Utility of photoacoustic patterns in intra-operative margin assessment of breast cancer post neoadjuvant chemotherapy.

Purpose: To evaluate the feasibility and accuracy of ultrasound-guided photoacoustic tomography (US-PA) for intraoperative margin assessment in breast-conserving surgery (BCS) following neoadjuvant chemotherapy (NACT). Methods: This study, approved by the local Institutional Review Board, included 21 women with histologically confirmed breast cancer referred for BCS post-NACT. Data from 4 participants were used for training while 17 participants were analyzed. US-PA imaging was performed using the MSOT inVision 512-ECHO system, capturing chromophores like lipids, collagen, and hemoglobin up to a 5 mm depth. Imaging results were compared to histopathological findings, and diagnostic accuracy was calculated. Results: US-PA imaging demonstrated a high diagnostic accuracy of 89.0 %, with a sensitivity and negative predictive value (NPV) of 100 %, specificity of 86.9 %, and positive predictive value (PPV) of 59.4 %. Excellent inter-observer agreement (kappa = 1) was observed. No laser-induced tissue damage was noted. The average scan time per specimen was approximately 20 minutes. False positives (n = 11) were primarily due to post-therapy fibrotic changes and extremely close tumor extensions (<2 mm). Conclusion: US-PA provided clear visualization of tissue components, accurately correlating with histopathology. The method's high NPV minimizes the risk of re-operations and locoregional recurrence. Although the PPV was lower, it did not impact clinical management as surgeons typically excise wider margins in such cases. The study highlighted US-PA's potential as a promising tool for intraoperative margin assessment in BCS post-NACT, offering a rapid, accurate, and safe method. Further studies with larger sample sizes are needed to confirm these findings and enhance quantitative assessment methods.