Purpose: Sentinel Lymph Node Biopsy (SLNB) is currently the standard of care in clinical node negative (cN0) early breast cancer. The aim of this study is to evaluate the negative predictive value of 18F-FDG dedicated axillary PET (DA-PET) and to verify whether SLNB can be omitted in patients with negative preoperative axillary assessment.

Patients and Methods: SOAPET is a prospective phase II trial consisted of 2 stages (NCT04072653). In the first stage, cN0 patients detected by clinical examination, received routinely axillary imaging evaluation (ultrasound and CT etc) and DA-PET, then received SLNB. In the second stage, SLNB will be omitted in the patients with negative preoperative axillary assessment after integrate DA-PET. Now we report the results of the first stage, the primary outcome is negative predictive value (NPV) of DA-PET to detect non-macrometastases of lymph nodes.

Results: From Sep 9, 2019 to May 30, 2020, 224 patients were screened, and 189 patients with invasive breast cancer (180 invasive ductal carcinoma, 9 invasive lobular carcinoma) received DA-PET followed by surgical operations with definitive pathological reports. Media tumour size was 2.2cm, 120 HR+HER2-, 23 HR+HER2+, 27 HR-HER2+, 19 HR-HER2-. 40 patients had at least 1 macrometastases lymph nodes (8 patients had over 3 nodes involved), and 16 patients had only micrometastasis nodes. Among 131 patients with DA-PET negative (maxSUV<0.27), 16 patients had macrometastases lymph nodes and 11 patients had micrometastasis diseases. For 58 patients with DA-PET positive (maxSUV>=0.27), 24 patients had macrometastases and 5 patients had micrometastasis nodes. The NPV of DA-PET was 87.8%. The NPV of ultrasound was 86.3%. When combine axillary imaging evaluation with ultrasound and DA-PET, 100 patients were screened out with both DA-PET and ultrasound negative, among which 9 patients had macrometastases and 9 patients had micrometastasis nodes, the NPV was 91%. Conclusions: DA-PET can be used to identify cN0 patients, reducing the false negative rate < 10%. The second stage of SOAPET trial is ongoing to validate the safety of omitting SLNB according to preoperational axillary evaluation when integrating DA-PET. Key words: Breast cancer, Sentinel lymph node biopsy; Dedicated PET;18F-FDG;

Table 1: Axillary lymph node detection efficiency of ultrasound and DA-PET

Axillary imaging assessmentPatients nmacrometastasesmicrometastasis only
ultrasound*  40 16 
US-neg 124 17 12 
US-det 46 14 
US-met 19 
DA-PET**    
negative 131 16 11 
positive 58 24 
Axillary imaging assessmentPatients nmacrometastasesmicrometastasis only
ultrasound*  40 16 
US-neg 124 17 12 
US-det 46 14 
US-met 19 
DA-PET**    
negative 131 16 11 
positive 58 24 

*:US-neg: no lymph nodes detected by ultrasound;US-det: lymph nodes detected by ultrasound;US-met: suspected metastatic lymph nodes detected by ultrasound**:Maximum single-voxel Standard Uptake Value (maxSUV) cutoff value of DA-PET was set at 0.27 (<0.27 is negative)

Table 2: Intergrate axillary imaging assessment with ultrasound and DA-PET

  macrometastases  
   
axillary imaging assessment 31 58 89 
 -* 91 100 
  40 149 189 
  macrometastases  
   
axillary imaging assessment 31 58 89 
 -* 91 100 
  40 149 189 

*:no lymph nodes detected by ultrasound and maxSUV in DA-PET < 0.27

Citation Format: Junjie Li, Jingyi Cheng, Guangyu Liu, Yifeng Hou, Genghong Di, Benlong Yang, Yizhou Jiang, Liang Huang, Sheng Chen, Yan Wang, Keda Yu, Zhimin Shao. A prospective phase II trial to evaluate the feasibility of omit sentinel lymph node biopsy after integrate18F-FDG dedicated axillary PET in early breast cancer: SOAPET trial [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 PS1-30.