Three-way multiplexing in prostate cancer patients — combining a bimodal sentinel node tracer with multicolor fluorescence imaging

We present images from a 71-year-old prostate cancer patient who underwent a robot-assisted radical prostatectomy and extended pelvic lymph node dissection (ePLND) comple-mented with experimental sentinel node (SN) resection [1]. Additional intraoperative lymphangiography was performed to highlight lymphatic structures that should ideally be spared. This concept is part of a prospective trial wherein we aim to use the presented approach to reduce the 20% complication rate associated with ePLND procedures [2].

We present images from a 71-year-old prostate cancer patient who underwent a robot-assisted radical prostatectomy and extended pelvic lymph node dissection (ePLND) complemented with experimental sentinel node (SN) resection [1]. Additional intraoperative lymphangiography was performed to highlight lymphatic structures that should ideally be spared. This concept is part of a prospective trial wherein we aim to use the presented approach to reduce the 20% complication rate associated with ePLND procedures [2].
For SN identification, the bimodal/hybrid tracer ICG-99m Tcnanoscan (218 MBq in 2 ml) was used, which has replaced the well-known ICG-99m Tc-nanocolloid [3]. Preoperative (lymphoscintigraphy and SPECT/CT) and intraoperative SN imaging (gamma and fluorescence imaging) were performed after intraprostatic tracer injection. Previous work indicates that the hybrid tracer and the visible-dye fluorescein both stain lymphatic structures, but with different kinetics [4]. It is also known that multi-color fluorescence imaging can be used to differentiate between lymphatics of different organs [5,6]. With this first-in-human implementation (see Scheme), we underscore that lymphatic ducts draining the left upper leg can be made visible using fluorescein (80 mg in 4 ml; yellow, dotted triangle) and that this drainage can be distinguished from the SNs visualized with ICG-99m Tc-nanoscan (blue, dotted circle). With that, the former can act as "red-flag" to highlight tissues that should be spared, while the latter provides a "green-flag" for tissues that should be resected. As such, the presented threeway multiplexing approach may help preserve the oncological benefit of ePLND + SN [3], while providing a handle to reduce complication rates.
Author contribution All authors contributed to the study conceptualization and design. Material preparation was performed by ACB, FvL, and TB. Data collection and analysis were performed by ACB, TB, MNvO, LS, and HGvdP. All authors read and approved the final manuscript.
Funding This work was financially supported by an NWO-TTW-VICI (TTW BGT16141) grant.

Declarations
Ethical approval All procedures performed in this study were in accordance with the ethical standards of the local ethics committee of The Netherlands Cancer Institute -Antoni van Leeuwenhoek Hospital (NL78523.031.21, N21SPL, NCT05120973) and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards.

Consent for publication
The authors affirm that written informed consent was obtained from all patients prior to inclusion in this study.

Conflict of interest The authors declare no competing interests.
Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http:// creat iveco mmons. org/ licen ses/ by/4. 0/.