A guide block configured to be inserted into an opening of a grid-like breast receiving pressure plate to guide a tissue-removing device to a desired location within a patient's breast. The guide block includes a body having a body length between a proximal face and a distal face. The body length has a plurality of sides configured in a polygonal arrangement that corresponds to a shape of the opening in the grid-like breast receiving pressure plate. Each of a first guide passageway and a second guide passageway extends within the polygonal arrangement. The second guide passageway is coextensive with and configured to overlap the first guide passageway in a direction of extent of the plurality of sides to form a longitudinal opening between the first guide passageway and the second guide passageway that extends from the proximal face to the distal face.
