Rapid volumetric growth and extensive invasion into brain parenchyma are hallmarks of
malignant neuroepithelial tumors in vivo. Little is known, however, about the mechanical impact
of the growing brain tumor on its microenvironment. To better understand the environmental
mechanical response, we used multi-particle tracking and microrheological methods to probe the
environment of a dynamically expanding, multicellular brain tumor spheroid that grew for six
days in a three-dimensional Matrigel-based in vitro assay containing 1.0 mm latex beads. These
beads act as reference markers for the gel, allowing us to image the spatial displacement of the
tumor environment using high-resolution timelapse video-microscopy. The results show that the
volumetrically expanding tumor spheroid pushes the gel outward and that this tumor-generated
pressure propagates to a distance greater than the initial radius of the tumor spheroid.
Intriguingly, beads near the tips of invasive cells are displaced inward, towards the advancing
invasive cells. Furthermore, this localized cell traction correlates with a marked increase in total
invasion area over the observation period. This case study presents evidence that an expanding
microscopic tumor system exerts both significant mechanical pressure and significant traction on
its microenvironment.