The next office building in the tech-heavy Cortex tech district could break ground next quarter, a project that would add 120,000 square feet of office space to one of the region’s hottest employment districts.

Clayton-based Koman Group says it is nearly ready to build on the 3.25 acres of land it purchased two years ago in the Cortex district about four miles west of downtown. The 120,000 square feet of office space is up from 90,000 square feet it had previously marketed on the site at the southwest corner of Sarah Street and Clayton Avenue. Koman declined to name potential tenants.

“We are working with Cortex leadership and neighborhood constituents on the ultimate development plan, including possible integration of residential and mixed-use buildings as well as common area courtyard spaces,” a Koman spokeswoman said in a statement.

Cortex, a redevelopment corporation made up of major institutions including Washington University, St. Louis University and BJC HealthCare, still needs to review the revised development plan before the project proceeds. But Cortex CEO Dennis Lower said the district is close to 98 percent leased and Koman’s project would add “much-needed” space.

“It is in accordance with the master plan and would be an exciting addition of space to the Cortex district,” he said.