Incidence of common cancers
Cancer is a common disease affecting a third of the population
 in their life time There are 250 000 new cases diagnosed per year65% of cancer affects the> 65 age group Common cancers are different for different age groups (adults, teenagers children) Smoking and diet are the main environmental etiological factors (thought to be responsible for a third of cancer cases each

Cancer incidence by age and gender

Common cancers in adult 50% of adult cancer involves the big four: breast, prostate, lung, large bowel.Remember that the incidence of a cancer is not the same as the death rate cancer

 Incidence data can be expressed as the number of new cases per 1000 as a percentage There is a different incidence of certain cancers in men and women commons cancers in teenagers testicular cancer.brain tumours melanoma leukaemia common cancers  in children the risk of cancer in childhood < 15 years) is 1 in 500 in the UK commonly these cancers are  haematological: 25% of childhood cancers are acute lymphocytic leukaemia ALL incidence of Hodgkin's lymphoma peaks in teenagers brain and spinal cord: eg astrocytoma and primitive neuroectodermal tumour

 Embryonal tumours occurs in different parts and referred to as blastoma eg. medulloblastoma (brain), nephroblastoma (Wilms tumour), retinoblastoma .Bone tumours: osteosarcoma and Ewing's sarcoma. Bone tumour incidence peaks at14-15 years Cancer incidence by geographical region Different cancers have different in different countries and In different ethnic groups  • Breast cancer: much less common in the third world than in developed incidence is highest in the west and second-
generation immigrants from ares of low  incidence (they acquire the elevated risk of their new country

 Hepatocellular carcinoma: most common where hepatitis B infection is East,sub-SaharanAfrica) regardless of race. Iron 
overload and aflatoxin also contribute in these regions

Stomach cancer:common in Japan and Chile. First-generation immigrants to the west retain this high rate but second-generation immigrants adopt the lower rate  of their new country

 Colon cancer: westernised countries with low-fibre diets have increased colon cancer• Prostate cancer: highest in Afro-Caribbean people and lowest in Japan

 Oesophageal cancer: common in China, USSR and poor nations. The reason may be dietary• Epstein-Barr virus: spread around the world,but Burkitt's lymphoma is an Afrocan  disease, and its distribution corresponds to regions where malaria is endemic  Immigrants to Africa are susceptible,as are the native Black people

 Skin cancers: (notably melanomas) are commonest in light-skinned people who have heavy sun exposure at low latitudes and/or high altitudes

 Cervical cancer: incidence follows that of STDs (aetiological agent is HPV).  it may be less common in areas where men are circumcised

 Squamous cell carcinoma of the bladder: caused by schistosomiasis and so is common in endemic areas(eg Egypt) Changes in cancer incidence in Europe 
what are the Factors impacting on incidence of cancer

 Behavioural factors
 Women starting to smoke in the  (increase in lung cancer)• Sunbathing and tanning became fashionable (increase in melanoma

Environmental factors
 exposure to Asbestos ,Aniline dyes 

what are diagnostic tests

introduction of PSA as a test for occult and asymptomatic prostate cancer Screening may be  increase incidence (by detection of early tumour and may be  decrease incidence (by detection of precursor lesions that can be treated before the tumour develops eg colorectal polyps, carcinoma in situ of the cervix there is a variable lag period before the effects of changes in behaviour or environmental; are seen

 Implementation of new diagnostic tests or screening programmes may have much rapid impact on the incidence figures increasing incidence of cancer

 Increase in incidence kidney non Hodgkin's lymphoma breast_leukaemia  ovary

 decreasing in the following cancers:large bowel pancreas bladder .stomach Lung ,Cervi

Some important cancer incidence
 Stomach Cancer

The incidence of stomach cancer varies significantly among differrent regions of the world The age-adjusted incidence is highest in Japan . In comparison. the rates are much lower in North America, eastern and northern Africa, and South and Southeast Asia

