Localisation refers to the medical process whereby a lump in the breast tissue is 'located' so that a biopsy can be taken from the tissue in the lump to determine its makeup. 'Excision biopsy' refers to the removal of this tissue for testing. This process is used where it is not possible to feel the lump in the breast tissue and where it is vital that the surgeon knows that the biopsy is taking tissue from the right site.
Localisation is normally performed using a procedure called 'wire localisation'. Wire localisation involves a radiologist pinpointing the exact location of the lump using mammography or ultrasound and then marking the lump with a very fine guide wire that indicates where the lump is for the surgeon. The wire is removed after the biopsy has been taken.
Localisation and excision is different from 'wide local excision' (where a larger area of breast tissue is removed) – wide local excision only takes place where a diagnosis has already been made, whereas a localisation and excision biopsy is only to identify whether breast tissue is cancerous or not.
In practice the localisation part of the procedure takes place before surgery to complete the excision biopsy.