Recent advances in cancer biology have shown that a tumor is not a uniform mass. It consists of many different cancer cells and is embedded in an environment of immune cells, connective tissue and blood vessels. This variety is a significant factor in determining whether a tumor spreads and how well a therapy works. While single-cell approaches are considered pioneering instruments in cancer research, their translation into clinical practice has been limited to date, primarily due to a lack of large patient data sets with comprehensive clinical histories.