The difference in risk by country is presumed to be due to differences in dietary factors and in the incidence of infection with Helicobacter pylori, which is known to play a major role in gastric cancer development for­ fortunately. a steady decline is being observed in the incidence and mortality rates of gastric cancer. This may be related to improvements in preservation and storage of foods
Breast cancer
The incidence of breast cancer is high in all of the most highly developed regions except japan. including the United States and Canada. Australia, and Northern and Western Europe. In comparison, the rates are relatively low in sub-Saharan Africa (except South Africa) and Asia

The highest breast cancer incidence is in the United Slates and the lowest is in china Al­though breast cancer has been linked to cancer susceptibility genes, mutations in these genes account for only 5 to 10 %of breast tumors, suggesting that the wide geographic variations in breast cancer inci­dence are not due to geographic variations in the prevalence of these genes. Most of the differences, therefore, are attributed to differences in reproductive factors. diet, and other environmental differences. Indeed
 Overall the incidence of breast cancer is rising in most countries

 Colon and Rectal Cancer

The incidence of colon and rectal cancer is higher in developed countries than developing countries

The incidence rates are high­est in Australia/New Zealand. North America, and Northern and Western Europe

 In contrast, the incidence is relatively low in North Africa, South America, and Eastern. South eastern. and Western Asia. These geographic differences are thought to reflect environmental exposures and are presumed to be mainly dietary difference

liver cancer

In contrast to colon cancer. 80% of liver cancers occur in developing countries. The incidence of liver cancer is especially high in china and other countries  in Eastern Asia  . while it is relatively low in North and South America and Europe  World wide

The ma­jor risk factors for liver cancer are infection with hepatitis viruses and consumption of foods contaminated with aflatoxin
Hepatitis B Immunization in children has recently been shown to reduce the incidence of hepatitis infection In China. Korell, and West Africa, Whether this will translate into a reduction in the incidence in liver cancer in these regions will soon be determined
Prostate cancer
The incidence of prostate cancer is dramatically higher in North America than in china. Japan. and the rest of Asia
 A considerable part of the international differences in prostate cancer incidence is thought to reflect differences in diagnostic practices

The introduction of PSA screening has led to a significant increase in the diagnosis of prostate cancer in the United States
Esophageal cancer

Geographic variations in the incidence of esophageal cancer are also striking. The highest incidence of this cancer is in Southern Africa and China The risk is 15-fold lower in men in North, Middle, and West Africa and 5-fold lower in men in Europe and North America

These geographic differences are attributed to nutritional deficiencies and exposures to exogenous carcinogens. Esophageal cancer in North America and Europe is attributed to tobacco and alcohol use The mortality rates of different cancers also vary significantly among countries
This is attributable not only to variations in inci­dence but also to variations in survival after a cancer diagnosis. These 5-year sur­vival rates are influenced not only by treatment patterns but also by variations in cancer screening practices. which affect the stage of cancer at diagnosis. For example. the 5-year survival rate of stom­ach cancer is much higher in Japan, where the cancer incidence is high enough to warrant mass screening and is presumed to lead to earlier diagnosis

In the case of prostate cancer, the moralily rates diverge much less than the incidence rates among countries. Sur­vival rates for prostate cancer are much higher in North America than in developing countries It is possible that the extensive screening practices in the United States allow discov­ery of cancers at an earlier, more curable stage; however. it is also possible that this screening leads to discovery of more latent, less biologically aggressive cancers. which may not have caused death even if they had not been identified. in summary the incidence rates of many common cancers vary widely by geography This is due in part to genetic differences. including racial and ethnic differences. It is due also in part to dif­ferences in environmental and dietary exposures, factors that can potentially be altered. Therefore. establishment of regional and international databases is critical to improving our understanding of the etiology of cancer, and will ultimately assist in the initiation of targeted strategies for global cancer prevention. Furthermore, the monitoring of cancer mortality rates and 5-year. cancer specific sur­vival rates will identify regions where there are inequities of health care, so that access to health care can be facilitated and guidelines for treatment can be established

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