Chemometric analysis of integrated FTIR and Raman spectra obtained by non-invasive exfoliative cytology for the screening of oral cancer
FTIR spectroscopy and Raman spectroscopy of biological analytes are increasingly explored as screening tools for early detection of cancer. In the present study, an integrated analysis of the FTIR and Raman spectra obtained from exfoliated cells is adopted to improve discrimination of normal, pre-cancerous and cancerous conditions. Multiple spectra were obtained from 13 normal, 13 pre-cancer and 10 cancer patients in both modes. Compared to normal patients, significant differences were observed at 1550, 1580, 1640, 2370, 2330, 2950–3000 and 3650–3750 cm−1 (FTIR) and 520, 640, 785, 827, 850, 935, 1003, 1175, 1311 cm−1 and 1606 cm−1 (Raman) vibrations of the other two. The increase in DNA, protein and lipid content with malignancy was more clearly elucidated by examining both spectra. Principal component analysis (PCA)–linear discriminant analysis (LDA) with 10-fold cross validation of the FTIR and Raman spectral data sets showed efficient discrimination between normal and pathological conditions while overlapping was seen between the two pathologies. The PCA–LDA model of the dual spectra yielded a classification accuracy of 98% in comparison with either FTIR (85%) or Raman (82%) in a spectrum-wise comparison. In the patient-wise approach (mean of all spectra from a patient), the overall classification efficiency was 73%, 80% and 87% for FTIR, Raman and integrated spectral approaches respectively. Moreover, the efficiency of the integrated FTIR–Raman PCA–LDA model as a prediction tool was tested to screen susceptible individuals (11 cigarette smokers) using the dual spectra acquired from these individuals. The study presents proof-of-concept for adopting a large-scale, follow-up trial of the approach for mass screening purposes.