Minimally invasive laser-induced thermotherapy (LITT) presents an alternative method to conventional tumor therapeutically interventions, such as surgery, chemotherapy, radiotherapy or nuclear medicine. Optical tissue characteristics of tumor cells and their heat-induced changes are essential issues for controlling LITT progressions. Therefore, it is indispensable to exactly know the absorption coefficient μ a , the scattering coefficient μ s and the anisotropy factor g as well as their changes under rising temperatures in order to simulate the treatment parameters successfully. Optical parameters of two different cancer model tissues -breast cancer cells species MX1 and colon cancer cells species CX1 -were measured in the spectral range 400 -1100 nm as well as in the temperature range 37 -60• C. The absorption coefficient of both cell species was low throughout the spectral range analyzed, while μ s of both species rose with increasing temperatures. The anisotropy factor g however dropped for both tissues with increasing temperatures. Light scatterings inside tissues proceeded continuously forward for all species tested. It was demonstrated that optical tissue properties undergo significant changes along with the vital status of the cells when the temperature increases. Screening of the metabolic activities of MX1 and CX1 cells after exposure to heat stress