Safety and Feasibility Study of Magnetic Seed Markers to Localise Breast Cancers for Surgical Excision

Background and Rationale Breast Cancer Breast cancer is a heterogeneous disease, with great diversity in the site, size and progression of tumours. Some are palpable and discovered by the patient, though many are first detected during mammogram screening. For such cancers, localisation is necessary prior to surgery, to guide surgeons to the target excision site.

Wire Guided Localisation Traditionally, localisation involves radiographic-guided insertion of a wire into the breast, with positioning of the wire tip at the centre of the lesion. However, this procedure carries several logistical limitations , stemming from the fact that wire localisation must be performed on the day of surgery. This is to minimise risk of wire migration or dislodgement , a significant possibility due to the external section of wire left protruding from the breast. Same-day appointments demand excellent coordination between radiological departments and operating theatres to ensure that disruption to procedure scheduling is minimised. Delays may result from technically difficult procedures , leading to over-running radiology appointments that have a knock on effect on operating lists. Additionally, cancelled operations can result in preceding wire guidance procedures becoming unnecessary, resulting in wasted staff hours.

Another limitation of wire guidance occurs because the wire directs surgeons along a linear route. Lesions are found at a point along the wire, though it can be difficult to determine how far along they are found. For this reason, surgeons making initial incisions may be dictated by the visual trajectory of the wire, rather than the location of the lesion. This can lead to excessive dissection and sub optimal cosmetic results.

Radioactive Seed Localisation Radioactive seed localisation (RSL) is a localisation technique that is less commonly used in the United Kingdom (UK). A radioactive seed can be inserted up to 5 days before surgery, thus eliminating the requirement for radiology appointments on the same day as the patient's operation. The seed is detected in theatre using a handheld gamma probe. The gamma probe directs the surgeon to a single specific point via the shortest route, whereas, wires often transect the breast, meaning that surgeons commonly end up dissecting across normal tissue to locate the tip of the wire. In addition, with RSL, there is no distraction from external projections of wire, so the surgeon is guided purely by the audible response to the seed. It is hypothesised that the advantages of RSL will lead to improved surgical techniques and reduce pressures on theatre scheduling.

However, up to now, there is little evidence demonstrating clear superiority in surgical outcome of one localisation technique. Several studies have found lower positive margin rates in patients undergoing RSL versus wire guidance , , . This means that edges of excised tissues less commonly involves cancerous tissue, suggesting that RSL more accurately localises cancerous lesions. Conversely, many more studies, including one of the largest trials to date, conclude there is no variability in surgical outcome.