In cancer parlance, metastasize is a four-letter word. Metastasis is
when cancer cells break off of the primary tumor to surf the bloodstream
and set up shop in new organs and body areas. Thankfully, researchers
are developing a new way to combat this life-and-death variety of
hide-and-go-seek, a strategy borrowed from one of the best dang seekers
around—the Google PageRank algorithm.

To start, researchers gathered data from the autopsy reports of lung
cancer patients from 1914-1943. The time period is important because it
predates interventions like radiation and chemotherapy, which allowed
the study to look at cancer left to its own jerky devices. The
researchers could then load the many real-life cancer trajectories into
“an algorithm similar to Google PageRank … to gain important insights
about the spread patterns of lung cancer,” as a press release put it.
The findings were published recently in Cancer Research.

“Basically, we are doing the inverse of what Google does,” says Paul
Newton, an applied mathematics specialist at USC Viterbi School of
Engineering. “They know the transition probabilities and compute the
steady-state, we know the steady-state and compute the transition
probabilities.”

In other words, Google knows where you could go and uses a
mathematical system called Markov chains to determine how likely you are
to get there. The researchers knew where cancer did go and used similar
equations to investigate how it got there. (It won’t surprise anyone in
the math crowd that Google PageRank is based on these Markov chains, or
sequences of random variables used to determine the probability of
going from one “state” to another. But the analogy is a deft move by the
Scripps PR department as most of our ears do not exactly prick at the
mention of algorithms, statistical models, or transition probabilities.)

Newton and his team have also used this sophisticated system of
mathematical equations to identify certain regions of the body that work
as “sponges” and “spreaders.” For instance, lung cancer cells often
travel to sponge sites like the liver, lymph nodes, and bones, but
generally don’t branch out further from these posts. Conversely, the
kidneys and adrenal gland seem to be spreaders, veritable launch pads
for later stages of invasion.

This research calls into question the prevailing theory that
metastatic lung cancer marches in one direction. Even more interesting,
by identifying sponges and spreaders, the researchers may have given us a
new way to target treatments and lessen or prevent the spread of
cancer. If we could learn more biologically about what makes a sponge a
sponge, perhaps we could alter these parts of the body to perform that
function even better. Newton described this to me colorfully as a “Hotel
California,” a place where “a circulating cancer cell enters but never
leaves.”

As for spreader sites, we may one day have the option to jettison
organs we can do without. Obviously, this works better for viscera like
kidneys than it does for, say, bones.

Let’s get this clear: We’re not going to cure cancer by logging into
Google Analytics. But this research is important because it shows how
cancer’s movement is not unlike the spread of information, a topic we
know quite a bit about. It also illustrates some of the intriguing
possibilities coming out of recent partnerships between oncology and the
physical sciences. (The study was sponsored by the National Cancer
Institute’s initiative to create a dozen new Physical Sciences Oncology
Centers.)

If you’re one of the 1.6 million Americans expected to be diagnosed
with cancer this year, it might make you feel a wee bit better to know
that not only are we doing clinical trials on every-freaking-thing we
can think of—but now mathematicians like Newton are utilizing Markov
chain models to root out tumors using computer simulations based on
force/mass/acceleration equations of motion.

“Computer simulations and models will never take the place of
clinical trials,” says Newton, “but it certainly would be useful to be
able to design trials so that they have optimal bang-for-buck impact.”

One thing is certain, cancer is slippery. We’ve been stabbing it with
steely knives since the second century, and yet we just can’t kill the
beast. But if Google can be trusted to wrangle some trillion pieces of
Web, perhaps we can use that math for something other than ranking chili
recipes.

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