#Grand Rounds

Is Obesity Associated with Higher Risk of Early-Onset Colorectal Cancer in Women?

BACKGROUND AND PURPOSE:

While colorectal cancer (CRC) is trending down in those over 50, incidence and mortality have been increasing in those who are 20 to 49 years of age
Liu et al. (JAMA Oncology, 2018) assessed whether obesity and weight gain was associated with higher risk for early-onset colorectal cancer (CRC)

Prospective, ongoing cohort study (Nurses’ Health Study II)
- US female healthy nurses
- No cancer and inflammatory bowel disease
- Ages 25 to 42 at study enrollment
- Follow-up from 1989 to 2011
Data collected including
- Current body mass index (BMI)
- BMI at 18 years of age
- Weight gain since 18 years of age
Definitions
- Overweight: BMI, 25.0-29.9
- Obese: BMI, ≥30.0
Primary outcome: Association between current BMI and risk of early-onset CRC
- Contribution BMI at 18 years of age, weight gain since 18 years of age, and early-life body shape were also analyzed

85,256 women | 1,196,452 person-years of follow-up
- 114 cases of early-onset CRC were documented
- Median age at diagnosis: 45 years
Compared with women with a BMI of 18.5 to 22.9
- Overweight: Relative risk (RR) 1.37 (95% CI, 0.81-2.30)
- Obese: 1.93 (95% CI, 1.15-3.25)
- RR for each 5-unit increment in BMI was 1.20 (95% CI, 1.05-1.38; P = .01 for trend)
- Family history of CRC and without lower endoscopy within the past 10 years did not shift trends
Compared with women with a BMI of 18.5 to 20.9 at 18 years of age
- BMI of 21.0 to 22.9: RR 1.32 (95% CI, 0.80-2.16)
- BMI >23: 1.63 (95% CI, 1.01-2.61; P=.66 for trend)
Compared with women who had gained <5.0 kg or had lost weight
- 20.0 to 39.9 kg gain: RR 1.65 (95% CI, 0.96-2.81)
- ≥40.0 kg gain: RR 2.15 (95% CI, 1.01-4.55; P = .007 for trend)

In this study, higher current BMI and weight gain since early adulthood was associated with higher risk for colorectal cancer in women
The underlying biologic mechanism remains unclear

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