Real-time intraoperative detection of breast cancer using near-infrared fluorescence imaging and Methylene Blue

Abstract

Background

Despite recent developments in preoperative breast cancer imaging, intraoperative localization of tumor tissue can be challenging, resulting in tumor-positive resection margins during breast conserving surgery. Based on certain physicochemical similarities between Technetium(^99mTc)-sestamibi (MIBI), an SPECT radiodiagnostic with a sensitivity of 83–90% to detect breast cancer preoperatively, and the near-infrared (NIR) fluorophore Methylene Blue (MB), we hypothesized that MB might detect breast cancer intraoperatively using NIR fluorescence imaging.

Methods

Twenty-four patients with breast cancer, planned for surgical resection, were included. Patients were divided in 2 administration groups, which differed with respect to the timing of MB administration. N = 12 patients per group were administered 1.0 mg/kg MB intravenously either immediately or 3 h before surgery. The mini-FLARE imaging system was used to identify the NIR fluorescent signal during surgery and on post-resected specimens transferred to the pathology department. Results were confirmed by NIR fluorescence microscopy.

Results

20/24 (83%) of breast tumors (carcinoma in N = 21 and ductal carcinoma in situ in N = 3) were identified in the resected specimen using NIR fluorescence imaging. Patients with non-detectable tumors were significantly older. No significant relation to receptor status or tumor grade was seen. Overall tumor-to-background ratio (TBR) was 2.4 ± 0.8. There was no significant difference between TBR and background signal between administration groups. In 2/4 patients with positive resection margins, breast cancer tissue identified in the wound bed during surgery would have changed surgical management. Histology confirmed the concordance of fluorescence signal and tumor tissue.

Conclusions

This feasibility study demonstrated an overall breast cancer identification rate using MB of 83%, with real-time intraoperative guidance having the potential to alter patient management.

Introduction

Breast cancer is the most common malignancy in women worldwide and is a leading cause of cancer-related mortality.¹ More than 1.2 million cases are diagnosed every year, affecting 10–12% of the female population and accounting for 500,000 deaths per year worldwide.

In early breast cancer, breast conserving surgery (BCS) is the preferred standard of care. Despite preoperative imaging modalities such as CT and MRI, intraoperative identification of breast cancer tissue can be challenging. Previous studies reported that the incidence of tumor cells at or near the cut edge of the surgical specimen ranged from 5% to 82%, with the majority of studies indicating positive resection margins in 20%–40% of patients after resection of the primary tumor.² Positive margins may lead to additional surgical procedures, delays in adjuvant treatment, increased morbidity, poor aesthetic results, and increased healthcare costs. Therefore, there is an urgent need for new technology to identify breast cancer tissue intraoperatively.

Technetium(^99mTc)-sestamibi (MIBI) is a lipophilic cation used for preoperative, non-invasive identification of malignant tissue via SPECT imaging.³ Using ^99mTc-MIBI, preoperative identification of breast cancer is possible in approximately 83–90% of patients.3, 4, 5 Based on the lipophilic, cationic structure of Methylene Blue (MB), and the fact that like ^99mTc-MIBI, MB can function as a perfusion tracer in vivo,6, 7 we hypothesized that it too might be able to detect breast tumors. Importantly, MB is a clinically available tracer that can be used at relatively low dose (0.5–1 mg/kg) as a fluorescent tracer during NIR fluorescence imaging. NIR fluorescence imaging is a promising technique to assist in the intraoperative identification of sentinel lymph nodes, tumors, and vital structures.⁸

During ^99mTc-MIBI SPECT imaging, early (within 30 min after tracer administration) and delayed (3 h post tracer administration) imaging is performed in succession.5, 9 The reason for this is to differentiate more accurately between malignant and benign lesions because it is presumed that tracer uptake in malignant lesions might persist, whereas clearance from benign lesions would be more rapid. Delayed imaging could thereby result in higher tumor-to-background ratios (TBRs) from lower background signal.

The aim of this study was to determine the feasibility of using MB as an NIR fluorescent tracer for the identification of breast tumor intraoperatively, and to compare early and delayed imaging protocols.