City commissioners unanimously approved a special use permit that will allow laboratory space for a cancer research firm to locate downtown.

Commissioners approved the special use permit for the second floor of 647 Mass. without knowing whom the tenant for the building may be.

The building’s ownership group — which is led by executives of the Gene Fritzel Construction Co. — have said they are in discussions with a company that conducts research on cancer drugs. But a lease for the space has not been finalized.

The owners did agree to limit the type of activity that could occur at the site, including prohibiting any known toxins, pathogens or type 1 carcinogens on the site.