Cancer

The Global Magnitude of the Problem of Cancer

Cancer afflict all the communities throughout the world. At present more than 11 million people are diagnosed with cancer and more than 7 million people die due to cancer every year, throughout the world. More than 30 million people are living with cancer at present. In term of incidence, the most common cancers are Lung cancer (12.3% of all cancer), breast cancer (10.4%) and colorectal cancer (9.4%). In terms of death from cancer the most common cancers is Lung cancer (17.8% of all deaths due to cancer).

For a disease, the relationship of incidence to mortality rate is an indication of prognosis. Similar incidence and mortality rate is indication of essentially fatal condition. That is why lung cancer accounts for most deaths from cancer (1.1 million) in the world annually, because its incidence and mortality rate is similar and it is invariably associated with poor prognosis. On the other hand for breast cancer appropriate management can be effective in avoiding fatal out come. That is why although it is second in term of incidence but in terms of mortality it is ranked 5^th .

The most important feature of the distribution of cancers between sexes is the predominance of lung cancer among males. Stomach, esophagus and bladder cancers are also common among males. Usually the difference in distribution between the sexes is attributed to the difference in exposure to the causative agents rather than difference in susceptibility. For example cancers of pancreas, colorectal cancer has insignificant sex difference. So, the incidence and mortality due to cancer is not effected by sex.

Burden of cancer in different countries is different from other countries due to difference in distribution . The total cancer burden is highest in the developed countries, due to high incidence of cancer associated with smoking and western lifestyle, i.e. cancer of lung , prostate and breast. On the other hand 25% of the cancers in the developing countries are due to infectious agents e.g. Liver cancer (hepatitis B), Stomach cancer (Helicobacter pylori), and cervical cancer (Human papilloma viruse). In western countries like USA recently there is a decline of incidence and mortality due to cancer. This is due to reduction in smoking prevalence, improvement in early defection techniques and advances in cancer therapy.

In USA there is no nationwide cancer registry. So the incidence of cancer is estimated on the basis of the National Cancer Institute’s Surveillance, Epidemiology and End Results (SEER) database and also from population data from the U.S. Census Bureau. 1.445 million new cases of cancer (766,860 men, 678,060 women) were diagnosed and 559,650 persons (289,550 men, 270,100 women) died from cancer in 2007. Cancer incidence has been declining in USA by about 2% each year since 1992.

Cancer is the second leading cause of death behind heart disease. Under age 85 years cancer has overtaken heart disease as the number one cause of death.

Cancer control (Secondary prevention)

Secondary prevention comprises the following measures:

(1) Cancer registration:

Cancer registration is a sine qua non for any cancer control programme. It provides a base for planning the necessary services and for assessment of the magnitude of the problem of cancer. Cancer registries are of two types: hospital-based and population based registries.

(a) Hospital-based registries: The hospital-based registry includes all patients treated by a particular institution, both inpatients and out patients. Registries collect data as recommended by WHO in the “WHO Handbook for Standardized Cancer Registers”. If follow-up is long-term, hospital-based registries can be of considerable value in the evaluation of diagnostic and treatment programmes and also for research. Since hospital population will always be a selected population, the use of hospital-based registries for epidemiological purposes is limited.

(b) Population-based registries: The best thing to do is to set up a “hospital-based cancer registry” and extend it to a “population-based cancer registry”. 2-7 million is the optimum size of base population for population based registry. The aim is to cover the complete cancer situation in a given geographic area. The data from such registries alone can provide the incidence rate of cancer and serve as a useful tool for initiating epidemiological enquiries into causes of cancer, surveillance of time trends and planning and evaluation of operational activities in all main areas of cancer control.

(2) Early detection of cases:

Cancer screening is the main weapon for early detection of cancer at a pre-invasive (in situ) or pre malignant (cancerous) stage. Effective screening programmes have been developed for cervical cancer (Papanicolaou smear, known as pap smear), breast cancer (mammography) and oral cancer. Like primary prevention, early diagnosis has to be conducted on a large scale. But it is possible to increase the efficiency of screening programmes by focusing on high-risk groups. but there is no point in detecting cancer at an early stage unless facilities for treatment and after care are available. Early detection programmes will require mobilization of all available resources and development of a cancer infrastructure starting at the level of primary health care, ending with complex cancer centers or institutions at state or national levels (tertiary health care).

