A system is provided comprising an FTIR spectrometer configured to obtain a Fourier Transformed infrared (FTIR) spectrum of a Peripheral Blood Mononuclear Cells (PBMC) sample of the subject; a data processor operable with the FTIR spectrometer, and configured to analyze the infrared (IR) spectrum of the Peripheral Blood Mononuclear Cells (PBMC) sample of the subject by assessing a characteristic of the sample of the subject at at least one wavenumber; and an output unit, configured to generate an output indicative of the presence of a solid tumor, based on the infrared (IR) spectrum. Other embodiments are also provided.