* AstraZeneca chasing Bristol, Roche and Merck
* Biotech unit MedImmune centre-stage in cancer research
* Broad pipeline offers scope for multiple combinations
By Ben Hirschler
LONDON, Oct 14 (Reuters) - AstraZeneca is betting on drug combinations to help it catch up with industry leaders in the race to develop new treatments that harness the body's immune system to fight cancer.
Bristol-Myers Squibb, Roche and Merck & Co are currently out in front with such immunotherapies, which analysts believe may extend patients' lives significantly and generate tens of billions of dollars in annual sales.
But AstraZeneca argues that the breadth of its portfolio of experimental cancer drugs - including both traditional "small molecule" pills and injectable biologics, made in living cells - puts it in a powerful position when it comes to producing drug cocktails.
Such combinations are expected to be crucial as oncologists seek to block cancer on multiple fronts. The potential for combining immunotherapies was highlighted in May in a study of two Bristol treatments for melanoma.
"We are completely changing the paradigm of how to treat cancer," said Bahija Jallal, head of the biologics arm of AstraZeneca.
"The field is still very open for combinations and I think we are very much in the race."
Although it is behind the three market leaders, Jallal said "very, very few" companies had the opportunity to choose from both small molecule treatments and biologics when designing future drug combinations.
Jallal is in charge of MedImmune - the U.S. biotech business that AstraZeneca bought in 2007 for $15.6 billion.
At the time, the MedImmune purchase was slammed by many investors, who felt that David Brennan, the chief executive at the time, had overpaid for a company with few promising new drugs.
Six years on, however, MedImmune is emerging as a key plank of new CEO Pascal Soriot's bid to reinvent AstraZeneca's drug pipeline, following past disappointments.
Much of the attention is focused on the cancer immunotherapy portfolio.
The drugs may be at an early stage but the breadth of the pipeline is a big plus for AstraZeneca, especially given its historic success in developing cancer drugs such as tamoxifen, Arimidex, Faslodex and Iressa.
What is more, the pace of cancer drug development has accelerated markedly, making it possible for drug companies to catch up fast.
Experimental AstraZeneca drugs with potential for use in combinations include MEDI4376, a PD-L1 drug that helps the immune system fight cancer cells by disabling a protein that acts as a brake on the body's ability to detect them.
AstraZeneca reported promising Phase I clinical trial results with MEDI4376 last month and it is now set to be tested alongside other medicines, such as the established cancer pill Iressa and the experimental antibody drug tremelimumab.
Tremelimumab works in a similar way to Bristol's melanoma drug Yervoy, which impressed oncologists last month when a study showed that some patients with the notoriously deadly disease survived for up to 10 years.
Melanoma has been the initial focus of much immunotherapy work but the field is now widening out to other cancer types.
Citi analysts expect immune system drugs to form the backbone of treatments for up to 60 percent of cancers over the next decade and estimate that they could generate annual sales of $35 billion.