ICG fluorescence imaging as a new tool for optimization of pathological evaluation in breast cancer tumors after neoadjuvant chemotherapy

Response to neoadjuvant chemotherapy (NACT), particularly pathologic complete response (pCR), is an independent predictor of favorable clinical outcome in breast cancer (BC). The accuracy of residual disease measurement and reporting is of critical importance in treatment planning and prognosis for these patients. Currently, gross pathological evaluation of the residual tumor bed is the greatest determinant for accurate reporting of NACT response. Fluorescence imaging (FI) is a new technology that is being evaluated for use in the detection of tumors in different oncological conditions. The aim of this study was to evaluate whether indocyanine green fluorescence imaging (ICG-FI) is able to detect residual breast tumor tissue after NACT in breast surgical operative specimens. Patients who underwent NACT for BC and were admitted for breast surgery were selected for participation in this study. Free ICG (0.25 mg/kg) was injected intraoperatively. Tumor-to-background fluorescence ratio (TBFR) was calculated on ex vivo samples from the surgical specimen. One hundred and seventy-two samples from nine breast surgical specimens were evaluated for their fluorescence intensity. Among them, 52 were malignant (30.2%) and 120 were benign (69.8%). The mean TBFR was 3.3 (SD 1.68) in malignant samples and 1.9 (SD 0.97) in benign samples (p = 0.0002). With a TBFR cut-off value of 1.3, the sensitivity, specificity, negative predictive value, false negative rate, and false positive rate of ICG-FI to predict residual tumoral disease in breast surgical samples post-NACT were 94.2%, 31.7%, 92.7%, 5.8%, and 68.3%, respectively. If we restricted our analysis to only patients who achieved pCR, the negative predictive value for ICG-FI was 100%. These first observations indicate that ex vivo ICG-FI is sensitive but not sufficiently specific to discriminate between benign breast tissue and malignant residual tissue. Nevertheless, its negative predictive value seems sufficiently accurate to exclude the presence of residual breast tumor tissue on the operative specimen of patients treated by NACT, representing a potential tool to assist pathologists in the assessment of breast surgical specimens.