Magnetic Lymphatic Tracing for Omission of Sentinel Lymph Node Biopsies in Mastectomy Patients: A Community Cancer Center Experience

BACKGROUND Patients with ductal carcinoma in situ (DCIS) and patients undergoing risk reduction mastectomy may undergo sentinel lymph node biopsy (SLNB) at the time of mastectomy to complete axillary staging were an underlying invasive malignancy to be found on final pathology. Amongst patients with DCIS undergoing mastectomy, 15-29% of patients will have invasive disease on final pathology; therefore, approximately 70-85% of patients may benefit from avoiding SLNB. Superparamagnetic tracers (SPMT) have been proven to be non-inferior to the standard radioisotope and blue dye combination. SPMT remains active for several weeks, allowing a large proportion of DCIS and genetic carrier patients to potentially avoid SLNB in the setting of mastectomy. We hypothesize the use of SPMT will reduce the number of SLNB performed in patients undergoing mastectomy for DCIS and risk reduction, ultimately reducing the number of complications associated with axillary surgery. We seek to report our community cancer center’s experience with SPMT and omission of SLNB in the DCIS and prophylactic mastectomy patient population. METHODS We performed a retrospective review of 52 female patients with DCIS or known genetic predisposition undergoing mastectomy. SPMT (Magtrace®) was injected ipsilateral to DCIS and bilaterally for prophylactic mastectomy patients. Our primary outcome was rate return to the operating room (OR) for delayed SLNB. Secondary outcomes included post operative complications within 30 days of surgery and OR times. We compared outcomes to a control group of 28 women undergoing mastectomy for DCIS or risk reduction who underwent SLNB at their index operation in traditional fashion. Continuous variables were reported using median and interquartile ranges (IQR) and were compared using the Mann-Whitney U-test. Categorical data were reported using frequency and percent and were compared using Pearson’s Chi-Square or Fisher’s Exact test, as appropriate. Alpha was set to 0.05 to determine statistical significance. RESULTS There were a total of 80 patients (52 SPMT, 28 control). Median age of SPMT patients was 49.5 years (IQR 40-60.75) vs. 54.5 (IQR 48-65) years in the traditional tracer, control group. 57.7% of SPMT patients underwent mastectomy for DCIS vs. 89.3% in the control group. 8 SPMT patients (15.4%) had invasive ductal carcinoma (IDC) on final pathology and 7 of those patients underwent delayed SLNB. None of the delayed SLNB were positive for metastatic disease. Rates of post operative complications were similar between the groups, including hematoma, seroma, and surgical site infection. OR times were also similar with median OR time 202 minutes (min) for the SPMT group vs. 195 min for the control group. CONCLUSION Use of SPMT avoided SLNB in 84.6% of our patients. We found no difference in rates of postoperative complications or operative times in patients using SPMT for omission of SLNB at time of mastectomy compared to the control group. Our findings suggest SLNB can be avoided in a majority of patients undergoing mastectomy for DCIS or risk reduction in the setting of genetic predisposition.