# Detection of Prostate Cancer Metastases During Pelvic Lymph Node Dissection with the PSMA-Targeted Fluorescent Agent OTL78: A Phase II Study

## TL;DR

This study tested a fluorescent tracer called OTL78 to detect prostate cancer metastases in lymph nodes during surgery, showing promising results in identifying cancerous nodes.

## Contribution

The study demonstrates the feasibility of using OTL78, a PSMA-targeted fluorescent agent, for intraoperative detection of prostate cancer metastases in lymph nodes.

## Key findings

- Fluorescence imaging with OTL78 showed 66.7% sensitivity and 91.7% specificity for detecting metastatic lymph nodes.
- Metastasized lymph nodes had significantly higher fluorescence intensity than benign nodes, confirmed by histopathology and immunohistochemistry.
- No adverse reactions to OTL78 were observed in the six patients tested.

## Abstract

This study aimed to assess the feasibility of intraoperative fluorescence imaging using the PSMA-targeted fluorescent tracer OTL78 for detecting lymph node metastases during pelvic lymph node dissection (PLND) in patients undergoing staging or salvage surgery for prostate cancer.

In a prospective pilot study, six patients scheduled for robot-assisted PLND received a single intravenous infusion of OTL78 at a dose of either 0.06 mg/kg or 0.03 mg/kg, administered 1–2 h prior to surgery. Intraoperatively, lymph node clusters were evaluated using fluorescence imaging. Post-surgical histopathological analysis and immunohistochemistry were performed to confirm tumor presence and PSMA overexpression in fluorescent nodes. The primary outcome was the feasibility of fluorescence imaging in detecting metastatic lymph nodes during PLND.

Fluorescence imaging demonstrated a sensitivity of 66.7% and specificity of 91.7% for identifying metastatic lymph nodes. The positive predictive value was 66.7%, and the negative predictive value was 91.7%. Metastasized lymph nodes (MLN) exhibited significantly higher median fluorescence intensity (MFI) than benign lymph nodes (BLN): 0.51 [IQR 0.11–0.74] vs. 0.06 [IQR 0.03–0.12], p = 0.024. Immunohistochemistry confirmed PSMA overexpression in fluorescent malignant regions. No adverse reactions to the tracer were reported.

Intraoperative fluorescence imaging with the tracer OTL78 is a feasible technique for identifying metastatic lymph nodes during PLND. Fluorescence guidance may assist in detecting small metastatic deposits within nodal clusters that are otherwise difficult to localize. Larger studies are needed to validate these findings and optimize the imaging protocol for broader clinical use.