Practical World True News Magazine

Practical World True News Magazine
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Practical World True News Magazine

Most Cancer Is Beyond Your Control, Breakthrough Study Finds

Most Cancer Is Beyond Your Control, Breakthrough Study Finds



There’s a lot we can do to protect ourselves from certain cancers — don’t
smoke, avoid prolonged exposure to the sun, and try not to breathe or ingest too
many chemical pollutants in the air or our food. But scientists have always
known that this was only part of the cancer story. There’s also heredity, but
that only explains about 5% to 10% of cancer. The truth of the matter is that
some tumors emerge simply at random. But how much of malignancy can be
attributed to this unfortunate roll of the dice? What really causes cancer?

Christian Tomasetti and Bert Vogelstein at Johns Hopkins University believe
they may have found an answer, and it’s likely to turn our understanding of
cancer — and how it should be diagnosed and treated — on its head. In a groundbreaking paper published in Science, the duo
describe a new factor, a tissue’s stem cells, that may explain as much as
two-thirds of the difference in cancer risk among different tissues.

Many tissues in the body have stem cells, or feeder cells that serve as
factories for churning out more cells of the same kind; it’s what keeps our skin
cells refreshed, and our blood and immune cells young and vigorous. This
replicative power is the engine that keeps the body going, allowing tissues to
replace cells as they die off. But it’s also the process behind cancer, since
cancer is caused by cells that pick up mutations in their DNA when they divide —
and stem cells are the only population that copy their DNA and divideto make
more cells. Only a small proportion of a tissue’s cells are made up of stem
cells, so Tomasetti and Vogelstein decided to map out whether the number of stem
cells a specific tissue has bears any relationship to its tendency to develop
cancer.

MORE: Promising New Cancer Treatment Uses Immune
Cells


Indeed, when they charted out the stem cell data for 31 types of tissues,
they found a dramatic connection between the two — the more stem cells the
tissue had, the higher its incidence of cancer over a person’s life time on
average. “Think of cancer as the risk of having an accident if you are driving a
car,” says Tomasetti, a biostatistician who holds positions in the department of
oncology at Johns Hopkins Kimmel Cancer Center and the Johns Hopkins Bloomberg
School of Public Health. “If you drive the car on a cross country trip, your
risk of an accident is much higher than if you take a local trip to the grocery
store. The risk correlates to the length of the trip. The trip to the grocery
store might be thought of as bone cancer, which has few stem cell divisions.
While the cross country trip might be more like colon cancer, which has many
more cell divisions.”

In fact, the correlation held strong among cancers that were both common and
more rare. The more likely those cells would divide and develop DNA errors or
mutations in the process that led to uncontrolled growth, the more likely that
tissue would develop tumors.

“It was quite surprising to us. We think it’s pretty big,” he says. “About
65% of cancer incidence across tissue types appears to be explained by the
number of stem cell divisions.”

MORE: Stem Cells That Kill

Having a detailed understanding of both how large a tissue’s stem cell
population is, as well as how active it is, could be a determining factor in
whether it’s likely to develop cancer. Both the brain cells that can cause
glioblastoma and medulloblastoma, and the colon contain about the same number of
stem cells, Tomasetti estimates — about one hundred million. But the colon stem
cells divide about 6000 times on average during lifetime, compared to nearly
zero for the brain stem cells. That leads to rates of colon cancer that are 22
times higher than rates of the brain tumors.

Print

Credit: C. Tomasetti, B. Vogelstein and illustrator
Elizabeth Cook, Johns Hopkins


Such an explanation could also resolve some of cancer’s mysteries — why
people who don’t smoke still get lung cancer in surprising numbers, or why rates
of colon cancer are higher than rates of cancer in the small intestine, despite
being shorter in length. One reason, says Tomasetti, could have to do with the
different stem cell activity in these tissues.

This finding potentially changes the landscape of cancer. In recent decades,
cancer rates have come down due to aggressive efforts to educate and motivate
people to take positive steps toward preventing cancer in the first place, such
as quitting smoking and avoiding the sun’s ultraviolet rays. Have those messages
been wrong?

Not exactly. Tomasetti says that the study shows that it’s time to redirect
that cancer strategy a bit — not abandon it. For example, he and Vogelstein
propose looking at cancers in two categories, those that are primarily due to
genetic bad luck, and those that are due to that unfortunate roll of the genetic
dice plus environmental or hereditary factors. So melanoma, ovarian cancer, many
brain cancers, lung cancer among non-smokers, the most common leukemias and bone
cancers, for example, are pretty much out of people’s control. They’re the
result of the random mutations caused by the stem cells dividing in these
tissues — bone, blood, ovaries, brain and skin — that make mistakes that turn
malignant. For these cancers, changing your lifestyle or trying other
interventions to stop the cancer from occurring in the first place won’t help.
But being vigilant about screening, and picking up the first signs of trouble
early, can be life saving.

For the other type of cancers, those that are the product of both stem cell
mutations and heredity or other exposures, continuing with proven prevention
methods, which include screening in cases of inherited disease, as well as
quitting smoking and reducing exposure to radiation and carcinogens, is still
critical. That’s what has lowered rates of lung cancer among smokers, for
example, and colon cancer among those with hereditary disease.

“Everything we know about altering lifestyles to prevent cancer from the
environmental point of view we absolutely need to continue doing,” says
Tomasetti. “If anything it puts more stress on the need to spend even more money
on early detection. It may be the key tool for quite a few cancer types.”

Tomasetti admits that two common cancers are missing from the study — breast
cancer and prostate cancer. That’s because knowledge about their stem cell
populations, and how often those tissues renew, isn’t quite as solid as it is
for tissues such as colon. “We are working on that,” he says. “We hope this type
of work highlighting the importance of self renewal will cause others to
investigate these stem cell populations in more detail as well.”




















In the meantime, he stresses that while we may not be able to prevent the
tumors from forming, it’s still possible to treat them and potentially save
lives by finding them early and removing them or using chemotherapy or radiation
to keep them under control. “My biggest fear is that people will say forget
about it, and then do nothing. The opposite is true. We need to do everything we
did before, but we want to do it even more than before,” he says.
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