Number of Cancers Linked with Excess Weight Rises from 5 to 13

The International Agency for Research on Cancer (IARC), a division of the World Health Organization, released a new report on the link between weight control and cancer risk. IARC reaffirmed its 2002 conclusion that absence of excess weight – specifically, “body fatness” – lowers risk of cancers of the colon, esophagus, kidney, breast (in postmenopausal women), and uterus.

The 2016 report, published in the New England Journal of Medicine, also adds these 8 cancers to the list:

  • Stomach
  • Liver
  • Gall bladder
  • Pancreas
  • Ovarian
  • Thyroid
  • Multiple myeloma (a blood cancer)
  • Meningioma (a type of central nervous system tumor)

In April this year, IARC convened a working group to reassess the preventive role of weight control in cancer. An expert panel reviewed, overall, some 1,000 studies. They established that the term “body fatness” would be used in lieu of overweight and obesity, and used body mass index as their measure for it.

In addition to finding sufficient evidence to state that a lack of excess weight lowers the risk of 13 types of cancer, the expert panel also noted there is a body of preliminary evidence that intentional weight loss may also have a role in cancer prevention.

The American Cancer Society played a key role in this IARC review. The Society helped fund the working group, which included several peer-reviewed studies authored by Society epidemiologists. In addition, the Society’s Vice President of Epidemiology Research, Susan Gapstur, PhD, MPH, served on the expert panel that reviewed the epidemiologic evidence on the relationship between excess body weight and cancer risk.

We sat down with Gapstur to learn more about the IARC report, and to get additional insight about the role of weight in cancer risk.

Q: Why has the number of cancer sites linked to excess weight increased?

A: When the previous expert panel was convened for the 2002 report, there were smaller and far fewer studies, especially for some less commonly diagnosed cancers. Now we have a much larger body of evidence, primarily from much larger studies, including those where data are pooled from many individual studies. These studies, including our own Cancer Prevention Study II, allow us to better understand the associations of excess body weight with risk of less commonly diagnosed cancers.

Q: The findings of this review aren’t as simple as: Get to a healthy weight and reduce your risk of cancer. Can you explain the nuance of IARC’s message?

A: Based on the available body of evidence, we found that a lack of excess body weight does not increase cancer risk. It’s tricky language. Another way you can think about the findings: There are an additional 8 cancers for which excess weight contributes to cancer risk.

Q: What are some of the factors driving excess body fatness?

A: The IARC working group reaffirmed that eating a diet too high in calories and not moving enough are important contributors to excess body fat, but they noted that the most important factor is an excess amount of calories.

Q: Why does excess weight contribute to cancer risk?

A: There are probably many ways it contributes, and these might be different for different types of cancer. For example, especially in postmenopausal women, fat cells are an important contributor to sex hormones, such as estrogen, that play a role in the development of endometrial and breast cancers, as well as some other cancers. But there are also other mechanisms that are thought to be important for different types of cancer. These include mechanisms related to abnormal glucose metabolism and excess insulin, altered immune responses, and obesity-related inflammation.

Q: In addition to the IARC review, how else has the American Cancer Society contributed to the research on excess weight and cancer?

A: The American Cancer Society’s epidemiologists have been studying the role of obesity in premature mortality for many decades. In fact, the first large epidemiologic study showing that overweight/obesity contributed to premature death due to all causes, cardiovascular disease and cancer was first published by Society investigators in 1979, using Cancer Prevention Study I data. A particularly important paper in the New England Journal of Medicine in 2003 showed that obesity contributes to death from at least 10 different cancer sites; that paper used data from Cancer Prevention Study II. Since then, we’ve published and contributed to numerous large studies that have looked in detail at the associations of overweight/obesity with risk of many different types of cancer.

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