How to guide the surgeon to a lesion that cannot be felt under the fingers: hookwire (wire localisation) or magnetic seed (Magseed, Localizer, Sirius). A technical step that has become a pivot of modern breast surgery.
Author & medical review: Dr Jérémie Zeitoun, breast cancer surgeon & gynaecologist — RPPS 10101463296 — trained at Institut Gustave Roussy, Institut Curie and Centre François Baclesse. See full background →
Last updated: · Sources: French SENORIF 2025-2026, SFSPM, HAS, Magseed / Localizer literature. References at the bottom of the page.
The vast majority of breast lesions diagnosed today — early cancers, atypical hyperplasia, papillomas, microcalcifications — are non-palpable. They cannot be felt on clinical examination, are invisible on the skin surface, and cannot be seen with the naked eye once the skin is incised. They exist only on imaging: a 7 mm ultrasound nodule, a focus of microcalcifications on a mammogram, a suspicious MRI enhancement.
When these lesions must be surgically removed, a concrete problem arises: how does the surgeon know exactly where to operate? Without localisation, the surgeon would be operating blind — with a significant risk of missing the target or removing an excessive volume of healthy tissue. Pre-operative localisation is the technical solution to this problem: it consists in placing, within the breast, a physical marker that the surgeon can identify in theatre to guide the procedure.
Key point: pre-operative localisation turns an invisible and impalpable lesion into a tangible target for the surgeon. It is essential for any surgery of a non-palpable lesion, whatever its nature — cancer, at-risk lesion (ADH, LCIS, radial scar), papilloma, or a simple benign nodule to be removed.
Localisation is indicated as soon as a breast lesion to be operated on is not clinically accessible — i.e. cannot be found under the surgeon's fingers in theatre. In practice, this concerns: small breast cancers detected at screening, atypical ductal hyperplasia (ADH) and other B3 lesions, papillomas, suspicious foci of microcalcifications (BI-RADS 4 or 5), small ultrasound nodules that are deep or poorly defined, and certain lesions detected only on MRI with no ultrasound correlate — which then require MRI-guided localisation, a rarer and more complex procedure.
Source: SENORIF 2025-2026 · SFSPM
Before any surgery, there has almost always been a biopsy. During this biopsy — ultrasound-guided core biopsy for a nodule, stereotactic vacuum-assisted excision for microcalcifications, MRI-guided biopsy for an MRI-only lesion — the radiologist samples one or several fragments of breast tissue. At the end of the procedure, a small metal clip of a few millimetres, usually titanium, is systematically deposited at the exact site of sampling.
The most widely used clips are Twirl, Tumark, and UltraClip. They are biologically inert, painless, and fully compatible with mammography, ultrasound and breast MRI. They can remain in place indefinitely without any drawback.
After a biopsy — especially for microcalcifications or a small lesion — it is very common for the target to have entirely disappeared from imaging: the biopsy itself removed it all. If no clip had been placed, it would then be impossible to find precisely where the sampling had been done. The clip therefore acts as a lasting anatomical reference point. It serves two purposes:
If no surgery is decided (benign result, surveillance), the clip allows accurate radiological follow-up. At each control mammogram, the radiologist can review the exact biopsied zone and confirm its stability.
If surgery is decided, the clip serves as the target for pre-operative localisation. The localisation marker (hookwire or magnetic seed) is placed at the metal clip — pointing to it. By removing the marker and the clip, the surgeon mechanically removes the area of interest.
In short: a metal clip is always placed during a biopsy of a non-palpable lesion — it is good practice that protects the patient by keeping a physical trace of the biopsied zone, whatever the histological result and whatever the subsequent decision.
Source: SENORIF 2025-2026 · HAS
Two main pre-operative localisation techniques are currently available. Both are validated and effective; they differ mainly in logistics and patient comfort. The choice depends on availability at the radiology centre, lesion topography, care pathway organisation and patient preference.
A thin metal wire with one end anchored in the breast at the biopsy clip and the other end exiting the skin. Placed the evening before or the morning of surgery, under ultrasound or stereotactic guidance.
