ZURICH (Reuters) - Novartis's investigational drug PKC 412 won U.S. Food and Drug Administration priority review, the Swiss drugmaker said on Monday, keeping up momentum after the prospective treatment for a fast-growing form of leukemia garnered breakthrough therapy status this year.

The FDA's fast-track designation reduces the review to six months for the medicine, also known as midostaurin, being tested against newly diagnosed FLT3-mutated acute myeloid leukemia (AML) and advanced systemic mastocytosis.

Analysts think the drug if approved could generate peak annual sales in the hundreds of millions of dollars by 2020.

Novartis is counting on new medicines including midostaurin to help offset the expiration of patents on drugs including top-seller Gleevec, which is now facing increased generic competition.

Novartis said approval of midostaurin would offer the first new strategy to treat AML in a quarter century.

"FLT3-mutated AML and advanced SM are devastating and rare diseases, with significant unmet needs due to limited existing treatment options," said Bruno Strigini, head of Novartis Oncology, in Monday's statement.

"This regulatory designation signifies the importance of midostaurin as a potential therapy for these patients who haven't had the benefit of targeted medicines."

(Reporting by John Miller; Editing by Michael Shields)