In a general sense, cancer cells are driven by the same, unifying goal to grow and divide. However, after enough growing and dividing, a tiny minority of those cells bucks the trend and does something different, metastasize.
Metastasis is complex and still largely unknown.
Cells have to go through myriad changes as they traverse the path from their original home in the primary tumor to new tumors they seed and form throughout the body.
The cells change from stationary to mobile, actively pushing their way out of their tumor home. These cells breech the walls of blood vessels or lymph nodes. They survive the strange new environment and physical forces of the circulatory system. Once they reach their final destination, they do all these steps in reverse and trigger the growth of a metastatic tumor.
Metastasis is inefficient.
Some large tumors may shed upward of a million cells into the bloodstream every day, but only a few of these cells actually form new metastatic tumors.
According to the American Cancer Society, nearly all deaths from solid tumor cancers are due to metastatic disease.
Unfortunately, even now, there is still a lot that researchers don’t understand about the process or how to stop it. The more they learn about metastasis, the more questions they add to the list of outstanding questions.
Sometimes, metastatic cells are disbursed throughout the body before a patient’s primary tumor is diagnosed. About 5% of patients with metastatic cancer have unknown primary which means their doctors can’t figure out where the cancer started, because the primary tumor wasn’t detected before it started spreading.
This points to the importance of screening and early detection. Unfortunately, metastasis can begin even when the primary tumor is not even detectable. Researchers have seen that the cells shed from these tiny tumors are better at spreading and seeding new metastatic tumors.
Researchers believe that new therapies to prevent or treat metastasis need to focus on the biology of the cells that spread before the primary tumor is detectable.