git - community slides lec 1.ppt

8/10/2019 GIT - Community slides lec 1.ppt

1/18

1

Epidemiology and prevention of

colorectal cancerICD9: 153, 154


2/18

2

1. Significance The second leading cause of cancer death in men & women (The

# 1 is..). It accounts for 10% of all cancer deaths in theUSA.

More lives are lost each year to colorectal cancer than tobreast cancer and AIDS combined.

it accounts for nearly half of the diagnosed new cases ofcancer.

The incidence and mortality of colorectal cancer (CRC) showincreasing tendency worldwide.

Compared to 2000 data, the new cases in 2007 approximate1,200,000 and the death cases 630,000, a total increase of

27% and 28% and an annual increase of 3.9% and 4.0%,respectively.

The overall 5-year survival rate for CRC is 61%; 91% for CRCin local stage.


3/18

3

2. Pathophysiology Not well understood Some research suggests delay transit of fecal material.

Related to: Low fiber diet intake

Lack of physical activity

Predominant cell type is adenocarcinoma (96% of all cases).


4/18

4

3. Descriptive epidemiology

a. High-Risk Groups

Gender: 44% Higher for men Race: 15% higher for Blacks than for Whites. Age: Incidence rises sharply after the age of 50 years;

>80% of diagnosed cases of colorectal cancer occurin patients older than 55 years.

The mean age at diagnosis is 62 years. SES: People in higher socioeconomic groups. Certain genetic and medical conditions Predispose to CRC include:

First kin relatives

Familial polyposis

Inflamatory bowel disease (e.g. Ulcerative colotis, Crohns ).


5/18

5

b. Geographic distribution Worldwide,

CRC is highest in developed countries in North

America, Northern and Western Europe, and NewZealand.

Extremely low in Japan; Japanese immigrants to theUSA have similar rates as the Americans.

In USA, CRC is highest in Northeast and North-Centralstates, lowest in Western and Southwestern states.


6/18

6

c. Time trends

The incidence of CRC varies regionally and changes over thetime.

a. In previously identified high-incidence areas, there arethree tendencies:

The incidence keeps rising such as in UK, The incidence is stable such as in New Zealand, and The incidence tends to decrease such as in US and

Western Europe.

b. In previously identified low-incidence areas, the incidenceof CRC is increasing, such as in Japan, Hong Kong,Singapore,

Hungary, Poland, and Puerto-Rico, especially inJapan, where the incidence increases the fastest.


7/187

Since 1991, the average increase in mortality of CRC is 4.7%every year.

The increasingnumber of femalepatients and the shift of thetumor location to the right side are also the trends noticed forCRC in recent years.


8/188

4. Risk Factorsa. Magnitude of risk factors

Modifiable risk factors for colorectal cancer, USMagnitude Risk Factor Pop.Att.Risk (%)Strong RR>4 None -Moderate RR 2-4 None -Weak RR


9/189

Relative Risk= Risk of disease/death in the exposed populationRisk of disease/death in the unexposed population

Population Attributable Risk is: Proportion of a disease in a

population that is associated (attributed to) a certain risk factor.

b. Population Attributable Risk

Up to one-half of CRC may be related to diet.

Within this proportion, it is estimated that 15%-25% of CRC may berelated to fat intake and that 25%-35% may be related to lowintake of fruits and vegetables

An estimated 32% of CRC may be related to physical inactivity.

P ti d C t l M


10/1810

5. Prevention and Control Measuresa. Prevention

The overwhelming evidence indicates that primary prevention of coloncancer is feasible.At least 70% of colon cancers may be preventable by moderatechanges in diet and lifestyle.

i. Diet and Nutrition

There is convincing evidence from epidemiological and experimentalstudies that dietary intake is an important etiological factor incolorectal neoplasia.

The precise mechanisms have not been clarified, yet several lifestyle

factors have a major impact on colorectal cancer development.

