Obesity is already linked to a higher risk of colon or
rectal cancer, but a new study suggests this risk is even greater for obese
people who have undergone weight-loss surgery.
Based on a study of more than 77 000 obese patients, Swedish
and English researchers found the risk for colorectal cancer among those who
have had obesity surgery is double that of the general population.
Though colorectal cancer risk among obese patients who
didn't have the surgery was just 26% higher than in the general population,
researchers said the results should not discourage people from going under the
should not be used to guide decisions made by patients or doctors at all until
the results are confirmed by other studies," said Dr Jesper Lagergren, the
new study's senior author and a professor at both the Karolinska Institute in
Stockholm and King's College London.
Having surgery to
Each year more than 100 000 people in the US have surgery to
treat obesity. Lagergren and his colleagues point out in their report,
published in the Annals of Surgery, that obesity is tied to elevated risks for
a number of cancers, including colorectal, breast and prostate. Whether surgery
to lose weight can affect those risks is uncertain.
Two earlier studies, one from the US and the other from
Sweden, found that the chances of obesity-related cancers decline after women
have weight-loss surgery. But an earlier study from Lagergren's group found the
risks for breast and prostate cancers were unaffected by obesity surgery, and
colorectal cancer risk increased.
To investigate that finding further, Lagergren's team
collected 29 years' worth of medical records on more than 77 000 people in
Sweden who were diagnosed as obese between 1980 and 2009. About 15 000 of them
underwent weight loss surgery.
People in study who
In the surgery group, 70 people developed colorectal cancer
- a rate that was 60% greater than what would be expected for the larger
Swedish population. When the researchers looked only at people who had surgery
more than 10 years before the end of the study period, the number of cancer
cases was 200% greater than the expected risk for the general population.
In contrast, 373 people in the no-surgery group developed
colorectal cancer, which was 26% more than would be expected in the population
and that number remained stable over time. A two-fold increased risk for
colorectal cancer is not a "negligible risk increase, but it should not be
of any major concern for the individual patient since the absolute risk is still
low," Lagergren told Reuters Health in an email.
In the US, for instance, 40 out of every 100 000 women and
roughly 53 out of every 100 000 men develop colorectal cancer each year.
Doubling that risk would make the annual figures 80 out of every 100 000 women
and 106 out of every 100 000 men. Lagergren said that more studies are needed
to confirm his results before they should be included in clinical
decision-making about whether patients should undergo weight-loss surgery.
The study results cannot prove that the surgery is the cause
of the elevated cancer risk. And, Lagergren says it's also not clear why the
surgery might be tied to an elevated risk of colorectal cancer. One possibility
is that dietary changes after surgery, and increasing protein in particular,
could raise cancer risk, he speculated.
Because the gut plays a significant role in the immune
system, he added, "Another potential factor is that the bacteria that
naturally reside in the intestines may change after surgery and alter future
cancer risk."Lagergren noted that he also couldn't rule out the
possibility that residual excess weight and weight gain after surgery might be