A few hours (same day) to 24 h maximum
A small magnetic marker of about 5 mm (Magseed, Localizer, Sirius, Savi Scout) placed at the metal clip. Detected intra-operatively by a dedicated magnetic probe.
Several days to several weeks (even months)
The goal is strictly the same in both cases: enable the surgeon to precisely locate the lesion in theatre. The oncological outcome is equivalent — it is not a question of surgical quality, but of organisation. The question is therefore not "which technique is best?" but "which is most suited to this patient, at this centre, for this lesion?".
Source: SFSPM · SENORIF 2025-2026
The hookwire, also called wire localisation or guidewire, is the historical technique for pre-operative breast localisation. In use since the 1970s, it remains today the most widely available method — available at every breast radiology centre, reliable, well-established, inexpensive.
A very thin metal wire (not unlike a fishing line in appearance) is introduced into the breast through a carrier needle, under ultrasound or mammographic guidance. The inner end of the wire carries a small hook which anchors in breast tissue at the biopsy clip. The needle is then withdrawn and the wire stays in place, with its outer end exiting the skin — covered by a sterile dressing.
The patient arrives at the radiology practice. If localisation is done the day before, no fasting required. If done the same morning, she arrives fasting, typically between 7:30 and 9:00 am. The specialist breast radiologist reviews the images, discusses the procedure and prepares the patient.
Antiseptic cleansing, local anaesthesia in the skin and breast tissue, placement of the hookwire under ultrasound or stereotactic guidance. Duration: 15 to 20 minutes.
X-ray check, dressing, and direct transfer to theatre with the images. The patient remains fasting and does not remove the dressing before surgery.
Universal availability: all breast radiology practices offer this technique.
Proven reliability: 50 years of experience, very high success rate.
Cost: inexpensive, well reimbursed by French national health insurance. Note: in the private sector, additional fees (dépassements d'honoraires) may apply depending on the radiology practice.
Constraining logistics: if localisation is done on the same morning, the patient must arrive fasting at the radiologist, then at theatre, with tight timing. If done the day before, no fasting required for placement — but the patient must attend twice (radiologist the day before, theatre the next day).
Wire exiting the skin: uncomfortable, anxiety-inducing for some patients, theoretical risk of displacement.
Time dependency: surgery must follow quickly. If surgery is postponed, the hookwire must be removed and replaced later.
Source: SFSPM · HAS
Developed in the 2010s, magnetic seeds represent a significant evolution in pre-operative localisation. Marketed under various names — Magseed (Endomag), Localizer (Hologic), Sirius, Savi Scout (Cianna Medical) — they share a common principle: a small magnetic metal capsule detected intra-operatively by a dedicated probe. These devices are being progressively deployed, with variable availability across radiology centres.
The magnetic seed is a metal capsule of about 5 mm in length, made of medical-grade stainless steel. It is introduced into the breast through a carrier needle, under ultrasound or mammographic guidance, and deposited immediately at the biopsy metal clip. The needle is then withdrawn — unlike the hookwire, nothing exits the skin. The seed rests silently in place until surgery.
In theatre, the surgeon uses a magnetic detection probe (e.g. Sentimag for Magseed) that emits an audible signal proportional in intensity to proximity to the seed. The closer the probe, the stronger the signal — the surgeon follows the signal to locate the target precisely, then removes the tissue surrounding the magnetic seed and the biopsy metal clip.
Standard appointment at the radiology practice, no fasting, at a convenient time for the patient. Placement of the magnetic seed under local anaesthesia, with ultrasound or mammographic guidance.
The patient resumes normal activities immediately after placement. The seed is entirely painless, invisible, and does not interfere with movement, sleep, sport or daily life.
Direct arrival at theatre, fasting, with no intermediate step at the radiologist. The surgeon uses the magnetic probe to locate the seed during the operation.
Decoupled logistics: placement several weeks before surgery, appointment independent of theatre.
Patient comfort: no wire exiting the skin, no anxiety on surgery day linked to localisation, no prolonged fasting.
