Seed or soil?
When and why cancers spread (metastasize) are subjects of intense investigation. We know cells frequently escape from most cancers, including lung cancer, resulting in the dissemination of malignant cells into the blood stream on a regular basis. However, a cancer can be present for variable lengths of time, sometimes even years, before a metastasis forms in a distant organ. One may never develop. Is the reason for this erratic behavior because only some of these circulating cells have the potential to survive unattached to the primary tumor? Or alternatively is the key that they must find themselves in an organ capable of providing the right environment to nurture them to settle in and thrive? After all, metastases are more likely to be found in some organs, such as the liver, than in others such as the kidney.
As the problem is frequently stated, is the difference maker the seed or the soil? If we understood this biological process then it might be possible either to prevent metastases from developing or eradicate them once they have been detected. We do know that as a lung cancer enlarges it is more likely to metastasize but small ones can metastasize and large ones not. This aspect of the behavior of cancer remains a mystery.
