A device for localizing a target tissue mass in a body includes a tubular trocar portion having a distal end and a proximal end portion that is removably attachable to a handle portion. The trocar portion contains at least a first plurality of locator wires that are movable between a retracted position within the trocar and a deployed position extending radially from the trocar. In a preferred embodiment, the trocar portion has an electrosurgical cutting element at its distal end, and first and second pluralities of locator wires that, when deployed, respectively define first and second locating perimeters. The first plurality of locator wires is connected to a first wire carrying member longitudinally mounted for axial movement within the trocar portion between a proximal position corresponding to the retracted position of the first plurality of locator wires, and a distal position corresponding to the deployed position of the first plurality of locator wires. The second plurality of locator wires is connected to a second wire-carrying member longitudinally mounted in the trocar portion, coaxially with the first tubular member, for movement between a distal position corresponding to the retracted position of the second plurality of locator wires, and a proximal position corresponding to the deployed position of the second plurality of locator wires. The trocar portion has an intermediate portion having first and second pluralities of slot-shaped apertures through which the first and second pluralities of locator wires emerge when moved to their respective deployed positions. With the locator wires in their retracted position, the trocar is passed through a target tissue mass until the intermediate portion is within the mass. The locator wires are then deployed within the mass to anchor the trocar therein and to mark the site for a surgical procedure. In the preferred embodiment, the locator wires are electrically energized to facilitate their deployment electrosurgically.