* Aims to be a leader in MS, seeks acquisitions

* Genzyme confident in Lemtrada US approval in Q4

* Unveils more long-term efficacy and safety data

By Natalie Huet

PARIS, Sept 11 (Reuters) - Sanofi rare disease unit Genzyme hopes to become a leader in the multiple sclerosis (MS) field with the help of new products developed in-house but also through acquisitions, senior Genzyme executives told Reuters.

The Cambridge, Massachusetts company is confident in the commercial success of its two MS drugs Lemtrada and Aubagio and is "very active" in its hunt for external growth, Bill Sibold, the head of Genzyme's MS franchise, told Reuters.

He declined to comment on potential targets but said Genzyme was looking to snap up truly innovative products, was regularly talking to other companies and constantly weighing its options.

Asked if Genzyme had a budget for acquisitions or if "the sky's the limit", Sibold laughed and simply replied that it helped to be a part of Sanofi - a group with deep pockets: "If the opportunity is the right opportunity, we'll evaluate it... We're well resourced to execute our strategy."

Pricing pressures from cash-strapped governments seeking to restrict healthcare spending and tough competition from generics have prompted drugmakers worldwide to reshuffle their businesses and triggered a wave of mergers and acquisitions.

Sanofi bought Genzyme, a U.S. biotech firm, for $20.1 billion in 2011 as part of a broader revamp of its drug portfolio. The unit posted a 25 percent jump in sales in the first half of the year, and is one of the core emerging businesses Sanofi is betting on to shake off the impact of patent losses on older drugs such as its blood thinner Plavix.

At the heart of the Genzyme takeover stood its injectable drug Lemtrada, designed to treat relapsing remitting multiple sclerosis, the most common form of the disease, in a market dominated by rivals Biogen Idec, Novartis and Teva Pharmaceutical Industries.

Lemtrada is already sold in Europe but has yet to be approved in the United States, where experts have raised questions about its safety and the quality of clinical studies.

Analysts slashed their sales forecasts for the drug after the U.S. Food and Drug administration rejected Lemtrada's application last December. Sanofi resubmitted an application earlier this year and expects FDA action in the fourth quarter.

"I'm confident in the U.S. approval and I'm confident in how the product will perform and be utilised... The efficacy is just too good," said Mike Panzara, therapeutic area head for Genzyme's MS and neurology program.

POTENTIAL BLOCKBUSTERS

Multiple sclerosis is a chronic, autoimmune condition which affects more than 2 million people worldwide and up to 500,000 in the U.S. It attacks the central nervous system and can cause muscle weakness, pain and cognitive difficulties.

Lemtrada is given in two courses via an intravenous drip and is designed to reprogramme the immune system, but in so doing can make the body more vulnerable to other diseases.

The market is increasingly moving away from injectable treatments in favour of pills such as Novartis' Gilenya and Biogen Idec's Tecfidera, but Genzyme is hopeful Lemtrada's ability to durably reduce the risk of relapse of the disease will win it a slice of the market.

Genzyme is presenting this week before the European Committee for Research and Treatment in Multiple Sclerosis (ECTRIMS) a raft of clinical data for Lemtrada, which Panzara said supports the drug's favourable benefit-risk profile.

"The risks are those that we previously described... But without an increase in risk the longer you follow the patient," he said, stressing that 30 countries had already approved the drug and that it had support from patients and physicians alike.

The ECTRIMS annual meeting will also feature new data on Aubagio, an oral treatment already approved in the U.S and Europe and for which analysts are much more upbeat.

Analysts on average expect Aubagio to hit peak sales of $1.2 billion by 2018, compared with $437 million for Lemtrada, according to forecasts compiled by Thomson Reuters Cortellis.

Sibold declined to comment on the forecasts, but noted that analysts had been pleasantly surprised by Aubagio, and suggested they may also now be underestimating Lemtrada.

"We think that the potential of both products, Lemtrada and Aubagio, is really enormous. Each of them can be a blockbuster," he said.

(Editing by Susan Thomas)