Biochemical imaging and 2D classification of keratin pearl structures in oral squamous cell carcinoma

Precise regulation of cell organization results in well-differentiated tissue structures and continuous renewal of the oral epithelium maintaining a highly ordered tissue architecture. Here we demonstrate that FT-IR microspectroscopy, performed on sections of cancerous tissue biopsies, is capable of generating biochemical maps that show the distribution and any abnormal concentration of individual classes of biomolecules. Oral epithelia affected by cancer (squamous cell carcinoma) show many abnormal changes in morphology, of which the formation of keratin pearls is only one. Spectra from selected pearl areas demonstrate that these structures contain not only abnormal keratin concentrations but also seem to be stabilized by surrounding collagen fibers. Infrared image maps reveal that in the center of keratin pearls the concentration of protein (cytokeratins) is abnormally high, that DNA is absent and that the cell membrane fluidity is reduced. This suggests that cells are structurally destroyed and transformed into nuclei-free horny cells, simulating normal differentiation and epithelial growth. We also introduce a new analysis modality, two-dimensional (2D) tissue classification, and apply it to establish spectral similarities between different tissue structures. A total of 315 spectra, recorded for the original map, were analyzed by pattern recognition methods, classified and re-assembled into new maps based on their spectral similarities. The re-assembled maps clearly indicate significant tissue changes outside the pearls, suggesting early biochemical changes that accompany abnormal growth. Employing this 2D analysis modality in combination with infrared histopathology may be relevant to tumor diagnosis and prognosis.