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Obesity May Dim Colon Cancer Survival

Study Shows Worse Survival Rates for the Very Obese and Underweight
WebMD Health News
Reviewed by Louise Chang, MD

Nov. 15, 2006 -- Colon cancer survival may be less likely for patients who are very obese or too thin at diagnosis.

The University of Chicago's James Dignam, PhD, and colleagues report that news in the Journal of the National Cancer Institute.

They aren't blaming colon cancer on weight or promising survival for patients who are in shape.

Doctors often can't explain exactly why someone develops, survives, or dies from cancer. Many factors are likely involved.

More studies are needed to see if reaching a healthy weight boosts colon cancer survival.

"One first step would be to investigate whether modifying diet and exercise habits for patients after treatment would have a positive impact on colon cancer outcomes," Dignam says in a University of Chicago Medical Center news release.

Colon Cancer Study

Other studies have linked obesity to worse odds of getting colon cancer.

Dignam's team focused on people who already had colon cancer. The goal: See if BMI (body mass index) affects colon cancer survival.

BMI measures weight in relation to height and is used to gauge obesity.

The researchers studied 4,288 people diagnosed with stage ll or stage lll colon cancer between 1989 and 2004.

The patients got surgery and chemotherapy. On the first day of chemotherapy, their height and weight were measured.

The researchers calculated the patients' BMI, which ranged from about 14 to 52, with an average BMI of 26.1, which is in the overweight category.

Here are the details on the patients' BMI:

  • 3% were underweight (BMI less than 18.5)
  • 42% had normal weight (BMI of 18.5 to 24.9)
  • 36% were overweight but not obese (BMI of 25 to 29.9)
  • 13% were obese (BMI of 30 to 34.9)
  • 6% were very obese (BMI greater than 35)

Tracking Colon Cancer Survival

The patients were followed for 11 years, on average.

During that time, those who were very obese were 28% more likely to die of colon cancer and 38% more likely to have colon cancer return, compared with those of normal weight.

Underweight patients were also at risk. They were 49% more likely to die during the follow-up period, compared with patients of normal weight.

But the underweight patients weren't more likely to have colon cancer return. Their higher death rate wasn't due to colon cancer and may have been tied to other conditions.

Relationship Unclear

It's not clear how weight affects colon cancer survival, write the researchers.

They note some limits to the data. For instance, patients' BMI was only checked once; any weight changes weren't recorded.

"Given the increasing proportion of Americans with a BMI greater than 35 and the fact that these individuals are overrepresented among colon cancer patients, we need to find out why extra weight has such a harmful impact and come up with new ways to counter that," says Dignam.

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