LB5 - Clinical Value of Carbon Nanoparticle Staining in Identifying Metastatic Lymph Nodes in Colorectal Cancer Surgery

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Purpose/Background: Carbon nanoparticles (CNPs) are increasingly used to trace lymph nodes (LNs) in colorectal cancer (CRC) surgery. However, the relationship between CNP-stained LNs and metastatic LNs remains unclear. Whether CNPs can guide lymph node dissection also needs to be addressed. This study aimed to evaluate the clinical utility of CNP in identifying metastatic LNs by analyzing each LN from different regional groups in CRC surgery.

Methods/Interventions: A total of 146 patients with colorectal cancer were enrolled between January 2022 and March 2024. Perioperatively, using the “Sandwich” technique, 0.5 ml of carbon nanoparticle (CNP) suspension was injected into the submucosal layer at the lower margin of the tumor. The injection was administered in a sequence of 1 ml of normal saline, followed by 2.5 ml of CNP suspension (comprising 0.5 ml CNP and 2 ml normal saline), and concluded with another 1 ml of normal saline. All patients subsequently underwent laparoscopic or robotic radical resection with D3 LNs dissection. LNs were dissected and harvested according to clinical guidelines. Each LN from three regional groups—pericolic/perirectal (D1 region), intermediate (D2 region), and main LNs (D3 region)—was separately analyzed. The identification of stained and non-stained LNs was confirmed by microscopic observation.

Results/Outcomes: Of 146 patients, 39.0% had stage I tumors, 28.1% had stage II, 24.7% had stage III, and 8.2% had stage IV. The tumor locations are predominantly in the rectum and sigmoid colon. A total of 3212 LNs were retrieved, of which 423 (13.2%) were not stained by CNP, predominantly in the D1 region (79.7%). Significantly more metastatic LNs were detected in non-stained LNs compared to stained LNs (11.9% vs. 3%, p < 0.001). Among 32 retroperitoneal LNs collected, 5 metastatic LNs were identified in 7 non-stained LNs (71.4%), whereas no metastatic LNs were found in the stained group.

Conclusion/Discussion: CNP staining does not enhance the identification of metastatic LNs. Non-stained LNs should be more vigilantly assessed for metastasis. The frequent non-staining of metastatic LNs may be attributed to the hypothesis that tumor cells infiltrate and occupy the space within lymph nodes or lymphatic vessels. This infiltration could impede the flow of CNPs and the migration of macrophages, thereby preventing effective staining. Despite this, CNP injection remains a feasible and safe method for LN tracing, which can aid in tumor immunology research.