Epidemiology

CRC represents, in the world, 10.5% of all cancers in men and 10.3% in women. Table 1 shows about one million new diagnosed cases with large variations between different countries. In the world, there are 1 023 152 new cases of cancer and the number of deaths per year consist of about half of all new cases (528 978). The survival profile five years after diagnosis shows a relatively favourable prognosis for CRC (Table 2), although there are strong differences between developed and developing areas, and between single countries [3, 5-16].

The developed world accounts for 65% of all new cases. Colon cancer is more common in developed countries exhibiting westernised lifestyle practices. In the world, the incidence of CRC is at the 4th position for men and at the 3rd for women (Table 3).

There are different gender patterns between colon cancer and rectum cancer. In the colon the incidences of cancer are similar for both male and female. However, there is a male predominance for rectum cancer (30-50% higher than in women).

In countries with a Western lifestyle, CRC represents the second leading cause of death from cancer (after lung cancer) for men and the third for women (after breast and lung cancers).

In developed countries (as in Northern America, Japan, Eastern, Northern, Southern and Western Europe, Australia/New Zealand), GLOBOCAN 2002 notes that approximately 665 900 people develop CRC every year and that it kills 313 900 people per year. In the less developed countries, it ranks as the seventh leading cause of death among women and fifth among men. GLOBOCAN 2002 estimates 355 700 new cases occurred in 2002 and accounted for 214 200 deaths in developing countries.

Survival rates may be due to good treatment or early diagnosis or both. Table 4 shows TNM staging (data are expressed as percentage of total for each subsite) for CRC and the 5-year survival rate for each disease stage. In the world, the prevalence of CRC, five years from diagnosis, is estimated to be about 2 800 000 subjects in 2002 [17].

As indicated earlier, CRC presents quite a big gap between different economic ranges and different countries: the highest incidence rates for both men and women are in North America, Australia/New Zealand and Western Europe (48.2,44.4,42.9 per 100 000 men and 36.9, 32.8, 29.8 per 100 000 women

Table 1. Incidence, mortality and age standardised rates (ASR, world standard) for colorectal cancer (2002). Data source: GLOBOCAN 2002 database available via the internet at http://www-depdb.iarc.fr/globocan/GLOBOframe.htm [Accessed 2005 March]

Table 1. Incidence, mortality and age standardised rates (ASR, world standard) for colorectal cancer (2002). Data source: GLOBOCAN 2002 database available via the internet at http://www-depdb.iarc.fr/globocan/GLOBOframe.htm [Accessed 2005 March]

New cases

ASR (W)

Deaths

ASR (W)

m

f

m

f

m

f

m

f

World

550 465

472 687

0.83

0.59

278 446

250 532

0.42

0.30

More developed regions

353 390

312 341

1.67

1.09

159 914

153 980

0.71

0.50

Less developed regions

196 037

159 664

0.42

0.30

118 025

96 184

0.25

0.17

Eastern Africa

4019

2997

0.25

0.17

3723

2761

0.21

0.13

Middle Africa

627

951

0.09

0.13

587

887

0.08

0.13

Northern Africa

3150

2707

0.21

0.17

2935

2525

0.17

0.13

Southern Africa

1553

1644

0.46

0.38

1056

1106

0.30

0.25

Western Africa

3430

2605

0.21

0.13

3224

2460

0.17

0.13

Caribbean

2610

3032

0.59

0.63

1633

1945

0.38

0.38

Central America

3677

3870

0.30

0.29

2136

2310

0.17

0.17

South America

22 159

24 125

0.67

0.59

10 936

12 147

0.33

0.29

Northern America

94 745

88 728

1.84

1.34

33 421

32 939

0.63

0.46

Eastern Asia

155 157

107 578

0.80

0.50

75 281

56 250

0.38

0.25

South-Eastern Asia

23 760

21 119

0.50

0.38

15 063

13 362

0.33

0.25

South-Central Asia

26 940

20 254

0.17

0.13

18 248

13 525

0.13

0.09

Western Asia

7544

7226

0.46

0.38

4583

4370

0.26

0.21

Central and Eastern Europe

55 408

56 814

1.25

0.83

36 602

38 597

0.80

0.51

Northern Europe

29 102

26 213

1.55

1.09

13 999

13 483

0.71

0.50

Southern Europe

43 586

35 575

1 .46

0.96

21 661

18 163

0.71

0.46

Western Europe

64 886

60 122

1.76

1.21

29 968

30 823

0.79

0.58

Australia/New Zealand

7897

7002

2.00

1.51

3247

2786

0.79

0.58

Melanesia

149

78

0.30

0.17

101

54

0.21

0.09

Micronesia

30

22

0.63

0.46

19

14

0.38

0.30

Polynesia

31

26

0.59

0.42

20

18

0.38

0.29

Table 2. Estimated age-adjusted colorectal cancer survival (%) by country/area

Table 2. Estimated age-adjusted colorectal cancer survival (%) by country/area

Males

Females

United States

66

65

Eastern Europe

35

36

Western Europe

56

53

Japan

65

58

All developed areas

56

54

South America

50

50

India

28

31

Thailand

37

37

Sub-Saharan Africa

13

14

All developing areas

39

39

respectively), while the lowest rates are registered in Central and Western Africa, and in South Asia (2.3, 5.1, 4.7 per 100 000 men and 3.3, 3.5, 3.5 per 100 000 women respectively) (Fig. 1).

