Reducing the risk of cancer with bariatric surgery: The need for evidence to guide practice

The incidence of cancer has increased worldwide with a projected rising trend in the future. ¹ Obesity is believed to be one of the major contributing factors. ¹ The International Agency for Research on Cancer (IARC) has noted a significant association between obesity and 13 cancer types, known as obesity-related cancers. ² The causative mechanisms, thus, remain partly elusive. From a cancer-preventive perspective, a natural question would be whether sustainable weight loss may reduce an individual’s lifetime risk of cancer.

Strategies for weight loss range from diet and exercise to obesity management medications (OMMs) and metabolic bariatric surgery (MBS). The benefit of MBS in achieving sustained weight loss and reducing risk of metabolic syndrome has consistently been demonstrated to exceed other forms of therapy. ³ Recent studies indicate that MBS can significantly reduce cancer risk for some cancers. ⁴ Several recent observational cohort studies have explored the association between weight loss and cancer risk after MBS, focusing on total cancer risk and obesity-related cancers.^{5 –7} Collectively, these studies paint a fairly uniform picture: MBS is associated with a significant reduction in overall cancer risk, especially for obesity-related cancers. Although the exact mechanism for the reduction in the risk of cancer development after MBS remains unclear, it is conceivable that the shift can be attributed to the myriad of molecular, metabolic, and endocrine changes that accompany weight loss after MBS. An increasing number of studies have assessed cancer-related mortality post-bariatric surgery.^4,5,7 A recurrent finding is a significant reduction in cancer-related death rates even up to 55% in patients after MBS as compared to the non-operated control group. ⁴

The literature consistently points to a probable link between the magnitude of weight loss post-bariatric surgery and total cancer risk reduction (evident dose-response effect) at the population level, supporting the causality argument. ⁵ The evidence of surgical weight loss and cancer risk is heterogenous with largely inadequate follow-up, when compared to other major contributors to cancer risk, for example, cessation of smoking, where it can take up to 20 years for detecting the effect. ⁸ The perceived benefits of MBS may thus be influenced by other factors. The cost-effectiveness of MBS in reducing obesity-related health complications is undisputed. However, globally, MBS is associated with a sizable out-of-pocket expense. ⁹ Thus, it would stand to reason that there may be an additional component of the overall commitment toward a more healthy lifestyle of an individual seeking MBS, acknowledging the importance of weight reduction on their overall health. These individuals are also likely to be financially situated in a higher socio-economic group. The relationship between socio-economic deprivation and cancer risk, access to care, and cancer outcomes is well documented. ¹⁰ The contribution of socio-economic bias has never been tested within studies comparing outcomes of MBS and cancer risk reduction. Another important and only partially explored ⁵ aspect is the relationship between the extent and sustainability of individual weight loss and cancer risk reduction.

The findings of cancer risk related to weight loss after MBS may also hold promise for less-invasive treatments of obesity. OMMs, such as glucagon-like peptide-1 (GLP-1) analogues have demonstrated consistent and clinically relevant weight reduction with also improving glycemic profiles and reducing cardiovascular risks. ¹¹ If future research would consolidate a link between OMMs and decreased cancer incidence, this could contribute to a ground-breaking shift in cancer prevention. However, it is crucial to consider weight loss sustainability, potential side effects, cost implications, and accessibility to OMMs when evaluating these medications.

Weight loss after surgical, pharmacological, or a combination therapy may emerge as a main strategic pillar to reduce cancer risk and mortality. We need to better understand the involved underlying mechanisms involved to empower healthcare systems moving forward in prioritizing the best weight loss strategies as a means to reduce cancer risk.