Lifetime overweight and obesity: impact on cancer survival

  • Topic: Combination of cancers
  • Institution: International Agency for Research on Cancer (IARC)
  • Country: France
  • Status: Ongoing

Scientific abstract

(View plain language abstract)

Background

Obesity is an established risk factor for several types of cancer and its prevalence has been rising across the globe, rendering it a key public health concern. As countries progress within the obesity epidemic and life expectancy continues to increase, more individuals experience earlier and longer durations of overweight during their life course, with still largely unknown consequences on the cancer burden. To date, few studies have investigated the relationship between obesity and cancer survival from a life course perspective. Yet this knowledge is vital for the planning and implementation of effective treatment and follow-up strategies.

Hypothesis and objectives

Overweight and obesity have been linked to poorer cancer prognosis. Studies taking into account an individual's lifetime exposure to overweight showed that a longer overweight duration increases cancer risk. In this project, we propose to test the hypothesis that it also leads to poorer survival. Specific objectives include:

  1. To pool data from large international cohort studies with repeated anthropometric assessments before cancer diagnosis to derive lifetime overweight/obesity and with follow-up data since cancer incidence to estimate survival.
  2. To investigate the role of overweight and obesity duration on overall and cancer-specific survival from postmenopausal breast, colon and rectal cancer.
  3. To assess direct and indirect effects of overweight and obesity duration on cancer survival, by looking into the individual and combined contributions of obesity and other risk factors, including physical inactivity, smoking, unhealthy diet and diabetes.

Settings and methods

The overall impact of overweight and obesity duration on cancer survival will be investigated by means of a pooling project, involving data from large cohorts and population-based registries with repeated anthropometric assessments and hospital admission data in Europe, China, Australia and the US. Using data from persons with at least two assessments of height and weight, BMI will be modelled across ages for every study participant using a quadratic growth model with a random intercept and random slope. Overweight duration and intensity for every study participant will then be estimated from the model. Flexible parametric survival models will be fitted to assess the relationship between overweight duration and survival from postmenopausal breast, colon and rectal cancer, adjusting for physical activity, smoking, alcohol use, diabetes, diet, post-hormonal treatment use and reproductive factors, whenever available. Further cancer-specific adjustments will be made for stage at diagnosis, treatment and hormone receptor status (breast cancer only). Finally, mediation analyses will be carried out to quantify the direct and indirect effects of excess BMI and other related risk factors, specifically physical inactivity, unhealthy diet, hormone use, diabetes and smoking, on cancer survival.

Impact

In view of the ongoing and aggravating obesity epidemic worldwide, insights into the relation between cumulative overweight exposure and cancer survival have become vital for the planning and implementation of effective prevention and treatment strategies. This project will contribute new insights into the role of lifetime overweight and obesity in relation to cancer survival and build a platform for future research by means of an international pooling project.

Plain language abstract

Background

Research has shown that high body weight causes certain types of cancer. It also showed that it takes many years from having a high body weight until cancer develops. Because the number of people who are having a high body weight is increasing and many are also gaining weight earlier in life (ie during childhood), the consequences of this development on the chance to survive cancer are still largely unknown. Only very few studies have looked at changes in weight during the life course and considered the years spent with high body weight and how this affects the prognosis for cancer patients. Yet this is important to provide effective and targeted cancer treatment.

Aims and objectives

Studies have shown that being overweight or highly overweight (also called obese) is related to a poorer survival after cancer diagnosis. Information on body weight at different ages throughout life has been reported to better predict the chance of getting a cancer than body weight that is measured at only one point in time. In this project, we look to study whether more years of life spent with overweight before being diagnosed with cancer has an impact on the chance to survive cancer. This will be done by looking at and combing data from several countries. Furthermore, we aim to look into how much of this effect is actually caused by high body weight and how much is actually related to insufficient physical activity, smoking, unhealthy diet or diabetes factors that have also been reported to increase the risk of developing a cancer.

How it will be done

We will use data from a number of large studies from different European countries, China, Australia and the USA to estimate the overall impact of overweight and obesity duration on cancer survival. Repeated assessments of height and weight will be used to estimate how many years each person spent with overweight or obesity over their lifetime. We will then use statistical techniques to see the impact of the number of years spent with overweight and obesity on cancer survival, taking into account the effects of other important factors, such as physical activity, smoking, alcohol use, diet and having been diagnosed with diabetes. We will also include information on how advanced the cancer of each patient was at diagnosis and what kind of treatment the patient received. Finally, we will use new calculation methods to differentiate how much of this effect is actually caused by high body weight and how much of it is related to the other factors mentioned earlier.

Potential impact

Worldwide, more and more people are becoming overweight and obese. Knowing more about the exact relationship between obesity and survival among cancer patients will enable us to improve cancer prevention and make cancer treatment more efficient by contributing to a better cure. Bringing together data from different countries and sources, this project will also represent an important base for future research.