The Number of Sentinel Lymph Nodes Could be Optimized by Adjusting the Injection Dose

Background: The optimal number of sentinel lymph nodes (SLNs) to be removed is controversial based on the false negative rate and prognosis. We investigated factors related to the number of SLNs and the possibility of optimizing the number of SLNs. Methods: We retrospectively reviewed 167 cases in which 0.3 or 0.5 ml of ferucarbotran was sub-dermally injected without massage from July 2016 to November 2018. Sentinel lymph node biopsy (SNB) was conducted using both radioisotope (RI) and superparamagnetic iron oxide (SPIO). The removed nodes with a value of ≥0.5 μT on a magnetometer were considered to be SLNs (SPIO nodes). The total SPIO node count in each case was calculated. Results: There was a significant correlation between the number of SPIO nodes and total count of SPIO nodes (rs=0.821, p<0.0001). With RI and SPIO methods, the average number of removed nodes in the age≥75 years and BMI≥25 subgroups was significantly lower than that in the age<75 years and BMI<25 subgroups. The number of SPIO nodes was significantly influenced by the injected dose. The average number of SPIO nodes in the age ≥75 years and BMI≥25 subgroups after injection of 0.5 ml was almost the same as that of the age <75 years and BMI<25 subgroups after injection of 0.3 ml. Conclusion: Obesity and old age seemed to be associated with slow lymphatic flow; however, increasing the dose increased the number of SPIO nodes. Thus, optimization of the number of SLNs seems possible.