest research shared with 23,000 experts at Europe's top oncology meeting shows how medicines that have already delivered durable benefits in metastatic disease can also work well at an earlier stage.
The findings promise to expand the market for established immuno-oncology (I-O) drugs from companies like Merck, Bristol-Myers Squibb and Roche, while opening up a window for relative latecomers such as AstraZeneca.
AstraZeneca stole much of the limelight at the European Society for Medical Oncology (ESMO) congress in Madrid after clinical trial results showed its I-O drug Imfinzi helped lung cancer patients with mid-stage disease.
Bristol-Myers, meanwhile, proved that Opdivo, which is already used widely in advanced cancer, can prevent relapses in melanoma patients if given straight after surgery. This earlier setting is known as adjuvant therapy.
The data on both drugs highlight how so-called PD-1 and PD-L1 drugs are moving down the treatment curve to earlier-stage disease.
"The aim is to help more and more patients in earlier phases of the disease, like in adjuvant therapy," ESMO President Fortunato Ciardiello told Reuters.
"I think this will be a trend that will increase over the next few years, though we have to cautious because we have to do the proper clinical trials to prove this in each case."
I-O drugs are now being investigated in the adjuvant setting in a range of cancers, including lung, kidney and bladder - and some trials are even underway in the neoadjuvant or pre-surgery setting in the case of breast and head and neck cancers.
By taking the brakes off the immune system and allowing the body's natural killer cells to home in on tumours, immunotherapy offers a different approach to toxic chemotherapy, which causes collateral damage to healthy tissue.
It is not without side effects, some of which can be serious, but it is generally a kinder option - especially when PD-1 and PD-L1 drugs are given on their own.
"There is now a potential to use immunotherapy to change the course of early disease. I think that is one of the most important pieces of news for patients at this ESMO meeting," said Fouad Namouni, Bristol-Myers's head of medical oncology development.
By giving immunotherapy earlier, when immune systems are healthier, the hope is that more patients will be lifted into long-term remission.
"Earlier treatment does seem to produce higher responses, although I'm not sure that is going to be true all of the time," said Roy Baynes, who heads clinical development at Merck.
Some analysts forecast potential sales of immunotherapy drugs at as much as $50 billion a year. However, significant challenges remain, including deciding which patients will benefit most from infused medicines with typical list prices of near $150,000 a year.
The possibility of early intervention also raises questions about screening to spot cancer early on - something that becomes more relevant once potentially curative options are available.
AstraZeneca's chief executive, Pascal Soriot, who expects multibillion-dollar sales of Imfinzi in non-metastatic stage III lung cancer, is hopeful screening will pick up in future.
"If you have a good early treatment then the incentive for screening is massive," he said in an interview. (Reporting by Ben Hirschler#; Editing by Greg Mahlich)