The Risk of a Second Cancer After the First – The Impact of Overweight and Obesity

Survivorship after cancer treatment is highly important for improving quality of life and preventing recurrence or second primary cancers . However, body weight may be an important risk factor during this period. On September 17, 2024, JAMA Network Open published a study by Bodelon and colleagues showing that overweight or obese cancer patients have a higher risk of second primary cancers, particularly obesity-related cancers. These findings emphasize the need to monitor and manage body weight after cancer treatment.

Study Details

The study examined data from the Cancer Prevention Study II Nutrition cohort, covering 21 US states. It included patients diagnosed with their first nonmetastatic cancer between 1992 and 2015. Body mass index (BMI) at the time of the first diagnosis was recorded. Cancer diagnoses were confirmed through surveys every two years and comparisons with medical records and state cancer registries.

Key Findings

The study included 26,894 patients diagnosed with a nonmetastatic primary cancer. The mean age at first diagnosis was 72.2 ± 6.5 years. At diagnosis, 11,497 participants (42.8%) were classified as overweight and 4,684 (17.2%) as obese.

BMI (body mass index) is calculated by dividing weight (kg) by the square of height in meters: BMI = weight (kg) / [height (m)]². It is used to assess whether someone is underweight, of normal weight, overweight or obese.

In the study, overweight was defined as a BMI between 25 and 29.9 kg/m², while obesity was defined as a BMI of 30 kg/m² or above.

Median follow-up was 7.9 years (interquartile range = 3.4–13.6 years). During this period, 3,749 patients (13.9%) were diagnosed with a second primary cancer, of whom 1,243 (33.2%) had an obesity-related second primary cancer.

BMI and the Risk of a Second Primary Cancer

Compared with patients with a normal BMI (18.5-24.9 kg/m²), those who were overweight (25-29.9 kg/m²) had a risk of developing a second primary cancer that was 15% higher (adjusted hazard ratio [HR] = 1.15, 95% confidence interval [CI] = 1.07–1.25).

The risk was even more pronounced among those who were obese (≥ 30 kg/m²): a 34% increase (HR = 1.34, 95% CI = 1.21–1.48).

Specifically for obesity-related second cancers , the risk increased by 40% in overweight individuals (HR = 1.40, 95% CI = 1.22–1.61), while the increase reached 78% in obese individuals (HR = 1.78, 95% CI = 1.51–2.11).

Study Conclusions and Recommendations

The researchers summarized their findings as follows: "This cohort study found that older cancer survivors who were overweight or obese at their first diagnosis had a higher risk of developing a second cancer, particularly an obesity-related cancer. Given the prevalence of overweight and obesity among cancer survivors, it is important to implement survivorship guidelines promoting weight management and raise awareness of second cancers among physicians and survivors."

Conclusion and Next Steps

This study clearly demonstrates the impact of excess body weight after cancer treatment on the development of second primary cancers. Weight management among survivors can improve quality of life and has the potential to reduce second cancer risk. Incorporating weight management strategies into survivorship care is important for improving long-term outcomes. Patients and healthcare professionals should therefore be informed, and appropriate treatment plans developed.