Raman endoscopy a robust tool for real-time in vivo NPC staging

Raman spectroscopy may be a clinically powerful diagnostic tool for real-time in vivo staging of nasopharyngeal cancer (NPC) during endoscopy, a study from Singapore has shown.

“[The study] demonstrated correlative primary NPC Raman spectral differences across NPC staging, confirming biomolecular sensitivity of the fibreoptic Raman spectroscopy for differentiating NPC stages,” said the researchers.

Measurements were taken using the fingerprint/high-wavenumber (FP/HW) fibreoptic Raman spectroscopy system on 61 newly diagnosed NPC patients and 50 healthy volunteers (normal cohort) at the National University Hospital Head and Neck Clinic. Thirty-six NPC patients had stage IV disease. [Talanta 2023;doi:10.1016/j.talanta.2023.124561]

Of the 278 tissue sites, 86 were from the normal cohort, while the rest were obtained from the NPC group (n=21, 13, 46, and 112 for stages I, II, III and IV, respectively). A total of 5,205 Raman spectra were obtained from normal (n=1,602) and NPC tissues (n=422, 308, 784, and 2,089 [stages I, II, III, and IV]).

Signature tissue Raman peaks of NP tissues were clearly identified in both FP (853, 875, 940, 1,004, 1,078, 1,209, 1,265, 1,335, 1,445, 1,554, and 1,665 cm^-1) and HW regions (2,850, 2,885, 2,940, and ~3250 to ~3400 cm^-1).

There were significant Raman spectral differences (p<1×10^-5) in multiple Raman peaks in both FP and HW regions (eg, 853, 875, 940, 1,004, 1,078, 1,209, 1,554, and 2,940 cm^-1), signalling significant biomolecular differences between normal nasopharynx and NPC at different stages.

Normal patients had markedly lower protein-to-lipid ratio than NPC patients regardless of cancer stage (p<0.001), providing evidence of biomolecular changes in protein and lipid contents in malignant NP tissues.

There was also a significantly decreasing trend in protein-to-lipid ratio from early- to late-stage NPC (p<0.01), suggesting the possibility of higher lipid accumulation levels in late-stage NPC and validating the biomolecular tumour microenvironment in locally advanced NPC, the researchers noted.

Overall diagnostic accuracy was 92.81 percent for identifying different NPC stages from a normal nasopharynx. Diagnostic sensitivity was 91.18 percent for identifying NPC stages I & II and 93.04 percent for NPC stages III & IV.

Accurate cancer staging is essential

NPC prognosis depends upon disease stage. [BMC Cancer 2018;18:606] “Therefore, it is crucial to accurately stage NPC patients in a timely manner to facilitate and standardize prognosis evaluation and treatment management,” said the researchers.

Currently, the most commonly used staging system for NPC is the tumour-node-metastasis (TNM) system. [Cancer 2016;122:546-558; J Cancer 2017;8:1665-1672] Accurate TNM staging requires a thorough assessment of anatomical prognostic information, including physical exam, nasopharyngoscopy, and head and neck MRI.

“[However, this] is highly limited by the sensitivity of imaging modalities. Consequently, periodic revisions and modifications based on clinical imaging and modalities development are required to refine the current clinical TNM staging system,” they continued.

“Therefore, it is of high interest to uncover non-anatomical prognostic factors that could reflect NPC tumour behaviour for a more accurate and objective NPC tumour staging,” they added. “The development of a rapid and accurate NPC staging system using non-anatomical prognostic information is highly desirable for real-time clinical management and prognostication.”

The Raman-based staging technique was faster and cost-effective compared with the current NPC staging protocol, with molecular specificity for label-free, real-time in vivo staging during endoscopy.

“With the ability of biochemical specificity, fibreoptic Raman endoscopy can be used to probe biomolecular prognostic factors, enabling prognostic evaluation of NPC patients in real time at molecular level,” said the researchers.

A larger, multicentre study is underway to further explore the clinical merits of accurate staging of NPC patients for more effective head and neck cancer management.