SPIE Proceedings [SPIE Saratov Fall Meeting 2015 - Saratov, Russian Federation (Tuesday 22 September 2015)] Saratov Fall Meeting 2015: Third International Symposium on Optics and Biophotonics and Seventh Finnish-Russian Photonics and Laser Symposium (PALS) - Physico-chemical and biochemical approaches to assessing the development of precancerous pathologies of the gastrointestinal tract during their modeling in mice with complex effects of stress factors of different nature