What it is and why it matters
Many breast cancers are now picked up on imaging before they can be felt — particularly the small, early cancers detected through screening mammography or as incidental findings on imaging done for another reason. These are called impalpable cancers.
Surgery for an impalpable cancer presents a specific challenge: the surgeon cannot rely on touch to find the lesion in theatre. Instead, the cancer is marked before surgery using one of several localisation techniques, so that the surgeon can find and remove it accurately at the operation.
Localisation has been a routine part of breast cancer surgery for decades. The techniques have evolved — from the long-established wire localisation to newer approaches such as Magseed and LOCalizer, each with its own advantages. The choice depends on the lesion, the hospital’s available equipment, and the patient’s logistical circumstances.
When localisation is needed
Localisation is performed when the lesion to be removed cannot be reliably identified by touch in theatre. The most common situations are:
- Screen-detected breast cancers — small invasive cancers or DCIS found on screening mammography that are not yet palpable.
- Microcalcifications on mammography — clusters of tiny calcium deposits that may represent DCIS or invasive cancer; visible on imaging but not on examination.
- Small lesions seen only on MRI or ultrasound — where the lesion is below the threshold of clinical examination but clearly visible on imaging.
- Marked lesions after biopsy — at the time of needle biopsy, a small clip or marker is often placed in the lesion. If neoadjuvant chemotherapy is given afterwards and the lesion shrinks or disappears on imaging, the position of the original marker is what guides the surgical excision.
- Repeat surgery for a previously biopsied or partially treated lesion where the residual abnormality is no longer easy to find on examination.
Localisation also has a role in lymph node surgery — for example, marking a previously sampled positive lymph node so that it can be specifically retrieved at the time of axillary surgery (sometimes called “targeted axillary dissection”).
The available techniques
Wire localisation
The traditional approach. A fine flexible wire, with a small hooked end, is inserted into the lesion under imaging guidance (mammography or ultrasound) on the morning of the operation. The hook anchors the wire in the lesion; the rest of the wire protrudes through the skin and is taped securely to the chest.
In theatre, the surgeon uses the wire as a guide to locate the lesion and removes it together with a rim of surrounding tissue. The whole specimen — including the wire — is then X-rayed to confirm the lesion has been included.
Advantages: widely available, well-established, low equipment cost.
Disadvantages: the wire must be placed on the same morning as the operation, requiring same-day coordination between the imaging department and the operating theatre. The wire protruding through the skin is awkward; some patients find it stressful. A wire that is dislodged or pulled by clothing in the few hours between insertion and surgery can require re-insertion.
Magnetic seed (Magseed)
A small magnetic seed — about the size of a grain of rice — is implanted into the lesion under imaging guidance using a needle, similar to a biopsy. Unlike a wire, the seed is fully internal: nothing protrudes through the skin.
The seed is placed at any time before the operation — for the original Magseed, up to about 30 days before surgery — which decouples the imaging appointment from the surgical day. LOCalizer is licensed for longer-term placement, which can be useful when localisation is planned before neoadjuvant chemotherapy. In theatre, the surgeon uses a hand-held probe connected to the Sentimag system, which emits a sound when it is close to the seed, so the lesion can be located through the skin without difficulty.
Advantages: placed in advance (much less logistical pressure on the day of surgery); fully internal (no wire to manage between insertion and operation); MR Conditional (safe in 1.5T and 3T scanners) — but produces a local signal void around the seed that obscures the immediate surrounding breast tissue on MRI, so MRI of that breast is generally completed before seed placement rather than between placement and surgery.
Disadvantages: the equipment (Sentimag system, magnetic seeds) is more expensive than wire kits; not yet available in every hospital. Currently used in HCA UK and in 40+ NHS trusts.
LOCalizer (radiofrequency identification tag)
A small radiofrequency identification tag (RFID tag) — similar in concept to a Magseed but using radiofrequency rather than magnetism — is implanted into the lesion under imaging guidance. The surgeon uses a hand-held reader in theatre that detects the tag, similar to the Magseed approach.
Advantages and disadvantages are similar to Magseed: placed in advance, fully internal, requires specific equipment.
Radioactive seed localisation (rare in UK practice)
A tiny seed containing a low-dose radioactive isotope (typically iodine-125) is implanted into the lesion. The surgeon uses a gamma probe in theatre to find the seed. Common in some US centres but rarely used in UK practice because of the regulatory burden of handling radioactive material in routine breast surgery.
Carbon track marking
For some lesions — particularly those marked at biopsy with a clip — a fine line of carbon dye can be tracked from the skin to the clip under imaging guidance. The surgeon follows the dye line in theatre. Less commonly used in UK practice but useful in specific situations.
Choosing between techniques
For most patients, the choice between wire, Magseed, and LOCalizer is made based on:
- What the hospital offers — Magseed and LOCalizer require specific equipment that not all hospitals have.
- The logistical situation — Magseed and similar pre-placed devices are particularly useful when the imaging department and the operating theatre are not in the same building, or when same-day coordination is difficult.
- Patient preference — some patients strongly prefer not to have a wire protruding from the skin.
- The lesion itself — most lesions can be marked equally well with any of the techniques. Some specific situations (very superficial lesions, clips in awkward positions) may favour one over another.
The technique used at your operation is discussed at consultation.
What the experience is like
For wire localisation
- Same morning as surgery: arrive at the imaging department a few hours before the operation.
- Procedure: local anaesthetic to the skin, a small needle through the skin into the lesion under mammography or ultrasound guidance, the wire is passed through the needle, the needle is withdrawn leaving the wire in place. Takes 15–20 minutes.
- Between insertion and surgery: the wire is taped flat to the skin under a dressing. Most patients are comfortable; the wire feels strange but is not painful.
- At surgery: standard general anaesthetic and operation; the wire is removed as part of the specimen.
For Magseed or LOCalizer
- Up to about 30 days before surgery (Magseed) or longer for LOCalizer: a separate appointment in the imaging department.
- Procedure: local anaesthetic, a small needle through the skin into the lesion, the seed/tag is deployed, the needle is withdrawn. Takes 5–15 minutes.
- Between placement and surgery: nothing to manage. The seed sits inside the breast and is not visible from the outside.
- At surgery: standard general anaesthetic and operation; the surgeon uses the detection probe to locate the seed and removes it as part of the specimen.
In all cases, the localised lesion is removed at surgery and the specimen is X-rayed in theatre to confirm the lesion (with its wire/seed/clip) is included. If the X-ray suggests the lesion has not been fully captured, the surgeon takes additional tissue from the appropriate side at the same operation.