Infrared spectroscopy of normal and abnormal cervical smears: evaluation by principal component analysis

Fourier-transform infrared (FT-IR) spectra of malignant and dysplastic cervical scrapings were abnormal, as first described in our study of a limited number of samples, where the spectra were evaluated by visual inspection and peak intensity ratios. We have expanded our study to evaluate more cervical conditions, and to analyze the spectra by a chemometric approach (principal component analysis [PCA]). Cervical samples from 436 females were evaluated by FT-IR and Papanicolaou testing; 40/436 spectra were nonanalyzable. The remaining were as follows: normal, 174; malignant, 19; dysplasia, 8; atypia, 113; atrophy, 19; inflammatory, 47; bloody smear, 12; hypocellular, 4. PCA analysis followed by chi2 test revealed that statistically significant frequencies of being predicted malignant by FT-IR were associated with samples diagnosed as malignant (P < 0.0001), and also those diagnosed as "atrophy" (P < 0.001), "atypical with bloody smear" (P < 0.05), "atypical with atrophic pattern" (P < 0.05), and "dysplasia" (P < 0.05). Based on these findings, for the diagnosis of cervical cancer by FT-IR, as defined here, the sensitivity is 79%, the specificity is 77%, the positive predictive value is 15%, and the negative predictive value is 98.6%. Our findings (a) demonstrate the application of a chemometric approach to the study of cervical FT-IR spectra; (b) assess its potential diagnostic role; (c) suggest that atrophic and neoplastic samples share structural features; and (d) suggest that blood may interfere with such spectroscopic evaluation. These findings warrant further evaluation of FT- IR spectroscopy in cervical and other malignancies.