The development of cancer involves a multi-tiered, intricate, erratic process that, frankly from a cellular perspective, is a very rare occurrence. As outlined in the hallmarks of cancer, for normal cells to transition to cancerous cells, and then develop into malignant tumors, requires acquisition of a unique set of many specialized traits. Only the most aggressively growing and somewhat carelessly replicating cells have a chance at finding the right combination of multiple mutations needed to survive. Basically, cancer cells are in an evolutionary race to grow, reproduce, and acquire the characteristics to thrive in the hostile environment of the body which kills off abnormal cells. As a result, by the time a tumor forms, rapid evolution has generated a diverse population of cells. Recent studies from Stanford and Massachusetts General Hospital demonstrate this cell diversity in single cancer.
Researchers in the Stanford study published on May 7 in PLoS ONE used a magnetic filter to isolate circulating tumor cells from 20 breast cancer patients, then a microfluidic approach to analyze which genes are expressed in individual cells. They found that the cells did "not cluster by patient or disease stage," which means that there more difference in the cells found in a single patient than cells between patients, and each cell was very different from the average profile seen with a whole tumor. Also, less than 10% of the cells had similar profiles as cell line models typically used in the lab for experiments and drug screening.
The Mass. General study in the May 15 issue of Cancer Cell, looked at how labeled tumor cells in zebrafish invade and colonize other parts of the fish to produce new tumors. They found that certain cells that don't replicate well first find a new site for a tumor and seem to prepare an environment, and then slower moving cells that reproduce rapidly settle into the same site and start tumor growth. It seems that different cancer cells have different functions, such as migration and colonization vs. reproduction, and this division of labor, with specialized cells playing various roles in cancer biology, is likely a general feature of cancer cell populations.