A half-stake in two Midtown office buildings is being offered by cancer research institutes and could reap over $1 billion towards their endowments.

The Fisher Brothers developed the towers at 1345 Ave. of the Americas and 605 Third Ave. and retain the operating share while entities benefitting cancer centers at Memorial Sloan-Kettering, Harvard Medical School, Johns Hopkins, MIT, Stanford University and the University of Chicago sell their ownership positions.

Office investment gurus Douglas Harmon and Adam Spies of Eastdil Secured have been tapped to sell the stakes, according to Real Estate Alert.

The buildings, which total 3 million square feet, are worth about $2.5 billion, sources said, so the 50 percent interest should sell for roughly $800 a square foot.

The late-billionaire shipping magnate Daniel Ludwig invested with the Fisher Brothers in the 1960s when the two Class A office properties were being developed and under the terms of his estate, in 2006 Ludwig’s foundation set up the cancer centers and gave them the stakes in the buildings.

None of the parties returned requests for comment.

The signature black 50-story tower at 1345 Sixth on the western blockfront between 54th and 55th Streets was developed in 1969 and renovated last in 2004.

The 2 million square-foot Emory Roth & Sons designed building has Citibank as a retail tenant off the wide plaza where signature dandelion-like water fountains spray in nice weather. Alliance Bernstein leases a hefty 1.1 million square feet through 2024 while Allianz and Avon are among its other main office tenants.

The property includes a 341-car garage and the movie premiere palace known around the world — the Ziegfeld Theater — on W. 54th St., which was developed on the western side of the tower specifically for the Walter Reade Theatres on a lease that ends in 2018.

The 1 million square-foot 605 Third Ave., also designed by Emory Roth on the eastern blockfront between East 39th and 40th streets includes a rare, 705-car garage. Known as the Neuberger Berman building for its main tenant of 375,000 square feet, it also hosts the Spanish language broadcaster, Univision, and offices for the nearby United Nations.

Last year, the Eastdil duo sold similar stakes to recapitalize among others the St. John’s Terminal on West Street, 1411 Broadway, 1440 Broadway, 14 Wall St. and 900 Third Ave.

They are completing the sale of the Sony building for $1.1 billion that should close by Monday, and recently placed 650 Madison Ave. on the market for Carlyle Group and Ashkenazy Aquisitions– another tower that should sell for over $1 billion.

EXTRA