Flexibility: surgery can be postponed without removing the seed, which remains active for several weeks.
Surgical precision: the probe allows fine guidance of the surgical gesture, often judged more comfortable by experienced operators.
Diagnostic safety: placement several weeks before surgery allows time for a full radiological review and, if needed, for additional biopsies in the same or the contralateral breast before the definitive surgical procedure.
Limited availability: not all radiology centres are equipped — deployment ongoing.
Cost: today fully reimbursed by French national health insurance and well covered. Note: in the private sector, additional fees (dépassements d'honoraires) may apply depending on the radiology practice.
MRI artefact: the seed generates a localised artefact on follow-up MRI (blur zone around the seed) — usually not a problem in practice.
Source: Endomag (Magseed), Hologic (Localizer), clinical studies 2018-2024
Here is the full step-by-step journey, from the biopsy to the histopathological analysis of the specimen. This is the sequence familiar to every patient managed for a non-palpable breast lesion.
Core biopsy or vacuum-assisted excision at the radiology practice. Placement of the metal clip (Twirl, Tumark, UltraClip) at the exact sampling site.
Biopsy results, consultation with the surgeon, discussion at the MDT when appropriate, decision to proceed with surgical excision, scheduling.
Placement of the hookwire on the day of surgery, or the magnetic seed several weeks before. At the biopsy metal clip, under local anaesthesia.
En-bloc removal of the localisation marker, the metal clip and the surrounding lesion. Specimen radiograph for verification. Sent to pathology.
Option A — day before surgery: hookwire placed at radiology during the day, no fasting required. Return home or hotel with the dressing. Next morning, arrival at theatre, fasting.
Option B — morning of surgery (D0): arrival at the radiology practice early in the morning, fasting; hookwire placed; direct transfer to theatre in the following hours.
Evening of D0 or D+1: discharge home.
D-30 to D-7: magnetic seed placed at radiology, no fasting, during the day.
In between: normal life, no restrictions.
D0: direct arrival at theatre, fasting. Surgery.
Evening of D0 or D+1: discharge home.
Source: SENORIF 2025-2026
A step often unknown to patients, but systematic in any localisation-guided surgery: the specimen radiograph. It is an essential verification step, performed on the spot, before skin closure.
Once the surgeon has removed the fragment of breast tissue theoretically containing the lesion, the localisation marker and the metal clip, the specimen is sent to the radiology room adjacent to theatre (or X-rayed directly in theatre, depending on the centre), before being transmitted to the pathology laboratory. A simple mammogram of the fragment is performed. This specimen radiograph provides several decisive pieces of information within minutes.
The biopsy metal clip is visible on the specimen X-ray. If so, the target has been reached: the surgeon has removed the area of interest.
The hookwire or magnetic seed must also be present in the specimen — additional confirmation that the targeted zone has been retrieved.
When the initial target was a focus of microcalcifications, their presence on the specimen X-ray confirms that the entire focus has been removed.
The position of the clip and microcalcifications relative to the margins of the specimen gives a first appreciation of margin status — completed by the histopathological analysis.
This is a rare but anticipated situation. If the specimen X-ray shows neither the clip nor the target microcalcifications, the target has not been reached — the surgeon has not removed the correct zone. In this case, a further resection is performed during the same operative time: the surgeon re-aims with the localisation marker, removes more tissue, and an X-ray of the new specimen is repeated until verification. This control step is an integral part of procedural safety — it prevents late discovery that the target has not been reached.
In practice: the specimen radiograph is systematic after any localisation-guided excision. It guarantees to the patient and the team that the target has indeed been reached — it is a quality standard in modern breast surgery.
Source: SFSPM · SENORIF 2025-2026
Paris 8th practice · Clinique Hartmann Neuilly · French sector 2 (non-OPTAM)
The answers below are drawn from daily clinical practice and current guidelines.
No, or very little. Localisation is performed under local anaesthesia by the specialist breast radiologist. A small injection is given into the skin and breast tissue before placement of the hookwire or magnetic seed. The procedure takes 10 to 20 minutes depending on technique and location. You may feel pressure or a slight pulling sensation with the hookwire, but pain is very limited. A mild haematoma is possible, resolving spontaneously in a few days.
