LONDON (Reuters) - Japan's Astellas is seeking more deals to refill its drug pipeline as the pharmaceutical company created through a merger 10 years ago explores opportunities in both established and new therapy areas.

"We're never satisfied with what we have, so we are looking at strategies to augment the portfolio. Nothing is off the table for us," Sef Kurstjens, head of global development at Japan's second-biggest drugmaker, told Reuters.

Last week, Astellas agreed to pay $300 million upfront to access experimental anti-allergy vaccines being developed by privately held U.S. biotech company Immunomic Therapeutics, boosting its position in immunology.

Immunomic's DNA vaccines are still a long way from reaching the market and Kurstjens said such early-stage deals were more likely than ones for late products, where prices have been driven up by a three-year boom in biotech valuations.

"I have to say in recent times the cost of later-stage deals has been phenomenal, so we've placed a lot of bets on the earlier side of the portfolio because we have a fairly full late pipeline," he said in an interview on Wednesday.

Astellas, like other Japanese drugmakers, has so far adopted a low profile amid a record-breaking global wave of drug industry deal-making. Its last really big deal was the $4 billion acquisition of OSI Pharma in 2010, giving it the blockbuster lung cancer drug Tarceva.

The group faces challenges ahead, with patent expiries looming on bladder drug Vesicare and Tarceva in 2018 and 2019.

But Kurstjens said he had high hopes for expanded use of established prostate cancer drug Xtandi, as well as new experimental products for cancer, bladder problems and other conditions. Astellas is also moving into the new areas of muscle diseases and ophthalmology.

Another key focus for investors is progress with a novel pill for anaemia, currently in final-stage trials, which boosts red blood cells by mimicking the body's response to high altitude. If successful, roxadustat could replace injectable EPO products that generate billions of dollars of sales.

Astellas has rights to the drug in Japan and Europe, having licensed it from Fibrogen in 2006, while AstraZeneca has rights in the United States, China and certain other markets.

GlaxoSmithKline also has a similar so-called HIF-PH inhibitor drug at a slightly earlier stage of development.

(Editing by Keith Weir)