(3) Treatment:

Treatment facilities should be available to all cancer patients. Some of the cancers are amenable to surgical removal, while some others respond favorably to radiation or chemotherapy or combination of both. Since most of the known methods of treatment have only complementary effect on the ultimate outcome of the patient, multi-modality approach to cancer control has become a standard practice in cancer centers. In the developed countries cancer treatment is geared to high technology. For those who are beyond the curable stage, the goal must be to provide pain relief. A largely neglected problem in cancer care is the management of pain. The WHO has developed guidelines on relief of cancer pain “Freedom from cancer pain” is now considered a right for cancer patients.

Cancer control (Primary Prevention)

Cancer control consists of a series of measures based on present medical knowledge in the fields of prevention, early detection through screening and population education, diagnosis, treatment, after care and rehabilitation, aimed at reducing the number of new cases, increasing the number of “cures” and reducing the invalidism due to cancer.

The basic approach to the control of cancer is through primary prevention and secondary prevention. It is estimated that at least one third of all cancers are preventable. If we analyze the causes of cancer it is seen that environmental factors are the most important in causation of cancer which are modifiable. Genetic factors which are not modifiable are responsible in small number of cases of cancer.

Primary prevention:

Cancer prevention till recently was mainly concerned with the early diagnosis of the disease (secondary prevention), preferably at a precancerous stage. Advancing knowledge has increased our understanding of causative factors of some cancers and it is now possible to control these factors in the general population as well as in particular occupational groups through population education and legislation.. They include the following:

1. Control of tobacco and alcohol consumption: Primary prevention offers the greatest hope for reducing the number of tobacco induced (tobacco related) and alcohol related cancer deaths. It has been estimated that control of tobacco smoking alone would reduce the total burden of cancer by over a million cancers each year globally. Some countries (e.g. Norway) have adopted ambitious programmes to eradicate tobacco smoking by the year 2000, which has given encouraging results.
2. Personal hygiene: Improvements in personal hygiene may lead t declines in the incidence of certain types of cancer, e. g. cancer cervix. Women with good personal hygiene have very low incidence of cervical cancer.
3. Radiation: Special efforts should be made reduce the amount of radiation (including medical radiation) received by each individual (patients, medical professionals, workers at nuclear reactors) to a minimum without reducing the benefits.
4. Occupational exposures :The occupational aspects of cancer are frequently neglected. Measures to protect workers from exposure to industrial carcinogens should be enforced in industries.
5. Immunization: In the case of primary liver cancer, immunization against hepatitis B virus prevent people from hepatocellular carcinoma (liver cancer).
6. Foods, drugs and cosmetics: These should be tested for carcinogens and legislation should be available to make these less harmful.
7. Air pollution: Control of air pollution is another preventive measure which can prevent lung cancer and many respiratory problems.
8. Avoidance of sun: Non melanoma skin cancers (basal cell and squamous cell) are induced by cumulative exposure to ultraviolet (UV) radiation. Reduction of sun exposure through use of protective clothing and changing patterns of outdoor activities can reduce skin cancer risk among Caucasians. Sunburns, in childhood and adolescence, are associated with increased risk of melanoma in adulthood. Sunscreens decrease the risk of actinic keratoses, the precursor to squamous cell skin cancer, but it may increase risk of melanoma. Sunscreens prevent burning, but this may encourage more prolonged exposure to the sun and may not filter out wavelengths of energy that cause melanoma.
9. Energy balance: Risk of cancer increases as BMI (body mass index) increases over 25 kg/m². Obesity increases risks for cancers of the colon, breast (female postmenopausal), endometrium, kidney (renal cell), and esophagus, although causality is not established. Relative risks of colon cancer are increased in obesity by 1.5–2.0 fold for men and 1.2–1.5 fold for women. Obese postmenopausal women have a 30–50% increased risk of breast cancer. A hypothesis for the association is that adipose tissue serves as a depot for aromatase (an enzyme) that facilitates estrogen production. Adiposity is also associated with poorer survival and increased risk of recurrence after treatment.
10. Treatment of precancerous lesions: Early detection and prompt treatment of precancerous lesions such as cervical tears, intestinal polyposis, warts, chronic gastritis, chronic cervicitis, and adenomata is one of the cornerstones of cancer prevention.
11. Screening for Cancer: Screening for cancer is one of the measure to prevent cancer. In the developed countries some of the cancer screening are compulsory e.g. screening for cervical cancer (Papanicolou smear known as pap smear) has virtually eradicated cervical cancer. But due to absence of this type of screening and poor personal hygiene in developing countries cervical cancer is still one of the commonest cancers in these countries.
12. Legislation: Legislation has also a role in primary prevention. The solution to cancer control problems is not to be found in research laboratories, but in legislatures. For example, legislation to control known environmental carcinogens (e.g. tobacco, alcohol, air pollution) is inadequate or only moderately enforced in a number of countries.
13. Cancer education: An important area of primary prevention is cancer education of general population. It should be directed at “high risk” groups. The aim of cancer education is to motivate people to seek early diagnosis and early treatment and also learn how to prevent cancer by changing lifestyle and food habits etc. Cancer organizations in many countries remind the public of the early warning signs (“danger signals”) of cancer. These are:

