Ian Paterson is alleged in negligence suits filed by former patients to have performed up to 1,150 "unnecessary, inappropriate or unregulated" operations.
The General Medical Council, which licenses doctors, suspended Paterson's registration in October pending its inquiry.
West Midlands Police, in central England, said Thursday it was opening a criminal inquiry.
Lawyers allege 700 cases involve procedures in which some breast tissue was left behind after a mastectomy. Other patients allege they received invasive breast surgery when a biopsy may have been sufficient.