Superparamagnetic iron oxide nanoparticles, a novel tracer in breast cancer surgery

The most common surgical choice of treatment in breast cancer is breast-conserving surgery (BCS) together with sentinel lymph node biopsy (SNB). Around 10% of breast cancer diagnosis are ductal carcinoma in situ (DCIS). Superparamagnetic iron oxide nanoparticles (SPIO) are a novel tracer for sentinel lymph node (SN) detection. The aim of this thesis was to investigate the unique applications and functionality of a magnetic approach in breast cancer surgery. Paper I was a two-centre pilot study of 32 patients with non-palpable breast cancer who were scheduled for BCS together with SNB. They received SPIO for SNB and a magnetic seed (Magseed®) for localization of the breast tumour. All 32 patients underwent microscopically radical resection and SNB was successfully performed in all included patients. Paper II was a multicentre prospective single-cohort study. It was a pre-planned interim analysis of 189 patients with “high-risk” DCIS who received SPIO at primary surgery but without performing SNB. If an invasive breast cancer was shown by the final histopathology report, the patient was scheduled for second surgery to undergo SNB. Because SPIO has a much longer half-life than the radioisotope, the magnetic signal at the second surgery was sufficient for detecting SNs; in fact, in patients with DCIS, it reduced from around 50% to 22%. Paper III was a multicentre prospective trial. Two consecutive cohorts of patients with breast cancer scheduled for SNB (n = 328) were included. Lower doses of a refined SPIO suspension were tested in different time frames and injection sites. Analyses were performed as a one-step individual patient-level meta-analysis using patient-level data from a similar previous cohort (n = 206) as a third reference group. In 534 patients, the SPIO SN detection rates were comparable (97.5% vs. 100% vs. 97.6%, p = 0.11) and were noninferior to the dual technique. Paper IV was a multicentre randomized pilot trial aimed to compare tumour localization in nonpalpable breast cancers using either Magseed® or guidewire in patients scheduled for BCS + SNB. All patients received SPIO for the SNB preoperatively. Patients who were randomized to the magnetic seed cohort received their Magseed® at the same time as the SPIO injection preoperatively while the guidewire placement was performed on the same day as surgery. In 207 patients, there were no significant differences in reoperation rate (3% in the magnetic seed cohort vs 7% in the guidewire cohort, p = 0.35).