• A lump or hard area in the breast.

• A persistent cough or hoarseness.

• A change in a wart or mole.

• Excessive loss of blood during menstrual period or loss of blood outside the usual menstrual period.

• Blood loss from any natural orifice.

• A swelling or sore that do not heal.

• Unexplained loss of weight.

There is no doubt that the possibilities for primary prevention are many. Since primary prevention is directed at large population groups (e.g., high risk groups, school children, occupational groups, youth organizations) the cost can be high and programmes difficult to conduct . Primary prevention, although a hopeful approach, is still in its early stages. Major risk factors have been identified for a small number of cancers only and far more research is needed in that direction.

Causes of cancer

Cancer is a chronic disease. As with any other chronic diseases, cancer has a multifactorial etiology (cause). Carcinogens are the substances which can cause cancer to humans.

1. Environmental factors: Environmental factors are responsible for at least 90 per cent of all human cancers. The major environmental factors identified include the following:

a. Tobacco: Tobacco in various forms of usage (e.g. smoking, chewing, sniffing) is the major environmental cause of cancers of lungs, larynx, mouth, pharynx, esophagus, bladder, pancreas and also kidney. It has been estimated that cigarette smoking is responsible for more than one million premature deaths every year throughout the world in the form of cancer, respiratory problems and also in many other way. There is hardly any organ system which is not affected adversely due to cigarette smoking.

b. Alcohol: Excessive intake of alcoholic beverages is associated with esophageal and liver cancer. Some recent studies have suggested that beer consumption may be associated with rectal cancer. It is estimated that alcohol contribute to about 3 per cent of all cancer deaths in the world.

c. Diet: Dietary factors are also related to cancer. Smoked fish and meat is related to stomach cancer (consumption of smoked fish causes cancer), less intake of dietary fiber can cause intestinal cancer, excessive beef consumption can lead to bowel cancer and a high fat diet can lead to breast cancer. A variety of other dietary factors such as food additives and contaminants are also blamed to be carcinogenic. Diet rich in vitamins, minerals and antioxidants reduce the incidence of cancer.

d. Occupational exposures: These include exposure to benzene, cadmium, chromium, arsenic, asbestos, polycyclic hydrocarbons, vinyl chloride, etc. Many others remain to identified. The risk of occupational exposure is considerably increased if the individuals also smoke cigarettes. Occupational exposures are reported to account for 15 per cent of all human cancers. Occupation like road construction and handling of coal tar causes cancer of skin. Chimney sweepers are prone to develop prostate cancer.

