Jan. 5, 2016 / 2:16 PM
CST / Updated Jan. 5, 2016 / 2:15 PM CST
By Maggie Fox
About a
third of all cancer cases can be blamed on inherited genes, a giant study
finds.
It’s
the biggest and longest study yet done to examine the family links to cancer
and it finds that certain types of cancer seem to have very strong genetic
links — testicular cancer and melanoma, especially.
The
overall findings are not a big surprise. They support earlier findings that
show about a third of all cancer cases can be blamed on faulty genes. Most of
the rest are due to so-called lifestyle factors such as smoking, diet and
exercise.
What is
new is the variation in inherited risk by cancer type. About 58 percent of
melanoma cases, 57 percent of prostate cancer cases and 39 percent of ovarian
cancer appear to come down to inheritance.
Kidney
cancer is linked to family inheritance about 38 percent of the time, breast
cancer 31 percent of the time and uterine cancer 27 percent of the time, the
team reports in the Journal of the American Medical Association.
The
group, led by Lorelei Mucci, of the Harvard T.H. Chan School of Public Health,
looked at the medical records of more than 200,000 twins, both identical and
fraternal, born in Denmark, Finland, Norway, and Sweden between 1943 and 2010.
They
have been followed for an average of 32 years.
Teasing
out the differences between identical and fraternal twins is a time-honored way
of differentiating between inherited, genetic influences and other factors,
such as a shared environment. Identical twins share all their genes while
fraternal twins are as genetically alike as any other siblings. So differences
in cancer rates between the groups point very strongly to genetic factors.
Cancer
was diagnosed in 38 percent of the identical twins and 26 percent of the
fraternal twins, Mucci’s team found. So when one fraternal twin was diagnosed
with any type of cancer, his or her twin had a 37 percent risk of getting
cancer, too. But for identical twins, the risk was 46 percent.
“Because
of this study’s size and long follow-up, we can now see key genetic effects for
many cancers,” said Jacob Hjelmborg of the University of Southern Denmark, who
helped lead the study.
"We
can now see key genetic effects for many cancers."
Testicular
cancer appeared to have a very high inherited risk. A man’s risk for cancer of
the testicle was 12 times higher if his fraternal twin had it but 28 times
higher if his genetically identical twin did.
About 1
percent of the population got melanoma, the deadliest form of skin cancer. But
if a person’s fraternal twin got it, his or her risk was 6 percent and if an
identical twin had it, the risk for the other twin was 20 percent.
Some of
the risks for both prostate and breast cancer may be due to effects of sharing
the same womb, the researchers noted. Both are strongly influenced by hormones,
including those affecting a growing fetus.
“Lung
cancer had one of the highest shared environmental components, likely due to
shared smoking habits of pairs of twins,” the researchers wrote.
Cancer
is the No. 1 cause of death in the Nordic countries that took part in the
study. It’s the No. 2 cause of death in the U.S. and many other developed
countries, after heart disease.
https://www.nbcnews.com/health/cancer/just-how-much-cancer-due-genes-about-third-study-finds-n490731
No comments:
Post a Comment