Tumor cells from a variety of cancers commonly metastasize to the bone. Work in our laboratory has shown that these nasty cellular invaders displace the normal resident bone marrow stem cells from their home or “niche”. The niche provides a specialized environment that keeps bone marrow stem cells (or the invading tumor cells) dormant for long periods of time. A better understanding of how tumor cells invade the marrow and compete for these niches could lead to new therapies to prevent tumor metastasis. In the study shown here, we have made artificial bone marrow niches so that we can study invasion under controlled conditions. This photo depicts the initial phases of bone formation in a sponge matrix. Remnants of the sponge are bright turquoise blue, surrounded by forming bony tissue of dark green and blue.