While I am taking a brief break from clinics and other obligations (including daily blog posts), I will be reposting past articles, which I still believe to be relevant but may have escaped the attention of the 100s of new readers who have signed up in the past months.

The following was first posted on 04/22/08

Yesterday’s big news was the study by Kerry Courneya, professor and Canada Research Chair in Physical Activity and Cancer at the University of Alberta, published in CANCER.

I am not going to repeat the findings or the data here because this was nicely summarized by Sharon Kirkey from Canwest News Service in the Edmonton Journal.

The bottom line is that cancer survivors are apparently not exercising more or eating healthier than everyone else, and are therefore at least as, if not even more, likely to develop obesity than the average Canadian.

This is particularly true for survivors of breast and colon cancer, which are particularly likely to recur with lack of physical activity, unhealthy eating and weight gain.

The dramatic impact of weight on cancer risk is perhaps best demonstrated by the observation that obesity surgery, which on average reduces body weight by 25%, results in an almost 60% reduction in cancer mortality! (see Adams et al. for an example of such a study).

I guess it just goes to show that cancer survivors are no less susceptible to the consequences of our obesogenic environment, which certainly does not make weight control easy, even at the best of times.

That is of course, unless there is something special about surviving cancer that makes you more likely to gain weight - an interesting hypothesis pursued by other researchers here at the University of Alberta.

I can think of a number of reasons why surviving cancer could predispose to weight gain: “catch-up” fat, depression, “post-traumatic” stress, anxiety, susbtance abuse, “overfeeding”, immobility, medications, and perhaps a few others.

Whatever the reasons, it looks like we may now need intervention programs to specifically address weight gain and obesity in cancer survivors?

For one, educating cancer survivors about the links between excess weight and cancer would be a start.

My sense is that most people still don’t fully appreciate the close link between obesity and cancer - all the more reason to promote healthy eating and active living for all.

Obesity prevention (and treatment?) may well turn out to be the most effective cancer prevention strategy (short of smoking cessation) - looks like a whole new field for bariatric health professionals?

I guess we’d call them Bariatric Oncologists?

AMS
Edmonton, Alberta

Lars Sjöström

Regular leaders are already well aware of the increasing evidence that losing weight may be the most effective cancer prevention strategy, short of smoking cessation.

Following close on the heels of a previous study on this topic, the latest issue of Lancet Oncology publishes another major study demonstrating the substantial effect of (surgical) weight loss on the incidence of cancers.

In this study, Lars Sjöström and colleagues from the University of Gothenburg, Sweden, report on the incidence of cancers in the Swedish Obese Subjects Study: a prospective, controlled intervention trial of bariatric surgery.

The SOS study started in 1987 and involved 2010 obese patients who underwent bariatric surgery and 2037 matched obese controls, who received conventional treatment.

Over the 11-year course of the study, cancer follow-up rate was 99.9%. Patients who underwent bariatric surgery had a sustained mean weight reduction of 19.9 kg, whereas the mean weight change in controls was a gain of 1.3 kg.

The number of first-time cancers after inclusion was lower in the surgery group (n=117) than in the control group (n=169), a risk reduction of 33%. There were, however, important sex differences in this effect.

While in women, the risk of first-time cancers was reduced by 42% (79 vs. 130), there was no difference in cancer incidence with weight loss in men (39 vs. 38).

The results were similar even when cancer cases in the first 3 years of observation were excluded.

Thus, this study once again confirms the substantial effect of (surgical) weight loss on the incidence of cancers (at least in women).

These finding perhaps give a whole new meaning to “Running for the Cure”.

AMS
Duchesnay, Quebec

For anyone still skeptical about the tremendous benefit of bariatric surgery for severe obesity in reducing cancer mortality, here is a new study by Ted Adams and colleagues from the University of Utah, published in the latest issue of OBESITY.

