A new study led by researchers at the American Cancer Society (ACS) shows that older adult cancer survivors with excess body weight at the time of their first cancer diagnosis are at higher risk of developing a second cancer, especially an obesity-related cancer like breast or colorectal cancer. These findings have important public health implications given the high prevalence of cancer survivors with excess body weight. The findings will be presented at this year’s annual meeting of the American Society of Clinical Oncology (ASCO) in Chicago, May 31-June 4, 2024.

Researchers, led by Dr. Clara Bodelon, senior principal scientist, survivorship research at the American Cancer Society, analyzed data among men and women enrolled in the Cancer Prevention Study II Nutrition cohort who were diagnosed with a first non-metastatic incident cancer between 1992 and 2015. Survivors were followed-up until 2017 for the diagnosis of a subsequent primary malignancy. Outcomes of interest were any second cancers and obesity-related second cancer as defined by the International Agency for Research on Cancer (IARC). Excess body weight was define using self-report body mass index (BMI). BMI was assessed prior to and after the first primary cancer diagnosis, but no major changes in BMI were observed during the follow-up period.

Key Findings

• The results included 26,894 participants diagnosed with a first cancer.
• The median age at diagnosis of the first cancer was 72.2 years. Most participants were men (59%), overweight or obese (60%) and diagnosed with localized disease (71%).
• During a median of follow-up of 7.5 years, 3,749 participants were diagnosed with a second cancer, including 1,243 being diagnosed with obesity-related second cancers. Approximately 90% of second malignancies were diagnosed at least 1 year, and 70% at least 5 years after the first cancer.
• Compared with cancer survivors whose BMI was in the normal range, those who were overweight or obese were at 15% and 34% increased risk of any second cancer and 40% and 78% increased of obesity-related cancers.
• In particular, obesity was associated with 39% increased risk of breast second cancers and a two-fold increased risk of colorectal second cancers.

Researchers stress weight loss strategies should be considered and heightened awareness of second cancers among physicians caring for adult cancer survivors.

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