Neither is superior to the other in terms of oncological outcome. Both techniques allow the surgeon to locate the lesion precisely — which is exactly the goal. The difference lies in logistics and comfort: the magnetic seed significantly simplifies the pathway by allowing placement several weeks before surgery, with no wire exiting the skin. The hookwire remains very reliable and universally available. The final choice depends on availability at the radiology centre, lesion topography, and your preferences.
Depending on the device, from several days to several months. Available devices (Magseed, Localizer, Sirius, Savi Scout) allow placement sufficiently far in advance of surgery to fully decouple localisation logistics from theatre. This flexibility is one of the major strengths of the magnetic seed: it allows surgery scheduling without any localisation-related constraint, and also permits a full radiological review or additional biopsies in the same or the other breast before the definitive surgical procedure.
No. The magnetic seed is very small (about 5 mm) and its magnetic signature is too weak to trigger airport gates, shop anti-theft devices or everyday detectors. You can travel and pass security checks without any particular constraint.
Both techniques adapt to all breast morphologies and lesion depths, with a few nuances. The hookwire can be trickier to position in a very dense breast or for a very deep lesion — but the specialist breast radiologist adapts the technique case by case. The magnetic seed is more versatile in this context. When difficulty is anticipated, discussion between surgeon and radiologist before localisation allows the best strategy to be planned.
The theoretical risk exists — that is why the hookwire is placed shortly before surgery (a few hours to 24 hours maximum). In practice, the modern hookwire has an anchoring hook that holds it firmly in place. It is protected by a thick dressing, and it is recommended to limit sudden movements and avoid carrying heavy loads between placement and surgery. Significant displacement is rare; if the position seems uncertain, a new X-ray is taken before the procedure.
Yes. When several non-palpable lesions must be removed during the same procedure, multiple localisations can be placed — one per lesion. Hookwires can be multiple, as can magnetic seeds, although some probes have resolution limits between two very close seeds. The radiologist and surgeon discuss the strategy in advance to optimise positions.
Yes, both techniques are reimbursed by French national health insurance. The hookwire is well reimbursed — a historical and inexpensive technique. The magnetic seed (Magseed, Localizer, Sirius) is today fully reimbursed by French national health insurance and well covered. Note however: in the private sector, additional fees (dépassements d'honoraires) may apply — whether for hookwire or magnetic seed — depending on the radiology practice and its convention with national health insurance. Always ask the practice for a prior quote stating the tariff and any out-of-pocket cost.
It is removed with the surgical specimen. This is in fact one of the explicit goals of surgery: to remove en-bloc the localisation marker (hookwire or magnetic seed), the biopsy metal clip and the surrounding lesional tissue. The specimen radiograph confirms its presence in the resected fragment. After surgery, there is therefore no clip left in the breast.
Yes, if the delay exceeds a few hours. The hookwire is designed to stay in place for a very short time. If for any reason surgery is cancelled or postponed beyond 24-48 hours, the hookwire must be removed by the radiologist, then repositioned before the new surgical date. That is one of the reasons why, when possible, the magnetic seed offers more flexibility: it can stay in place for several weeks without drawback, even if surgery is postponed.
Pre-operative localisation is a technical step that occurs in the pathway of many breast conditions. Here are the pages that go deeper into the clinical situations in which it is indicated.
The highest-risk B3 lesion, diagnosed on stereotactic vacuum-assisted excision and almost systematically operated with pre-operative localisation.
At-risk lesion often non-palpable, diagnosed on core biopsy. Surgical excision, when decided, is guided by pre-operative localisation.
All benign and at-risk breast lesions: classification, management, follow-up. The parent page that places each situation in context.
This page draws on French and international breast oncology guidelines, the recommendations of learned societies, and the medical literature indexed on PubMed.
Last revision of this page: 22 April 2026 · Next update planned: October 2026.
Paris 8th practice or Clinique Hartmann Neuilly. Second opinion on file.