(Adds background on oral MS drug market)

* Merck pulled plug on cladribine in 2011 towards end of Phase III

* Oral MS drugs from Biogen, Novartis with more than $2 bln sales

* Merck says new data, additional analysis prompted move (.)

By Ludwig Burger

FRANKFURT, Sept 11 (Reuters) - Germany's Merck KGaA is to seek approval from Europe's regulators for the use of its cladribine tablet to treat multiple sclerosis, in a fresh attemp to enter a multi-billion dollar market for a drug it had given up on four years ago.

In 2011 U.S. drug regulators' concerns about whether cladribine could cause cancer put an end to Merck's development and marketing plans for the drug.

At the time, it was conducting Phase III trials, which the company says have since yielded new insights.

"The decision follows the company's evaluation of new data and additional analyses of the compound's benefit-risk profile," the company said in a statement.

A spokeswoman declined to comment further on the findings or where the new data came from. Fresh trials were not carried out.

But the move signals confidence that cladribine could hold its own in an oral MS drugs market that has become increasingly crowded since Merck pulled the plug on its project in 2011.

Biogen's Tecfidera, with $2.9 billion in sales last year, looks the strongest contender in the class after it became the third oral MS drug to get to market after Gilenya from Novartis, with $2.5 billion in sales, and Sanofi's Aubagio, with 433 million euros ($489 million) in sales.

All three are taking market share from established injectable MS drugs such as Merck KGaA's Rebif, Teva's Copaxone and Bayer's Betaferon/Betaseron.

Merck said it sent a letter of intent to European healthcare regulators to meet certain requirements before it can submit the official request for approval.

The company is also looking to seek approvals in other markets.

The additional costs of getting approval are limited because Merck has already finished the third and last stage of testing on humans that is required for approval, and which is by far the most expensive phase during the development cycle.

($1 = 0.8857 euros) (Editing by Greg Mahlich)