French cancer immunotherapy specialist OSE Pharma prepares IPO

* Seeking funding for Texopi late-stage trials

* Aims to launch IPO by year-end

PARIS, Sept 18 (Reuters) - French cancer immunotherapy specialist OSE Pharma has registered with market regulator AMF for an initial public offering (IPO) aimed at financing late-stage trials of its Texopi drug for the most common form of lung cancer, the company said on Thursday.

Joining a string of European biotech businesses to consider a stock market listing this year, OSE Pharma is aiming to emulate the success of allergy drug company Circassia, which raised 200 million pounds ($327 million) with its March flotation.

Texopi has already been tested in a Phase II study in patients with non-small cell lung cancer and is set to undergo Phase III trials in the second half of next year, at an estimated cost of 20 million euros ($25.8 million) based on industry standards.

OSE Pharma, which aims to launch the proposed IPO before the end of this year, develops immunotherapy products that fight invasive late-stage cancers by educating the body's immune system to attack tumour cells.

Its injectable treatments are designed to halt the progress of cancer and extend the lives of patients when first-line treatments such as chemotherapy have failed to control the disease.

Boosting the body's immune system to fight tumours is a hot area for drug research, dominated by Big Pharma names such as Bristol-Myers Squibb, Roche and Merck & Co . Analysts estimate the market to be worth tens of billions of dollars in annual sales.

The Phase II study of Texopi showed a one-year survival rate of 59 percent, compared with only 33 percent for patients taking existing second-line treatments.

Texopi has been granted "orphan drug" status in the United States, which means it will receive seven years of market exclusivity if approved.

Lung cancer is generally not diagnosed in patients until it has reached an advanced stage and kills about 1.6 million people each year, according to the World Health Organisation.

OSE Pharma estimates that the global market for Texopi in lung cancer could reach 2 billion euros.

The company also aims to develop the drug for ovarian, colon or breast cancer. It has yet to decide which of those applications to focus on first but plans to begin a Phase II trial by the end of the year. ($1= 0.7767 euro) (1 US dollar = 0.6123 British pound)

(Reporting by Natalie Huet; Editing by David Goodman)