Mechanics of cancer cells are directly linked to their metastatic potential, or ability to produce a secondary tumor at a distant site. Metastatic cells survive in the circulatory system in a non-adherent state, and can squeeze through barriers in the body. Such considerable structural changes in cells rely on rapid remodeling of internal structure and mechanics. While external mechanical measurements have demonstrated enhanced pliability of cancer cells with increased metastatic potential, little is known about dynamics of their interior and we expect that to change significantly in metastatic cells. We perform a comparative study, using particle-tracking to evaluate the intracellular mechanics of living epithelial breast cells with varying invasiveness. Particles in all examined cell lines exhibit super-diffusion with a scaling exponent of 1.4 at short lag times, likely related to active transport by fluctuating microtubules and their associated molecular motors. Specifics of probe-particle transport differ between the cell types, depending on the cytoskeleton network-structure and interactions with it. Our study shows that the internal microenvironment of the highly metastatic cells evaluated here is more pliable and their cytoskeleton is less dense than the poorly metastatic and benign cells. We thus reveal intracellular structure and mechanics that can support the unique function and invasive capabilities of highly metastatic cells.