Adams and colleagues examined cancer incidence and mortality data through 2007 from the Utah Cancer Registry (UCR) in 6,596 Utah patients who had gastric bypass for severe obesity (1984-2002) and 9,442 severely obese persons who had applied for Utah Driver’s Licenses (1984-2002).

Over a 24-year follow-up period (mean 12.5 years), total cancer incidence was almost 25% lower in the surgical group compared to controls, this difference being largely attributable to a decreased incidence of cancers at advanced stages in the surgical group.

Overall cancer mortality was 46% lower in the surgery group compared to controls. Interestingly, while the reduction in new cancers was largely limited to cancers known to be related to obesity (e.g. breast, colon, etc.), the reduction in mortality was from all cancers.

This analysis is consistent with previous reports on up to 60% reduction in cancer mortality in bariatric surgical patients.

It appears that short of smoking cessation, bariatric surgery is perhaps the most effective measure for prevention of cancer and lowering cancer mortality in modern medicine.

AMS
Toronto, Ontario
(from the meeting on Building Authentic Trust to Address the Epidemic of Obesity and Chronic Diseases)

I have previously blogged on the fact that women with a BMI of 35 or higher are nearly 40 percent less likely than normal weight women to have had a Pap test (for detection of cervical cancer) in the last 12 months (see Pap Gap - June 12-2008).

It seems that there are also significant deficits in screening for breast cancer in obese women (J Gen Intern Med. 2009 May).

In this systematic review of the literature on obesity and mammography in the United States, Nisa Maruthur and colleagues (including my friend Fred Brancati) from Johns Hopkins University, Baltimore, MD, USA, included 17 studies that met their selection criteria.

Increasing BMI was associated with a significantly reduced likelihood of having received a mammography in the last 2 years (post-menopausal women with BMI>35 were almost 20% less likely to have received this exam), compared to normal-weight women.

It appears that as for Pap exams for cervical cancer, obese women are also less likely to be screened for breast cancer. While the reasons for this finding are not clear, it may well be that these lower screening rates partly explain the higher breast cancer mortality seen in severely obese women.

Given that the substantially increased risk of breast cancer in post-menopausal obese women, it will be important to fully understand the determinants and barriers to cancer screening in this vulnerable population.

AMS
Edmonton, Alberta

A new report released yesterday by the World Cancer Research Fund and the American Institute for Cancer Research states that most cancers are preventable.

Poor diet, lack of exercise, obesity and smoking account for the vast majority of cancers; the role of genetic factors is by far overrated.

Indeed, the dramatic impact of obesity on cancer is now increasingly appreciated – one in three cancers may be caused by obesity (or as a result of lifestyle factors that promote obesity). It is therefore perhaps not surprising, that large prospective studies have shown an almost 60% reduction in deaths from cancer with bariatric surgery.

But how does obesity (or poor diet) promote cancers?

New insight into the mechanistic relationship between high fat intake (not uncommon in obese individuals) and cancer come from a recent study published in BMC Cancer by Thuc T Le and colleagues from, Purdue University, West Lafayette, Indiana, USA.

Their study showed that feeding cancer-prone mice a high fat diet leads to increased fat accumulation in cancer cells, which in turn is incorporated onto the cancer cell membranes, thereby reducing cell-cell contact, increasing surface adhesion, and promoting tissue invasion by cancer cells.

They also showed that visceral adiposity and increased plasma free-fatty-acid levels (a common finding in abdominally obese individuals) are associated with early rise in circulating tumour cells and increased lung metastasis.

Thus, these studies provide insight into a mechanism directly linking increased fat intake, abdominal adiposity, and higher circulating fatty acid levels to the spread of cancer cells.

Evidently, much of cancer should perhaps now be best classified as a “lifestyle disease” (a term often used to “trivialize” obesity).

Prevention and treatment of obesity may prove to be the most effective “cure” for cancer after all.

AMS
Edmonton, Alberta
Hat tip to Jacob Berkowitz for bringing the latter study to my attention.