In vivo Raman spectroscopy: monitoring cancer progression post carcinogen withdrawal

Studies investigating relationship between tobacco withdrawal/discontinuation (tobacco-quitting habit) and risk of cancer-progression are usually retrospective. Hamster-buccal-pouch (HBP) develops tumors in 14 weeks on topical-application (painting) of carcinogen 7,12-Dimethylbenz[a]anthracene (DMBA). In this study HBP model was employed to investigate cancer-progression post 8-week-DMBA-application employing in vivo Raman spectroscopy (RS). 20 animals (6-8 weeks) were randomized into 4 sets; spectra were acquired at the end of 0, 8 and 14 weeks from each animal. Set1: DMBA-painting was carried out for 14-weeks. Set2: DMBA-painting was discontinued after 8-weeks of painting (analogous to tobacco-quitting). Set 3: Vehicle control-only vehicle was applied. Set 4: Independent set of animals with DMBA-painting for 14-weeks; to compare spectra from sets 1-3. DMBA painting involved application of 0.5% DMBA dissolved in vegetable oil (vehicle). Multivariate analysis revealed cancer-progression in spectra from 8 and 14 weeks of continuous DMBA-painting however, in case of DMBA painting discontinued after 8 weeks, but spectra acquired after 14 weeks, only 28% spectra classified with tumors. Visible tumours were not observed but histopathological evaluation suggested higher pathologies (carcinoma-in-situ) in Set 2 animals. Observations suggest a cause-and-consequence effect between DMBA-discontinuation and reduced cancer-progression over a defined time-period. Findings can be extrapolated to tobacco habitues to suggest reduced risk of cancer progression on quitting primary consumption of tobacco. Findings further suggest RS as a prospective label-free and noninvasive candidate tool to screen risk-prone population.