PARIS, Sept 12 (Reuters) - Sanofi's chief executive said that its key drug dupilumab could possibly be used to treat nasal polyps as well as eczema and asthma.

The FDA approved the injectable antibody drug, developed in partnership with Regeneron, for atopic dermatitis - also known as eczema - in March. It is sold as Dupixent.

The French company plans to submit an application to the U.S. Food and Drug Administration for its use to treat asthma by the end of the year.

Speaking at a Morgan Stanley Conference in New York on Tuesday, Olivier Brandicourt said patients suffering from eczema often also suffered from severe asthma or nasal polyps -- swellings of the nasal lining.

Asked if nasal polyps would be dupilumab's next use, Brandicourt replied: "We are in phase 3 (trials) so it is difficult to give you any insight there but, clearly, (nasal polyps) is one of those comorbidities."

Shares of Regeneron and Sanofi slid on Monday after late-stage trial data for dupilumab in asthma fell short of investor expectations. Analysts said the data appeared less impressive than the drug's mid-stage data.

Investors had also shown disappointment with the sales takeup of Dupixent when Sanofi published its second quarter-results on July 31 but Brandicourt said on Tuesday he was confident the drug would sell well.

(Reporting by Matthias Blamont; Editing by Keith Weir)