Arya M. Sharma, MD

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.

The strong link between obesity and many forms of cancer is well documented. Not surprisingly, previous studies on obesity surgery have shown dramatic reductions (up to 60%) in overall cancer mortality.

These data are supported by yet another study, this time from Nicolas Christou and colleagues from McGill University in Montreal. Apart from being a renowned Canadian bariatric surgeon, Christou is also the Past-President of the Canadian Association of Bariatric Physicians and Surgeons.

In this study, published in in the latest issue of Surgery for Obesity and Related Diseases, Christou and colleagues conducted an observational 2-cohort study consisting of a treatment cohort of 1035 patients who had undergone bariatric surgery from 1986 to 2002 and a control group consisting of 5746 age- and gender-matched morbidly obese patients identified from an administrative database. The cohorts were followed up for a maximum of 5 years.

While the patients who underwent bariatric surgery (mostly gastric bypass) experienced a weight loss of around 31%, their rate of any cancer diagnosis was only 23% of that in the control group (77% risk reduction!).

The biggest risk reductions were seen for breast (83%) and colorectal (68%) cancers.

Thus, while bariatric surgery has long been documented to remarkably improve a host of obesity-related disorders including type 2 diabetes, dyslipidemia, heart disease, sleep apnea, osteoarthritis and pain, the reduction in cancer morbidity and mortality has perhaps been less well recognized.

I wonder just how much the “Run for the Cure” has contributed to research on obesity and bariatric surgery to date?

AMS
Edmonton, Alberta