In some ways, cancer is maddeningly uniform. Different cells in a tumor aren’t all identical, but in a general sense, they are driven by the same, unifying goal: grow and divide, grow and divide, grow and divide. But one day, after enough growing and dividing, a tiny minority of those cells bucks the trend and does something different.
They metastasize.
Metastasis, or cancer spread, is complex and still largely mysterious. Those maverick 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.
They change from stationary to mobile, actively pushing their way out of their tumor home. They breech the walls of blood vessels or lymph nodes. They survive the strange new environment and physical forces of the circulatory system. And at their final destination, they do all these steps again in reverse, setting up shop anew and triggering the growth of a metastatic tumor.
Metastasis is very 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. If it weren’t so deadly the feat of those few cells would be almost awe-inspiring — nearly all deaths from solid tumor cancers are due to metastatic disease, according to the American Cancer Society.
Even so, there’s still a ton researchers don’t understand about the process, let alone how to stop it, said Fred Hutchinson Cancer Research Center postdoctoral fellow Dr. Minna Roh-Johnson, who studies the biology of melanoma metastasis.
“The more I learn about metastasis from my work and other people’s work, the more outstanding questions I feel like get added to the list of outstanding questions,” she said. “Almost every step is an unknown.”
Step one: First steps
Step two: Breaking barriers and surviving torrents
Step three: Finding a new home
Step four: Waking up
It’s not clear why some metastatic cells stay dormant for so long while others wake up relatively soon after spreading. About one in five metastatic breast cancer patients won’t get metastases until 10 years after they’ve been treated, Ghajar said.“You can imagine how crushing that is,” he said. “It’s crushing across the board, but you go 10 years after treatment, you think you’re cured, and all of a sudden you have a relapse.”....
