Methylene blue sentinel lymph node biopsy for breast cancer learning curve in the COVID-19 era: How many cases are enough? [version 1; peer review: 2 approved with reservations]

Background: Sentinel lymph node biopsy (SLNB) is now the gold standard procedure for early breast cancer with clinically negative lymph nodes (N0). According to the Indonesian Board-Certified oncologist surgeon, the learning curve for evaluating fellow breast surgeons to achieve this competency could have been shorter due to the COVID-19 pandemic. This study aims to see if the learning curve for sentinel lymph node (SLN) identification can be shortened and if imprint cytology (IC) can replace frozen sections (FS) for intraoperative analysis. Methods: Fellow breast surgeons were taught to perform SLNB on breast cancer patients. Intraoperative assessment and completion of axillary lymph node dissection (ALND) were performed in the first setting for standardization with the attending surgeon. Sentinel lymph node (SLN) identification was plotted on cumulative sum chart (CUSUM) limitations for evaluating the variability competency between attending surgeon and fellow surgeon based on a target identification rate of 85%. In addition, the accuracy of imprint cytology versus frozen section for identifying lymph node metastases was compared. Results: Consecutive 50 SLNBs were conducted during this period with attending and trainees split into two groups. After 13 consecutive tests, the CUSUM plot positively identified SLN as a significant achievement level of competency. Imprint cytology was shown to be inferior to frozen section cytology. The accuracy of imprint cytology is 91.8%, while the accuracy of frozen sections is 95.9%. Conclusion: According to a CUSUM chart based on a reasonable set of parameters, the learning curve for SLNB using methylene blue dye is reached after 13 consecutive positively detected SLN. Meanwhile, the frozen section is still the gold standard for determining the disorder of axillary lymph nodes, but the accuracy between the two methods can be comparable.