Big Drop in Malignant Melanoma Rate After Bariatric Surgery

VIENNA — Obese patients who undergo weight loss surgery appear to experience a substantial reduction in the risk of both skin cancer in general and malignant melanoma in particular, new results from a landmark prospective study indicate.

Presenting 18-year follow-up data in more than 4000 obese patients, the researchers showed that bariatric surgery was associated with a 42% reduced risk of skin cancer compared with usual care.

Moreover, Magdalena Taube, Department of Molecular and Clinical Medicine, Institute of Medicine, University of Gothenburg, Sweden, and colleagues found that the risk of malignant melanoma was cut even further, by 61%, in adjusted analyses.

The research was presented May 24 here at the European Congress on Obesity (ECO) 2018.

"In this long-term study, bariatric surgery reduced the risk of malignant melanoma," the authors say in a press release. "This finding supports the idea that obesity is a melanoma risk factor and indicates that weight loss in individuals with obesity can reduce the risk of a deadly form of cancer that has increased steadily in many countries over several decades," they add.

During a press conference, Taube explained that there has been a steady increase in the incidence of malignant melanoma.

Indeed, a recent report by the charity Cancer Research UK showed that cases of malignant melanoma have more than doubled in the United Kingdom since the 1990s. It is now the fifth most common cancer in men and women, with more than 15,000 cases and 2000 deaths annually.

While the relationship between obesity and a number of mainly solid cancers is well established, and some studies have described an association between obesity and melanoma, Taube said that, so far, the evidence hasn't been that robust for an association between obesity and skin cancers.

She pointed out, however, that intervention studies can lend support to a potential association by showing, for example, whether the putative effect of obesity on melanoma risk can be reversed.

Furthermore, "as bariatric surgery is the most efficient way to accomplish long-term weight loss in obese patients, we asked the question: Can weight loss surgery reduce melanoma risk in patients with obesity?"

Data From Landmark SOS Study Suggests Obesity a Factor in Melanoma

Researchers examined data from the Swedish Obese Subjects study, an ongoing prospective, controlled intervention trial comparing bariatric surgery with usual nonsurgical care.

Between 1987–2001, 6095 individuals aged 37–60 years with a body mass index (BMI) of > 34 kg/m² in men and > 38 kg/m² in women were screened for inclusion, resulting in 2010 patients being assigned to bariatric surgery and 2037 to usual care.

The two groups were matched on 18 variables, including age, sex, anthropometric measurements, cardiovascular risk factors, psychosocial variances, and personality traits.

Participants completed a clinical examination, several questionnaires (including on alcohol intake and smoking), and blood chemistry analyses. Their records were also linked to the Swedish National Cancer Registry, Swedish Cause of Death Registry, and Swedish Population Registry.

After a median follow-up of 18.1 years, the team found that, although body weight remained relatively constant in the usual care group, it decreased by 25% after 1 year in the bariatric surgery group before stabilizing at between 15% and 20% below baseline.

During follow-up, there were 23 cases of skin cancer in the bariatric surgery group versus 41 in the usual care group, yielding an adjusted hazard ratio of 0.58 (P = .044).

And when researchers looked specifically at the incidence of malignant melanoma, the reduction was even greater, at 12 cases in the bariatric surgery group versus 29 in the usual care group, for an adjusted hazard ratio of 0.39 (P = .008).

"To understand if there were any possible predictors that could explain the treatment benefit, we performed an interaction analysis on different parameters that could be important, like smoking, diabetes, fasting glucose, insulin, and so on, but we could see no interactions," Taube said.

She concluded that the data "give additional support for a link between obesity and skin cancer, and for the idea that weight loss reduces [skin] cancer incidence."

"It also suggests that obesity should be considered a preventable risk factor for malignant melanoma."

A Big Effect on Melanomas, but Underlying Mechanism Still Unclear

Approached for comment, Jason Halford, PhD, Chair in Biological Psychology and Health Behaviour, University of Liverpool, UK, said because obesity "is an inflammatory disease and inflammation is an important component of cancer...I wonder if there's a link there?"

However, speaking to Medscape Medical News, he pointed out there could be another, simpler explanation.

He said that, unless a bariatric surgery patient has undergone corrective procedures to deal with their extra "hanging" skin and engages in physical activity to tone their body, they may not be happy with their self-image and cover up their bodies more, resulting in less sun exposure.

However, Taube said she does not believe sun exposure is driving the difference in incidence in skin cancers seen in their study.

Previous evidence from mouse and human studies suggests that, although sun exposure is one process the drives melanoma risk, obesity may be another separate mechanism, "and that might explain why different melanomas behave differently."

She told Medscape Medical News that bariatric surgery itself may also play a role in altering malignant melanoma risk. "Perhaps it's something to do with hormones, metabolic factors, or inflammation," she said, noting that "systemic inflammation goes down after bariatric surgery, and we know that leptin hormone release from fat tissue also drops after surgery."

Previous studies have suggested that melanoma risk is positively associated with serum leptin levels and the hormone acts as a growth factor for the disease.

Taube said further research is needed to identify the underlying mechanisms, but based on the current data, "we can say this is happening, and it's quite a big effect."

Coauthors Martin Bergo, PhD, has received speaker fees from Baxter Medical and LEO Pharma, and Lena Carlsson, MD, PhD. has received lecture fees from AstraZeneca, Johnson & Johnson, and Merck Sharpe & Dohme.

European Congress on Obesity 2018. May 24, 2018; Vienna, Austria. Abstract O7.6.

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