Clinical Translation of Photoacoustic Tomography
The detection of regional lymph node metastases is important in cancer staging as it influences the prognosis of the patient and the strategy for treatment. Sentinel lymph node biopsy (SLNB) has emerged as the standard of care for axillary staging of clinically node-negative breast cancer.1,2 The SLN hypothesis states that the pathological status of the axilla can be accurately predicted by determining the status of the first (i.e., sentinel) lymph node(s) that drains from the primary tumor. Besides the presence of metastasis or micrometastasis detected in the SLN after excision and histological examination, the total number of involved regional lymph nodes is important in staging the disease, with the number predicting overall survival with an inverse relationship. Typically, the conventional SLNB procedure consists of injecting radioactive tracers and/or MB dye to mark the lymphatic system and guide the surgeon to the sentinel node. The radioactive tracer is injected a few hours prior to the surgery, while MB, which spreads relatively quickly through lymph vessels, is injected in the operating room. A few minutes following MB injection, a surgical incision is made in the area indicated by a handheld Geiger counter. The surgeon interrogates the axilla and identifies nodes that have been stained blue or nodes that are detected as radioactive with the Geiger counter. These nodes are then removed for histological examination to determine the presence of tumor metastases.