(Corrects typo in headline to read 'AstraZeneca' and not 'AztraZeneca')
By Deena Beasley
CHICAGO, June 3 (Reuters) - AstraZeneca Plc, in the headlines for spurning buyout offers from Pfizer Inc, aims to regain prominence in oncology with compelling trial results and a splashy exhibit booth at the world's largest meeting of cancer doctors.
The company is seen as No. 4 in a race to develop the first drug in a new class that fights cancer by unleashing the body's immune system, behind rivals Roche, Merck & Co and Bristol-Myers Squibb.
In a presentation during the American Society of Clinical Oncology meeting in Chicago, Chief Executive Officer Pascal Soriot said AstraZeneca was progressing faster than he had expected with its cancer drug pipeline - an asset that figured prominently in its decision to rebuff Pfizer.
"We remain resolute in our ambition to bring these next-generation cancer medicines to patients as fast as possible," Soriot said in an investor presentation late on Monday.
Wall Street analysts said data at the ASCO conference, which started on Friday and will end on Tuesday, provided evidence that AstraZeneca has made progress. A 2 percent rise in the company's London-listed shares since the meeting began suggests no major disappointments.
"This is more like confirmation than anything revolutionary," said Les Funtleyder, a consulting partner with U.K.-based Bluecloud Healthcare consulting firm.
Pfizer walked away from a takeover bid on May 26. The U.S. drugmaker can be invited back to talks by AstraZeneca, Britain's second-largest pharmaceuticals company, in three months or make a fresh approach on its own in six months under UK rules.
AstraZeneca became known in recent years more for cholesterol drug Crestor and ulcer pill Nexium, which are both due to lose patent protection soon.
The company, which seeks a return to a leading role in oncology, broke new ground decades ago by developing tamoxifen and other hormonal therapies that are still widely used to treat breast cancer and prostate cancer.
AstraZeneca also developed one of the first "targeted" cancer drugs, Iressa. It was pulled from the U.S. market after a large clinical trial showed no survival benefit in lung cancer.
The company's prominent front-row exhibit booth at the ASCO meeting had an airy space-age feel with videos on monitors describing its experimental drugs. Long lines formed for free fruit smoothies.
"It's a bigger booth than AstraZeneca has had in the past," said Briggs Morrison, the company's chief medical officer. "Our intent is to make people know how serious we are."
In all, AstraZeneca presented data from over 40 scientific abstracts for experimental cancer drugs. It said that one of its most closely watched therapies, MEDI4736, may be safer than some rivals, allowing it to be used at higher doses in combination with other drugs. AstraZeneca acquired the drug in its 2007 takeover of U.S.-based MedImmune.
A study funded by the National Cancer Institute showed a combination of two AstraZeneca drugs - olaparib, which blocks a cell-repair enzyme known as PARP, and cediranib, which prevents formation of blood vessels needed by tumors - extended the length of time that ovarian cancer patients lived without getting worse.
Both drugs had been effectively shelved by AstraZeneca after initial clinical trials produced underwhelming results.
"If that happened today, we would never have walked away," said Bahija Jallal, AstraZeneca's executive vice president, global medicines development. "The culture today is to follow the science."
Leerink analyst Seamus Fernandez called the ovarian cancer data the biggest upside surprise at the conference, noting that the drug combination might eventually replace chemotherapy, which would double olaparib's potential sales.
MEDI4736 is part of a closely watched class of drugs known as anti-PD-L1 therapies, which block a tumor's ability to evade the immune system's defenses. A small study in lung cancer patients who tested positive for PD-L1, presented on Tuesday, showed that 39 percent responded to MEDI4736.
AstraZeneca expects that more data looking at a combination of MEDI4736 and tremelimumab in lung cancer will be presented in September at the annual meeting of the European Society for Medical Oncology.
Investors are eager to see whether those results improve upon disappointing lung cancer data from Bristol-Myers, whose combination of melanoma treatment Yervoy and PD-L1 drug nivolumab produced lower-than-expected response rates and a high rate of side effects. (Additional reporting by Bill Berkrot; Editing by Michele Gershberg and Jan Paschal)