Commercial real estate developer Forest City Enterprises plans to break ground this fall on a stalled 250,000-square-foot biotechnology office and lab complex at 300 Massachusetts Ave., Cambridge, outside Central Square, after the City Council approved the zoning petition.

The building will be occupied by Millennium Pharmaceuticals, the Japanese-owned cancer drug company, which has about 1,200 employees in Massachusetts and is outgrowing its space in a half-dozen other buildings at Forest City’s University Park development near the proposed site.