Cancer cell experiments fall flat at the bottom of a Petri dish. This image shows three spherical clusters of cancer cells (blue/white dots) implanted in a three-dimensional matrix of protein fibers (white strands).

These tiny tumors allow researchers to understand how small metastases interact with their surrounding environment, and to evaluate the delivery of drug-loaded nanoparticles. The use of spheroids rather than isolated cells offers a more well-rounded picture of the challenges researchers must overcome to detect and treat cancer.