Cancer is a disease of the cells. The body is made up of a community of individual cells, each of which has a specific job to ensure that the community functions correctly. Liver cells must detoxify the fluids of the body, lung cells must exchange oxygen and carbon dioxide from the blood, and skin cells must separate the outside world from the inside of our body. In addition to performing their assigned jobs, cells are also good citizens. Cells respect the space of the other cells around them and support the healthiness of those cells. Occasionally, cells begin to grow in an uncontrolled fashion, causing many problems for the body. Cancer is a disease of uncontrolled cell growth or proliferation. Cancer cells are no longer good citizens. For instance, a liver cell that becomes cancerous no longer does its job of detoxifying the body. In addition, cancer cells do not respect their neighboring cells and will crowd them out of existence. We always had this concept that is still used in pathology today that each cancer type refers to the tissue and cell type of origin. In that case, breast cancers would emerge from the breast cells and have their original characteristics. It turns out that cancer is a combination of many different diseases in one. Cancer is not a single disease, but literally hundreds of different diseases. This is of great practical importance to both physicians and patients, because different cancers have to be treated differently having different outcomes for the patients. In this regard, recent studies have shown that we should classify and also treat tumors mainly based on the mutations that they carry other than the tissue of origin (see more in the article “Mutational landscape and significance across 12 major cancer types” by Kandoth et al. on Nature). Multiple genes are defective in cancers. Cancer does not occur from a single gene mutation in a single gene. Instead, the development of cancer involves multiple mutations within several key genes, including mutations in proto-oncogenes, tumor suppressor genes, DNA repair genes, etc. Researchers recently pointed out that we should start treating tumors based on their genetic and genomic profiles and landscape. These findings lay the groundwork for the development of personalized therapies. In addition, it is clear that pathways of genes should be the focus of treatment (see the comment “Herceptin pioneer’s life science innovation: Cancer pathways should be treatment focus” at MedCity News). These pathways of genes represent the driver defects that could be the cause of the disease, thus providing windows of opportunity in therapeutics (see more in the article “Comprehensive identification of mutational cancer driver genes across 12 tumor types” by Tamborero et al. on Nature). In the future, cancer will be a chronic disease controlled by an array of medicines each targeting a defective pathway of that specific tumor. Cancers will soon be classified based on their genetic profiles instead of the tissue of origin. Drug companies are already starting to adapt to this trend and new cocktails of more targeted therapies are on the horizon (Image Source: FOX News).