Histologic comparison of the area of tumor bed after vacuum-assisted biopsy (VAB) or standard breast surgery in patients with early breast cancer after neoadjuvant systemic therapy (NST).

e12573 Background: The main goal of surgical intervention after achieving complete clinical response is to confirm it pathmorphologically. VAB of the tumor bed in the breast has demonstrated encouraging results as a minimally invasive method to determine pCR. It is not yet known whether the tumor bed can be accurately measured in the fragmented VAB material and therefore RCB index cannot be determined. From the point of view of pathologic examination, it is crucial to confirm that specimen volume after VAB is sufficient for precise assessment of the tumor bed. Methods: A single-center retrospective study included 36 patients with unifocal breast cancer (cT1-2N0-1M0). First group of patients underwent VAB instead of standard surgery as part of clinical trial NCT04293796. Second group includes patients after standard breast-conserving surgery (BCS) or mastectomy. All patients included in the analysis achieved pCR after NST. All microscope slides after preliminary cleaning were digitized using 3DHistech PANNORAMIC 1000 DX scanner. Tumor bed measurements were performed manually by experienced pathologist using the 3DHistech SlideViewer 2.8.0 software. Tumor bed area (mm 2 ) was selected as main tumor bed characteristic. Results: 36 patients were included in the analysis (20 women after VAB and 16 women after standard surgery). Mean tumor bed area in specimens obtained by VAB was 266.67 mm 2 (30.50–740.08), after BCS and mastectomy - 199.88 mm 2 . (48.67–740.6). There was no statistically significant difference in tumor bed area depending on type of intervention performed (U-test=126.0, p=0.286). No differences were observed between groups after standardization of tumor bed area measurements in each group (U-test after MinMax standardization: 117.5, p=0.181; U-test after Robust standardization: 166.0, p=0.861). Correlation analysis using Spearman’s method was performed to assess correlation between tumor bed area and quantitative clinical variables: maximum tumor size before NST (r=0.143, p=0.418), maximum tumor area before NST (r=0.113, p=0.523), maximum tumor size after NST (r=-0.161, p=0.360) and maximum tumor area after NST (r=-0.114, p=0.520). There was a significant correlation between tumor bed area and total area of VAB specimen (r=0.605, p=0.0047). Associations with categorical variables were analyzed using Kruskal-Wallis test: cT stage (0.516, p=0.473), cN stage (0.660, p=0.417), clinical stage (1.473, p=0.479). Conclusions: There is no statistically significant difference in tumor bed area measurements depending on type of surgery performed. Volume of specimen after VAB is enough for tumor bed assessment as in the specimens after standard surgery.