NEW YORK -- Suzanne Greco will officially take over as president at Subway as her brother, the co-founder of the sandwich chain, is treated for leukemia.

Greco will oversee day-to-day operations and report to her brother, Fred DeLuca, who will remain CEO, the company said.

Greco, 57, sits on Subway's board and has been involved with the company since it opened its first store in 1965. She had already been overseeing the company's operations and marketing departments.

Subway, which is based in Milford, Connecticut, and has about 44,000 locations around the world, is privately held and doesn't disclose its financial results. Last year, industry tracker Technomic said average sales for Subway stores in the U.S. declined 3 per cent from the previous year.

The company announced in 2013 that DeLuca, 67, had been diagnosed with leukemia. Subway said at the time that its senior management team was handling day-to-day operations, but that DeLuca was communicating regularly with them from Florida.

"Fred is still very active in the company while he continues to focus on his health," a Subway representative said in an email. The company declined to share specifics on DeLuca's health.