There is even a variation for the site of the neoplasm (colon/rectal). In fact, in "high-risk countries", 2/3 of all cases are represented by a colon cancer and 1/3 by a rectal one [17]. In contrast, in "low-risk countries", the risk for the two sites is the same. The incidence variation in different sites could be explained by different exposure to risk factors. There is a direct correlation between CRC and diets high in red meat, animal fats, alcohol and a low use of fibre. Some epidemiological studies note that a sedentary life and excess body weight can increase the risk of CRC.

Research evidence reveals that the incidence in groups of migrants from low to high risk countries tends to increase to the rates of the host countries within the first or second generation, or, even as early as within the migrating generation itself. The geographic location of the country of origin, age at migration, time of residence in the adoptive country and the extent of cultural assimilation all influence the level and speed of the increase. There are several examples of this such as the mortality of Japanese immigrants in the United States, which is significantly higher than that among the Japanese in Japan [18, 19]; and by the early 1970s the Japanese in Hawaii had a mortality similar to that of whites in Hawaii [20, 21]. Also, in Chinese people migrating to the USA, mainly from one province in China, the mortality rate among the first generation of migrants was 2.7-5.6 times higher than found in that province [22, 23].

Table 3. Incidence (new cases) by sex and cancer site worldwide, 2002

Males

No. of new cases

Females

No. of new cases

Lung

965 241

Breast

1 151 298

Prostate

679 023

Cervix uteri

493 243

Stomach

603 419

Colon/rectum

472 687

Colon/rectum

550 465

Lung

386 891

Liver

442 119

Stomach

330 518

Oesophagus

315 394

Ovary

204 499

Bladder

273 858

Corpus uteri

198 783

Oral cavity

175 916

Liver

184 043

N-H lymph.

175 123

Oesophagus

146 723

Leukaemia

171 037

Leukaemia

129 485

Another example describes the incidence differences in Israeli Jews according to place of birth [24]:

• as well as, in Israeli non-Jews (4.6/100 000). About 20-30% of all large bowel cancers are in the rectal site, 20-26% in the sigma, 10% in the descending colon, 13% in transverse colon and 15-20% in the proximal colon (ascending colon and appendix).

Subsite distributions of colorectal malignancies indicate that approximately 70% of colorectal malignancies are localised in the distal or left large bowel (between the splenic flexure and the lower rectum) [25]. Several studies, however, showed a tendency for a shift to proximal sites of cancer distribution, with right-sided cancers becoming more prevalent and left-sided lesions less prevalent [26-30]. These stud ies are not without controversy [31,32]. If the "rightwards shift" is a true phenomenon, this might represent one more reason for abandoning sigmoidoscopy and favouring pancolonoscopy as the technique of choice for screening individuals at risk of CRC.

It remains unclear if this is a true biological phenomenon or simply an artefact due to a variety of factors including the lack of agreement on the most appropriate division of the colorectum into anatomical subsites [1, 2]. Other possible explanations for the different distribution pattern of colorectal malignancies into right and left colonic segments might include: the impact of environmental risk factors such as diet and lifestyle, a different frequency of hereditary colorectal neoplasm (which are characterised by an increased frequency of right-sided lesions) [33] and a more or less extensive use of colonoscopy.

Males

Females

Australia/New Zealand Northern America Japan Western Europe Northern Europe Southern Europe Eastern Europe South America Carrbean -Micro/Polynesia China

South-Eastern Asia Western Asia Southern Africa Central America Melanesia Eastern Africa Northern Africa Western Africa South-Central Asia Middle Africa

ASR(W) CRC incidence per 100 000

Fig. 1. Age standardised (world population) incidence rates for colorectal cancer. Data shown per 100 000 by sex. Data source: GLOBOCAN 2002 database available on the internet at http://www-depdb.iarc.fr/globocan/GLOBOframe.htm [Accessed 2005 March]

In a recent study Ponz de Leon et al. [34] examined the pattern of incidence, subsite distribution and staging in the 15-year experience of a specialised cancer registry (Modena, Italy). They found that:

1. There was a general increase in the incidence of colorectal neoplasms during the registration period. This increase was observed in both sexes, though incidence rates in women remained significantly lower than in men.

2. Tumours were appreciably more frequent over the age of 50 years.

3. Tumours stage I, II and III showed a significant increase in incidence over time (with a significant improvement of 5-year survival). In contrast, the incidence of more advanced disease (stage IV) remains quitestable.

4. There was a gradual increase in cancer incidence in all colonic segments, while rectal lesions tended to decline.

The more favourable staging at diagnosis is presumably related to the wider use of colonoscopy. This, in turn, can be attributed to an increased attention of patients and doctors towards the screening and early detection of this common neoplasm.

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