- Fats and meats

US Nurses Health Study: In 1990 Willett et al published the results from follow up of

88,751 women aged 34-59 years who were without cancer orinflammatory bowel disease at recruitment.


11/1811

Consumption of animal fat was found to be associated withincreased risk of colon cancer, after adjustment for total energyintake.

RR in the highest compared with the lowest quintile = 1.89 (95%confidence interval 1.13 to 3.15) (P=0.01).

No association was found with vegetable fat.

RR in women who ate beef, pork, or lamb as a main dish every day

was 2.49 (1.24 to 5.03) compared with women reportingconsumption less than once a month.

The study data supported:- the hypothesis that a high intake of animal fat increases the

risk of colon cancer, and

- the existing recommendations to substitute fish and chicken formeats high in fat.


12/1812

- Fiber Fiber has many components commonly grouped into:insoluble, non-degradable constituents (mainly found in cereal fiber)and soluble, degradable constituents, such as pectin and plant gums

(mainly found in fruits and vegetables). Epidemiological studies have reported differences in the effect of

these components.

Many studies, however, found no protective effect of fiber in

cereals but have consistently found a protective effect of fiber invegetables and perhaps fruits.

This might reflect an association with other components of fruitsand vegetables, with fiber intake acting merely as an indicator ofconsumption.

Recent epidemiologic studies tended not to support a stronginfluence of fiber; instead, some micronutrients or phytochemicalsin fiber-rich foods may be important. Folate (and methionine) isone such nutrient that has received attention lately and is beingstudied in randomized intervention trials.


13/1813

International and migrant population data indicate that asubstantial reduction in the incidence of CRC could be achieved in10 years through dietary changes alone: By increasing per capita consumption of fiber from fruits and

vegetables to 20-30 grams/day. By decreasing per capita consumption of fat to below 30% of

total calories.

ii. Vitamin DA scientific review of literature found that vitamin D was beneficialin preventing colorectal cancer. There is an inverse relationshipwith blood levels of 80 nmol/L or higher. These levels areassociated with a 72% risk reduction compared with lower than 50nmol/L levels.

iii. Chemopreventive agents (aspirin and postmenopausal estrogens):

There is much evidence suggesting an inverse relationship betweenaspirin or non-steroidal anti-inflammatory drug (NSAID)consumption and CRC incidence and mortality.


14/18

14

However, NSAID consumption is not problem-free; 1997 datashow 107,000 hospitalisations and 16,500 deaths due to NSAIDconsumption in the U.S. alone.

Therefore, drugs that have more acceptable side-effect profilesare required.

Cyclo-oxygenase (COX)-2-specific inhibitors, which have an

improved safety profile, seem to be well-suited drug candidatesfor CRC prevention.

Pharmacology and genetics are collaborating to develop newchemoprevention agents designed to affect molecular targets

linked to specific premalignant or predisposing conditions.


15/18

15

iv. Physical inactivity, and to a lesser extent excess body weight,are consistent risk factors for colon cancer.

v. Exposure to tobacco products early in life is associated with ahigher risk of developing colorectal neoplasia.


16/18

16

Screening for CRC

The evidence is convincing that there are substantial benefits toscreening in asymptomatic adults.

U.S. Preventive Services Task Force (USPSTF) recommendsscreening for colorectal cancer in all asymptomatic adults from 50to 75 years of age.

Balancing the small benefit and potential increased harms, theUSPSTF does not recommend routine screening in asymptomaticadults from 75 to 85 years of age and

recommends against screening in asymptomatic adults older than 85years of age who have previously been adequately screened.


17/18

17

screening for colorectal cancer with: High-sensitivity fecal occult blood testing (fecal DNA and fecal

immunochemical testing)

sigmoidoscopy, or colonoscopy

Modeling evidence suggests that population screening programsbetween the ages of 50 and 75 years using any of the following 3regimens will be approximately equally effective in life-years

gained, assuming 100% adherence to the same regimen for thatperiod.


18/18

git - community slides lec 1.ppt

Documents