Obesity and Cancer: The Link

The Panel’s Recommendation

Obesity and Cancer: The Evidence

• AICR/WCRF is continually updating the evidence

• Breast cancer update released in 2009

- 2007 expert report based on 873 studies

- Update included additional 81 studies

- Findings strengthened previous conclusions that women can reduce risk by maintaining low body fat, being physically active, drinking no alcohol and breastfeeding their children.

• Updates of colon and prostate cancer are now underway.

Obesity and Cancer: Mechanisms

• Adipose tissue is an active endocrine organ

• Mechanisms by which adipose tissue may influence cancer risk

- Production of sex steroid hormones (e.g., estrogen, androgen)

- Effects on insulin sensitivity and production of insulin-like growth factors

- Actions on other hormones in adipose tissue (e.g., leptin, adiponectin)

- Increases in oxidative stress and chronic low-grade inflammation that affect the body’s immune response

Developing the Preventability Estimates

• Several sources of data were used:– Current estimates of cancer incidence in the US and the actual number of cancer

cancers

– Survey data on the prevalence of rates of different levels of overweight/obesity in the US population

– Estimates of the risk of developing specific cancers associated with these levels of overweight, based on key studies in the literature

• These data are combined to compute a population attributable fraction (PAF), and the estimated numbers of preventable cancers

Obesity and Cancer: Conclusions

• A healthy diet can help sustain a healthy weight and lower risk of cancers

• regular physical activity protects against the buildup of excess body fat and against cancer, independently

Lifestyle Habits and Breast Cancer Survival

• Higher BMI and lower physical activity are associated with a reduced risk of breast and colon cancer specific survival.

• Current cancer therapies do not address the association of obesity and sedentary lifestyle effects on prognosis.

• Obesity and physical inactivity are common before and after a breast cancer diagnosis.

Mortality from Cancer According to BMI for U.S. Women in the Cancer Prevention Study II

Calle, E. et al. N Engl J Med 2003;348:1625-1638

Weight and Survival in Early-Stage Breast Cancer

BMI (kg/m2)

Es

tim

ate

d R

ela

tiv

e R

isk

of

Ad

ver

se E

ven

t

20 30 40 50

05

1015

25 35 45 55

Distant Recurrence, p=0.0005

Death, p=0.0007

Goodwin et al, JCO 2002

Nurses’ Health Study: Physical activity after breast cancer diagnosis

0

0.10.2

0.30.4

0.5

0.60.7

0.80.9

1

Recurrence BRCA Death Total Death

<33-8.99-14.915-23.9

MET-Hrs/week

*p=0.05, # p<0.004

MET-hr/wk

Holmes M et al JAMA 2005

P = .05

HR

P= .004 P = .003

The HEAL Study: Physical Activity after Diagnosis

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

BC Death Total Death

0

>0 - 9

9+

Haz

ard

Rat

io f

or

Dea

th MET-hr/wk

Irwin ML et al JCO, 2008.

P = .04P = .46

Benefits of Increasing Post-Diagnosis PA

• Need to encourage cancer survivors to maintain (if Need to encourage cancer survivors to maintain (if active prior to diagnosis) or increase physical activity active prior to diagnosis) or increase physical activity after diagnosis.after diagnosis.

• Physical activity is associated with numerous benefitsPhysical activity is associated with numerous benefits– Decreasing adverse side effects of surgery and treatmentDecreasing adverse side effects of surgery and treatment

– Improving quality of life and fatigueImproving quality of life and fatigue

– Improving fitness, functional capacity, and Improving fitness, functional capacity, and body composition body composition

– Decreasing serum hormones and growthDecreasing serum hormones and growth

factorsfactors

– Improving cancer-specific survival and Improving cancer-specific survival and all cause survival all cause survival

9490

87

52 51

46 46

38

0

10

20

30

40

50

60

70

80

90

100

% o

f Am

eric

ans

wh

o B

elie

ve it

to

be

a C

ause

of

Can

cer

2009 Cancer Risk Awareness

2009 Cancer Risk Awareness

35

45 4446

51

0

10

20

30

40

50

60

70

80

90

100

2001 2003 2005 2007 2009

OBESITYOBESITY

Percentage of Americans who

Believe it to be a Cause of Cancer

Percentage of Americans who

Believe it to be a Cause of Cancer

YearYear

0%

5%

10%

15%

20%

25%

30%

35%

40%

Cancer Heart Attack Adult Diabetes Stroke

0%

5%

10%

15%

20%

25%

30%

35%

40%

Cancer Heart Attack Adult Diabetes Stroke

Percentage of Americans Who Rate It Their #1 Health Concern

Percentage of Americans Who Rate It Their #1 Health Concern

Percentage of Americans Who Consider It “Highly Preventable”

Percentage of Americans Who Consider It “Highly Preventable”