Technically speaking, cancers are a variant of the diseases described above in which the disease spreads locally or the abnormal cells travel through the blood and lymphatic system to continue the abnormal growth at other parts of the body.
On the other hand, tumours referred to as benign do not grow uncontrollably, do not invade neighbouring tissues and do not spread through the body.
Healthy cells control their own growth and would destroy themselves if they become unhealthy.
Cell division is a complex process that is normally tightly regulated. Cancer happens when problems in the genes in a cell prevent these controls from working. Genes are very tiny inheritable chemical ‘structures’ in a cell that directs various growth and development processes in the cell and hence the body. These problems with genes may be from damage to the gene or may be inherited.
Determining what causes cancer is complex and it is often difficult to point to a specific cause for a specific cancer. Many things are known to increase the risk of cancer including tobacco use, infection, radiation, lack of physical activity, poor diet, obesity and environmental pollutants.
These can directly damage genes or combine with existing genetic defects within cells to cause disease. A small percentage of cancers say about 5-10% are entirely inherited.
Cancer can be determined in a number of ways, including the presence of certain signs and symptoms, screening tests, or medical imaging. Once a possible cancer is detected, it is confirmed by microscopic examination of a tissue sample and is usually treated with chemotherapy, radiation therapy or surgery or any combination of these three options. The chosen method of treatment or combination would depend on the extent of disease and the patient’s condition. The chances of surviving the disease vary greatly by the type and location of the cancer and the extent of disease at the start of treatment. While cancer can affect people of all ages, a few types of cancer are more common in children and the risk of developing cancer generally increases with age. In 2007, cancer caused about 13% of all human deaths worldwide (7.9 million) and rates are rising as more people live to an old age and lifestyles changes in the developing world.
Cancers are classified by the type of cell that the tumuor resembles which is therefore presumed to be the origin of the tumuor. These types include:
• Carcinoma, which are cancers derived from epithelial cells. This group includes many of the most common cancers, particularly in the aged, and includes nearly all those developing in the breast, prostate, lung, pancreas and colon.
• Sarcoma are cancers arising from connective tissue such as bone, cartilage, fat, nerve and each of these develop from cells originating in what is referred to as mesenchymal cells outside the bone marrow.
• Lymphoma and leukaemia: These two classes of cancer arise from haematopoietic or blood-forming cells that leave the bone marrow and tend to mature in the lymph nodes and blood respectively.
• Germ cell tumuors are cancers derived from pluripotent cells most often showing up in the testes or the ovary. Pluripotent cells have the capacity to develop into various fetal and adult tissues.
• Blastoma: cancers derived from immature ‘precursor’ cells or embryonic tissue tend to occur more commonly in children.
SIGNS AND SYMPTOMS
Cancer symptoms are usually non-specific which means that many other illnesses also show the same symptoms and signs. Cancer symptoms can be divided into three groups:
• Local symptoms are restricted to the site of the primary cancer and these could include lumps or swellings, bleeding from the skin, mouth or anus, wounds and pain. Initial swellings of tumuors may be painless but advanced cancers can be really painful.
• Metastatic symptoms are due to the spread of cancer to other locations in the body. These include enlarged lymph nodes which can be felt under the skin or enlargement of the liver or the spleen which is felt in the abdomen.
The spleen is an organ situated in the upper left region of the abdomen involved in the immunological defense of the body. Other symptoms include the pain or fracture of affected bones and symptoms involving the body’s nerves.
• Systemic symptoms are those symptoms that occur due to distant effects of the cancer but are not related to the direct or metastatic spread of the cancer. Some of these symptoms include weight loss due to poor appetite and body wasting, fatigue, excessive sweating especially at night, anaemia and other non-specific conditions that may be mediated by the immunological or hormonal signals from the cancer cells.
It is almost always impossible to prove exactly what caused a cancer in any individual because most cancers have multiple causes. For instance, a heavy tobacco smoker who develops lung cancer would blame the tobacco but all of us have a small chance of developing lung cancer due to air pollution and radiation.
As stated earlier most of the causes of cancer are environmental and these include factors such as tobacco, diet, obesity, infections, radiation, stress, lack of physical activity and environmental pollutants.
Many chemicals have been known to have carcinogenic effects. Aside tobacco that has been mentioned above, other chemicals include alcohol, exposure to benzene at workplaces and the inhalation of asbestos fibers.
DIET AND EXERCISE
Diet, physical inactivity and obesity are related to approximately about 30% of cancer cases. Physical inactivity is believed to contribute to cancer risk not only through its effect on body weight but also through negative effects on immune system and the network of hormones.
Diets that are low in vegetables, fruits and whole grains, and high in processed or red meats are linked with a number of cancers. A high salt diet is linked to stomach cancer and aflatoxin B1, a frequent food contaminant with liver cancer. Our local kokonte sometimes gets contaminated with aflatoxins.
About a fifth of cancers are linked to infections and the agents include viruses, bacteria and parasites. Cervical cancer is caused by human papillomavirus and liver cancer can be caused by hepatitis B and C viruses.
Leukaemias and Kaposi Sarcoma can also be virus-induced. Stomach cancer is linked to a bacterium called helicobacter pylori and a parasite called schistosoma haematobium is known to cause cancer of the urinary bladder.
About 10% of invasive cancers are related to radiation exposure. Sources of radiation include medical imaging and radon gas. Non-ionizing radio frequency radiations from mobile phones, electric power transmission and other similar sources have been described by the WHO as a possible carcinogen.
About 5-10% of all cancers have been linked to factors that are inherited. Some cancers in this category include breast cancer, ovarian cancer, bone cancer, brain tumours, colon cancer, stomach cancer, testicular cancer, leukaemias and retinoblastoma in children.
A related factor to heredity causes is the level of hormones. Breast and ovarian cancers are believed to be linked to inherited levels of high female hormones while high levels of male hormones in men of African ancestry are believed to be a factor in the high level of prostate cancer in this group.
Cancer prevention is defined as active measures undertaken to decrease the risk of cancer. The vast majority of cancer risk factors are due to environmental (including lifestyle) factors, and many of these factors are controllable. More than 30% of cancers are considered preventable by avoiding risk factors including tobacco, obesity, inappropriate diet, physical inactivity, alcohol, sexually transmitted infections and air pollution.
However, not all environmental causes can be prevented such as background radiation. Dietary recommendations to reduce the risk of developing cancer includes reducing intake of foods and drinks that promote weight gain such as energy-dense foods and sugary drinks, eating mostly foods of plant origin, limiting intake of red meat and avoiding processed meat, limiting consumption of alcoholic beverages and reducing intake of salt and avoiding mouldy cereals.
Vaccination is helpful in preventing certain types of cancer such as hepatitis B vaccine and vaccine against human papillomavirus which causes cervical cancer. Screening tests are available for certain types of cancer but not possible for all types of cancer.
A screening test would make good medical sense when it causes little harm and there is ready and accessible treatment for the disease that is being screened. Screening tests can be done for cervical cancer, prostate cancer, breast cancer, colon cancer etc.
Most of the factors linked to the causation of cancer are lifestyle-related and hence preventable and the adherence to these recommended interventions takes a lot of discipline so the earlier one begins implementing them, the earlier one can get used to them and the easier it becomes.