Background: Superparamagnetic iron oxide (SPIO) nanoparticles is a magnetic sentinel lymph node (SN) tracer. Since no radioisotope (technetium, Tc99) is used, there is no need for a nuclear medicine department. Compared to the use of Patent Blue V® (PB), no allergic reactions have been reported so far. However, a long lasting skin staining has been observed. We compared skin staining in women who were injected with both SPIO (MagTrace®) and PB. Methods: SPIO, Tc99 and PB were injected in all women in the SentiDose study (2017-2019), a SPIO dose optimizing trial, including six Swedish hospitals. For PB, a 1.0ml sub/intradermal, peri-areolar injection was administred. For SPIO either a 1.5ml retro-areolar (Cohort 1.5, n=163) or a 1.0ml peri-tumoral (Cohort 1.0, n=164) interstitial injection was administred. Staining was assessed by telephone interviews at 6, 12 and 24 months post surgery, and mean size calculations only included women with a stain. Mastectomy cases (n=63) were excluded from the analysis. SN detection rates will be reported elsewhere. Results: In Cohort 1.5, 27.7% (33/119) of the women had a SPIO stain and 25.2% (30/119) a PB stain at 6 months (p=0.66). The mean stain sizes were 13.4 and 9.1cm2 (p=0.16), respectively. At 12 months, 20.8% still had a SPIO stain and 17.6% a PB stain (p=0.91), with mean sizes of 4.1 and 3.7 cm2 (p=0.73), respectively. At 24 months, from the 11 women followed so far, all 3 with an earlier SPIO stain and 7 of 8 with an earlier PB stain are now stain free. In Cohort 1.0, 16.5% (25/145) had a SPIO stain and 16.9% (24/139) had a PB stain at 6 months (p=0.94). The mean stain sizes were 11.8 and 8.4 cm2 (p=0.42), respectively. Nine women were not injected with PB. After 12 months, 15.9% still had a SPIO stain and 12.4% a PB stain (p=0.42). The mean sizes were 5.1 and 2.6 cm2 (p=0.99), respectively. Comparing all women at 6 months, 22.0% had a SPIO stain and 20.5% a PB stain (p=0.12) with mean sizes 12.5 and 8.6 cm2 (p=0.83), respectively. At 12 months, 17.8% had a residual SPIO stain and 14.9% a PB stain (p=0.37) with mean sizes 4.6 and 3.3 cm2 (p=0.16), respectively. The difference in incidence of SPIO staining between Cohort 1.5 and Cohort 1.0 was statistically significant at 6 months, but not at 12 months, 27.7% vs. 16.5%, (p=0.04) and 20.8% vs 15.9% (p=0.28), respectively. The difference in SPIO stain sizes between the cohorts was neither significant at 6 months, 13.4 vs 11.8 cm2(p=0.61) nor at 12 months, 4.1 vs 5.1 cm2 (p=0.30). Conclusion: No statistically significant differences in incidence or stain size were observed between SPIO and PB. The 2-year follow up will be completed during 2021. The 1.0ml compared to 1.5ml SPIO dose, resulted in fewer but equally large stains at 6 months, but there was no difference at 1 year.

Table 1. Skin staining after SPIO and Patent Blue (PB) for sentinel lymph node detection

TracerStaining/SizeStaining/Size
 6 months 12 months 
SPIO 1.5ml, n=119 27.7%/13.4cm2 20.8%/4.1cm2 
SPIO 1.0ml, n=145 16.5%/11.8 cm2 15.9%/5.1 cm2 
PB, n=258 20.5%/8.6 cm2 14.9%/3.3 cm2 
TracerStaining/SizeStaining/Size
 6 months 12 months 
SPIO 1.5ml, n=119 27.7%/13.4cm2 20.8%/4.1cm2 
SPIO 1.0ml, n=145 16.5%/11.8 cm2 15.9%/5.1 cm2 
PB, n=258 20.5%/8.6 cm2 14.9%/3.3 cm2 

Citation Format: Madeleine Warnberg, Andreas Karakatsanis, Fredrik Nilsson, Christine Obondo, Lida Pistiolis, Imad Mohammad, Carlos Dussan Luberth, Staffan Eriksson, Abdi-Fatah Hersi, Fredrik Wärnberg. A prospective comparison of skin staining after sentinel lymph node biopsy, using blue ink (PB) and superparamagnetic iron oxide nanoparticles (SPIO) tracers [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PS1-52.