Importance: Pancreatic cancer rates in the United States have steadily increased since the early 2000’s despite declines in smoking. This increase is not easily explained by population increases in body mass index (BMI) given the relatively weak association between BMI and pancreatic cancer risk typically observed in epidemiologic studies. Most of these studies, however, assessed BMI in older adulthood, which may be less strongly associated with pancreatic cancer than BMI earlier in adult life.

Objective: To examine the association between BMI and pancreatic cancer mortality by age at BMI assessment.

Design: Prospective cohort study.

Setting: Cancer Prevention Study II (CPS-II), a nationwide study of cancer mortality enrolled in 1982 and followed through 2014.

Participants: 963,317 US adults aged 30 to 89 years at enrollment.

Exposure: BMI calculated from height and weight reported at enrollment.

Main outcomes and measures: A total of 8,354 participants died of pancreatic cancer during follow-up. Hazard ratios (HRs) for BMI were calculated using multivariable proportional hazards regression models. Population attributable fractions by birth cohort were calculated using HRs from CPS-II and BMI distributions from nationally representative National Health and Examination Surveys (NHANES).

Results: HRs declined with increasing age at BMI assessment. HRs per 5 BMI units among those aged 30-49, 50-59, 60-69, and 70-89 years at assessment were 1.25 (95% confidence interval (CI) 1.18-1.33), 1.19 (95% CI 1.14-1.23), 1.14 (95% CI 1.08-1.21) and 1.13 (95% CI 1.02-1.26), respectively (p-trend = 0.005). The prevalence of obesity in early middle age is substantially higher in more recent US birth cohorts than in earlier ones. Therefore, based on a HR of 1.25 per 5 BMI units at age 45 years, we estimate that 28% of pancreatic cancer deaths in the US among those born from 1970-74 will be attributable to BMI levels > 25 kg/m2, nearly twice the equivalent percentage in those born in the 1930s.

Conclusions and Relevance: BMI before age 50 may be more strongly associated with pancreatic cancer risk than BMI at older ages. These results underscore the importance of preventing excess weight gain before middle age for reducing rates of this highly fatal cancer.

Citation Format: Eric J. Jacobs, Christina C. Newton, Alpa V. Patel, Victoria L. Stevens, Farhad Islami, W. Dana Flanders, Susan M. Gapstur. The association between body mass index (BMI) and risk of pancreatic cancer depends on age at BMI assessment [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 3281.