e. Viruses : An intensive search for a viral origin of human cancers revealed that hepatitis B virus can cause hepatocellular carcinoma (liver cancer). The Epstein-Barr virus (EBV) is associated with 2 human malignancies, Burkitt’s lymphoma and nasopharyngeal carcinoma. Cytomegalovirus (CMV) is a suspected oncogenic agent of classical Kaposi’s sarcoma. Human papilloma virus (HPV) is the main suspect of cancer cervix. Main causative agent of cervical cancer is most likely a virus, due to the fact that it is almost non existence among Christian nuns who are not engaged in sexual intercourse. Whereas the incidence is very high among females with multiple sex partners. Hodgkin’s disease is also believed to be of viral origin. The human T-cell leukemia virus is associated with adult T-cell leukemia/lymphoma in United States and southern part of Japan .

f. Parasites: Parasitic infections can also increase the risk of cancer. Schistosmiasis in Middle East causes carcinoma of the urinary bladder.

g. Others: There are numerous other environmental factors such as sunlight, aeration, air and water pollution, medications (e.g. estrogen) and pesticides which are suspected to be related to cause cancer. Exposure to sun can cause skin cancer in white people, that is why skin cancer is most commonly seen in Australia and New Zealand.

h. Customs, habit and life styles: Customs, habits and lifestyles of people may be associated with an increased risk for certain cancers. The familiar examples are the demonstrated association between smoking and lung cancer, tobacco and betel chewing and oral cancer etc. Kangri cancer is seen in Kashmir. This is due to holding an earthen pot full of burning coal, in front of abdomen during winter months to keep the body warm. The skin around umbilicus is exposed to constant heat, which causes skin cancer.

2. Genetic factors: Genetic influences have long been suspected . For example, retinoblastoma occurs in children of the same parent. Certain people are more likely to develop cancer (leukaemia) than normal children. However, genetic factors are less conspicuous and more difficult to identify. There is probably a complex interrelationship between hereditary susceptibility and environmental carcinogenic stimuli in the causation of a number of cancers.

Cancer: a General understanding

Cancer can be regarded as a group of most serious diseases which are characterized by (1) abnormal growth of cells without control. (2) ability to invade nearby tissues and even to distant organs, by local invasion, through lymphatic system and blood. (3) the eventual death of patient it the tumor (cancer) has progressed beyond the stage when it can be successfully removed by surgery . Cancer can occur at any site of the body and it can involve any type of cells.

If cancer occurs in a tissue, the cells of the tissue starts growing abnormally fast. But the cells can not mature and because cells are not mature they cannot perform the function for which they are present in the body. For example if there is cancer of liver (hepatocellular carcinoma) the cancerous liver cells cannot perform functions of liver, but they consume the nutrition and due to large number and fast growing they consume large number of calories. This is the reason of weight loss in cancer. These immature cells keeps growing in number without any function and may spread to nearby tissues or to a distant site through blood. One cancerous cell is enough for spread to distant organ which keep growing very fast.

Cancer can be categorized into the following major categories:

1. Caremomas :They arise from epithelial cells which is the cell lining the surface of various organs like mouth, uterus, intestines, stomach, inner side of nose etc, This type may arise from skin also from skin epithelium .
2. Sarcomas :They arise from various cells which constitute connective tissues like bone, fat, fibrous tissues, bran tissue etc.
3. Lymphomas, myelomas and leukemias (blood cancer) arise from the cells of immune system as well as from bone marrow. Blood cancer or leukemia arise from bone marrow, because blood cells are formed in bone marrow.

In blood cancer (leukemia) white blood cells, whose main function is to fight with the invading microorganisms (bacteria, virus, fungus etc), starts growing abnormally rapidly in bone marrow but they are not mature. Because of immaturity they can not perform their primary function, which is to fight with invading microorganisms. And patient eventually die due to infection.

The term primary (cancer) tumor means cancer in the organ of origin, but secondary (cancer) tumor means the cancer which has spread to distant organ or to regional lymph nodes. When cancer cells multiply and reach a critical size cancer can be clinically evident as mass or ulcer in the particular area. Some time primary tumor can not be detected or found, but the secondary tumor became the main cancer. In this type of cases the primary tumor shrinks due some reason and become undetectable.