Cancer arrases as normal cells accumulate mutations. Most of the time cells can detect mutations or DNA damage and either fix them or self destruct. Some mutations allow cancerous cells to grow unchecked and invade near by tissues, or even metastasize to distant organs. Cancers become almost incurable once they metastasize and cancer is incredibly complex. Its not just one disease, There are more than 100 different types and we don’t have a magic bullet that can cure all of them.
For most cancers, treatments usually include a combination of surgery to remove tumors and radiation and chemo therapy. To kill any cancerous cells left behind Hormone therapy immunotherapy, and targeted treatments tailored for a specific type of cancer are sometimes used too. In many cases these treatments are effective and the patient becomes cancer free.
Most cancer treatment are developed using cell lines grown in labs from cultures of human tumors. These cultured cells have given us critical insights about cancer genetics and biology but they lack much of the complexity of a tumor in an actual living organisms. Its frequently the case that new drugs, which work on these lab grown cells will fail in clinical trials with real patients. One of the complexities of aggressive tumors is that they can have multiple populations of slightly different cancerous cells. Over time, distinct genetic mutations accumulate in cells in different parts of the tumor, giving rise to unique sub clones.