We assess the feasibility of our developed quantitative thermoacoustic tomography (qTAT) system for breast tumor characterization using mastectomy specimens before the clinical investigation.A circular scanning TAT system coupled with a finite-element based reconstruction algorithm is used to recover the dielectric property distribution of normal and tumor tissues from three female subjects who underwent mastectomy.Statistical method is used to analyze the tissue dielectric properties obtained.The recovered qTAT images reveal large contrast in conductivity between tumor and normal breast tissues.In addition,significant difference in conductivity exists among all the specimens examined.Finally,the recovered tumor size for these specimens agrees well with their exact size.This preclinical evaluation suggests that it is feasible to detect and characterize a breast tumor quantitatively with our qTAT method.