What is Cancer?
Cancer is a term used for a group of potentially life-threatening diseases during which normal cells become abnormal, divide without control and invade other tissues.
‘Tumour’ is the collective term used for the growths or lumps caused by the abnormal multiplying of cells. Depending on their ability to spread or invade other body tissue, tumours can be ‘benign’ or ‘malignant’. Malignant tumours tend to spread, whilst benign tumours mainly remain localised.
Why does cancer start?
Normal cell division is required for the generation of new cells during growth and to replace old or injured cells as they die. The normal cell cycle is a critical process that a cell undergoes in order to copy itself exactly.
Most cancers are caused by mutations that impair the controls and signals that the body uses to regulate a cell’s cycle of growth and division. Cells that progress through the cell cycle unchecked may eventually form tumours. Where masses of cells rapidly grow and divide uncontrollably, they may develop the ability to spread and migrate throughout the body.
How common is cancer?
Globally, approximately 12 million new cases of cancer are diagnosed annually. According to Dr Carl Albrecht, the head of research at the Cancer Association of South Africa (CANSA), the current prevalence in South Africa is not really known, but it is estimated that 1 in 4 males and 1 in 6 females in South Africa will develop cancer. In South Africa, more than 100 000 new diagnoses are made every year, and the South African cancer survival rate is 6/10. Cancer kills more people than TB, malaria and HIV/AIDS combined.
What causes cancer?
Only 5-10% of all cancer cases can be attributed to genetic defects, whereas the remaining 90-95%have their roots in the environment and lifestyle. According to CANSA, the following factors contribute to the development of cancer:
- Age: Longevity and urbanisation are the two factors that play a leading role in the global upsurge of cancer. As cancer cells take time to develop, the longer you live, the higher your chances of developing cancer.
- Smoking: World-wide, the most common cause of cancer is smoking. About 1 out of every 3 cancer cases is due to smoking.
- Viruses: Viruses, such as hepatitis B, which causes liver cancer and human papillomavirus, which leads to cervical cancer, cause about 20% of cancers, although vaccines for both are available. South Africa initiated vaccination of children against Hep B in 1996 and this should help to eliminate liver cancer in South Africa within the next 20 years.
- Chemicals: Chemicals are responsible for approximately 15% of cancer cases. For example, man-made chemicals such as Bisphenol A (BPA), which is used to make certain types of plastics, are strongly linked to breast cancer.
- Water: Toxic water can cause cancer. For example, water in the Tlokwe municipality (Potchefstroom) has been found to contain radioactive elements such as uranium. Excessive exposure to uranium is associated with certain types of cancer, including leukaemia.
- Alcohol: About 3% of European cancer cases in women are associated with alcohol consumption, compared with 10% in men. Drinking moderately (1 to 2 units a day) appears to have no impact on cancer development. A higher intake can, however, be problematic and binge drinking is more detrimental due to the sudden spikes of alcohol which cause more damage than constant exposure.
- Sunlight or ultraviolet exposure: Sun cancers, such as malignant melanomas, account for about 5% of cancer cases.
- Genes: About 10% of cancer cases are linked to DNA.
- Obesity and diet: Being excessively overweight is strongly associated with the development of 15-20% of cancers.
How is cancer linked to the metabolic syndrome?
The metabolic syndrome is associated with many physiological changes, including insulin resistance, resulting in high levels of insulin in the blood stream, central obesity, increased oestrogen levels and increases in many inflammatory substances. These factors are known to lead to the development of cancer.
A number of studies published in the Metabolic Syndrome and Cancer Project (Me-Can) explain the association between the metabolic syndrome as a whole and its individual components with the risk of cancer.
- Higher glucose levels are associated with increased risk of liver, gallbladder, respiratory and thyroid cancer and multiple myeloma in men, as well as pancreatic, bladder, endometrial, cervical and stomach cancer in women.
- A higher composite metabolic syndrome score (i.e. the more components present in an individual) has been linked to an increased incidence of bladder cancer in men and post-menopausal breast cancer in women.
- High triglycerides have been shown to increase the risk of colon, respiratory tract, kidney and thyroid cancers and melanomas in men, as well as respiratory, cervical and non-melanoma skin cancers in women.
- Hypertension (high blood pressure) is associated with an increased risk of multiple cancers in men and women.
- Cholesterol may have direct effects on tumour cells and may interact with androgen and oestrogen signalling tumours.
- Hyperinsulinaemia: high levels of insulin could be a major player in cancer, not just as an indicator of insulin resistance, but actually as a hormone driving cancer growth.
How are excess weight and cancer linked?
Many scientific studies have demonstrated that obesity is associated with an increase in both the development of many common types of cancer, as well as an increase in cancer-related deaths.
