Measurements of dielectric constants and conductivities of invasive ductal carcinoma (IDC) tissues such as scirrhous carcinoma, solidtubular carcinoma and papillotubular carcinoma were made by use of microwave dielectric spectroscopy. Dielectric constants of inhomogeneous breast tumor tissues were analyzed by use of Bruggeman's effective medium approximation theory. It is found that the dielectric constants of scirrhous carcinoma, solidtubular carcinoma and papillotubular carcinoma of IDC tissues have correlation to the volume fractions of the cancer cells in the stroma tissues.