80% of cancers preventable

A recent American Cancer Society report estimates that cancer claims 20 000 lives worldwide every day. The report also indicates that many of these deaths are preventable.

Apart from making the necessary lifestyle changes, new treatments remain a key part of the battle against cancer. One of the key new areas of research is genetics. With our understanding of genes and their link to cancer expanding rapidly, approaches to the prevention, surveillance and treatment of cancer are changing significantly.

80% of cancers preventable
Approximately 80% of all cancers are potentially preventable (this statistic was given a boost by the vaccine that is now available against HPV and, thereby, cervical cancer - ed). It has been shown that the best ways to avoid cancer are similar to those needed to prevent obesity and heart disease.

Smoking, unhealthy diets, alcohol abuse, and obesity have all been linked to an increased risk of cancer.

However, as the genetic puzzle keeps unfolding and the links between specific genes and related risks become clearer, the possibility of changing your diet to cut your cancer risk is becoming a reality.

Genetic testing is not only used as a risk-determining tool, it is also increasingly used for cancer diagnosis, for prognosis to determine the clinical behaviour of a tumour, and to predict the potential outcome of therapy and assist with the selection of optimal treatment.

How genetic tests are helping
A practical example of how genetic testing can assist in a cancer diagnosis situation is a new genetic test for breast cancer prognostication that has recently become available in South Africa.

Termed the MammaPrint, this specific test assesses the activity of 70 genes in a tumour to determine whether the person has a low or high risk that the cancer may spread to other parts of the body.

Approximately 60% of breast cancer patients are classified as high risk when the genetic test is used compared with 85% based on clinical features only.

Patients with a poor prognosis profile have a one in two chance of developing metastases and dying within 10 years. These patients therefore need aggressive chemotherapy to improve their survival, even in the case of small tumours and no lymph node infiltration.

By contrast, those who have a good prognosis profile have a four in 100 chance of developing metastases and dying and therefore do not require aggressive therapy.

One in three spared chemo
What this means is that one in three patients will be spared chemotherapy. "This is a major relief to patients as chemotherapy is the most dreaded part of breast cancer therapy", according to Professor Justus Apffelstaedt, head of the Breast Clinic at Tygerberg Hospital.

"A startling experience is that while a large number of patients are saved from having to undergo chemotherapy, there are a small number of patients who, with conventional prognostication, are thought not to need chemotherapy, but whose tumours then have a poor prognosis profile. These patients need chemotherapy despite having very small tumours and no lymph nodes involved. It is particularly important for these patients to be identified with the help of genetic screening to improve their chances of survival," he said.

It has been suggested that genetic counselling should be offered to all cancer patients and their at-risk family members.

Benefits and limitations
Affected patients need to understand the potential benefits as well as the limitations of genetic test options, ranging from diagnostic to predictive tests that could be linked to particular risk reduction interventions.

According to Dr Maritha Kotze of the University of Stellenbosch: "Genetic testing allows people to derive personal meaning and empowerment from the information communicated to them during counselling sessions and to make informed decisions based on their results."

Ultimately, comprehensive cancer genetic testing offered as part of routine clinical practice would translate into cancer prevention at the population level, she said.

Cancer facts

  • Three in 5 people are predicted to develop cancer during their lifetime and 1 in 5 will die from the disease.
  • Approximately 5 - 10% of cancers are inherited in families.
  • Most sporadic cancers are caused by an interaction between genetic factors and environmental risk factors.
  • Diet-related factors account for approximately 30% of cancers in developed countries.
  • Obesity increases the risk of cancers of the breast, colorectum, oesophagus, endometrium and kidney – the risk of breast cancer is increased by approximately 50% in postmenopausal women.
  • Alcohol causes cancers of the oral cavity, pharynx, larynx, oesophagus, liver and increases the risk of breast cancer.
  • Diet is second to tobacco smoking as a potentially preventable cause of cancer.

- (Dr Maritha Kotze, Department of Pathology, University of Stellenbosch and Professor Justus Apffelstaedt, Associate Professor, University of Stellenbosh and Head of the Breast Clinic, Tygerberg Hospital)

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