Cancers associated with obesity include oesophageal, pancreatic, colo-rectal, breast, endometrial, renal, thyroid and gallbladder. The biggest risk appears to occur in breast, colorectal, endometrial and oesophageal cancers.
Fat tissue (adipose tissue) is an active hormonal organ. Excess adipose tissue influences the risk of developing cancer via a variety of mechanisms, including its effect on hormones, increased insulin levels (hyperinsulinaemia), increased cell proteins (cytokines), systemic inflammation and the body’s altered immune response.
Obese adipose tissue also results in an imbalance of a variety of substances that would normally control cell division. Adipokines (substances secreted by fat cells) that limit cell growth and regulate natural cell death are supressed (e.g. adiponectin), while those that play a role in tumour growth and metastases are increased (like tumour necrosis factor TNF).
How are cancer and diet connected?
In South Africa, the urban diet has led to an increase in diet-induced obesity and hence an increased incidence of cancer. Our urban diet primarily consists of high glycaemic load carbohydrates, such as white bread, rice and pap, accompanied by high saturated animal fat proteins such as chicken and high-fat meat cuts. Furthermore, these foods are frequently cooked in oils which are high in omega-6 fatty acids (e.g. sunflower oil), which contributes to the high omega 6: omega 3 ratio. This has been implicated in the disease process of cancer, cardiovascular, inflammatory and auto-immune diseases.
A healthy omega 6: omega 3 ratio, associated with greatly reduced risk of disease, is regarded to be equal to or less than 4:1, whereas the ratio in the South African Western Diet is in excess of 30:1. 
How does inflammation cause cancer?
Research indicates that the factors causing obesity (e.g. diet, physical inactivity, etc.) might contribute directly to the inflammatory state.
Systemic inflammation is a pre-requisite for the development of cancer and insulin resistance may, therefore, play a pivotal role in the increased incidence of cancer in obesity, through its many interconnections with other factors which lead to obesity-related inflammation, a breeding ground for cancer development.
Systemic inflammation is not exclusive to obesity. Normal-weight individuals may experience chronic inflammation as a result of other factors, including diet and physical inactivity. As such, they are also at higher risk of developing cancer.
How are cancer and diabetes linked?
Multiple studies have shown an increased incidence and mortality of cancer in those with Type 2 diabetes, as well as an increased risk of metastases and recurrence.
Early studies found an association between diabetes and cancers of the pancreas and liver, and more recently to endometrial, breast, colorectal, bladder and kidney cancers, as well as non-Hodgkin lymphoma.
An interesting aspect to note is that the association of diabetes and cancer in these studies is independent of BMI.
Glucose is known to be a critical nutrient for proliferating cells and hyperglycaemia may play a role in combination with hyperinsulinaemia, inflammation, adipokines and altered oestrogen levels.
What are the symptoms of cancer?
CANSA has released a list of symptoms which may indicate non-specific cancer. These include:
C: Change in a wart or mole
A: A sore/ wound that doesn’t heal
U: Unusual discharge or abnormal bleeding
T: Thickening or lump
I: Indigestion or difficulty swallowing
O: On-going cough or hoarseness
N: Notable change in bowel or bladder movement
As colorectal and breast cancer are amongst the most common types of cancer and are linked directly to obesity, we will list the common symptoms.
Early breast cancer usually does not show symptoms and it is only as the tumour grows that the appearance or feeling of the breast may change.
- Common changes include:
- A lump or thickening in or near the breast or axilla
- Change in the size or shape of the breast
- Dimpling or puckering in the skin of the breast
- The nipple becoming inverted
- Abnormal discharge from the nipple
- Scaly, red or swollen skin on the breast, nipple or areola
- The skin of the breast taking on an orange-peel look or feel
Common signs and symptoms include
- A change in bowel habits, including diarrhoea or constipation or change in the consistency of the stools
- Rectal bleeding or blood in stools
- A feeling that the bowel doesn’t empty completely
- Weakness or fatigue
- Unexplained weight loss
Many people with colorectal cancer experience no symptoms in the early stages of the disease. When appearing, symptoms will likely vary, depending on the size and location of the cancer within the large bowel.
How can I decrease my risk of developing cancer?
It is estimated that approximately 1 third of all cancer cases can be prevented.
The South African Cancer Association (CANSA) advises the following lifestyle changes to reduce the risk of cancer:
- Eat fresh fruit and vegetables every day, especially apples and broccoli
- Exercise regularly
- Drink plenty of fresh, clean water daily
- Conduct regular self-examinations
- Cover up in the sun or stay in the shade
- Don’t smoke or use any tobacco products, including hubbly-bubbly
- Don’t drink more than one serving of alcohol per day
- Don’t eat processed food, junk food or food high in animal fat
- Don’t eat lots of red meat (follow a mainly plant-based and whole grain diet
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