THE BREAST DEFENCE

The fact that there isn't any cancer in your family doesn't mean you can't get breast cancer. Only 10% of cases are linked to inherited genetic factors – the other 90% occur without any clear warning. That's why regular screenings and self-examination are vital.

- Kathy Malherbe

When we talk about 'genetics' in breast cancer, we need to distinguish between two distinct factors, says clinical and radiation oncologist Dr Lizanne Langenhoven. The first is a woman's inherited genetic makeup, which influences her likelihood of developing breast cancer. The second comes into play after a diagnosis; the genetic characteristics of the cancer itself need to be considered, regardless of whether the person carries a known breast cancer gene. Tumour-specific traits determine the most effective course of treatment.

INHERITING THE GENE

Each parent contributes half of our genetic makeup when we are conceived. Think of it as receiving a recipe book from each parent, with the necessary information to create all the parts of a living human being. Some families have an error in the recipe for the so-called ‘tumour-suppressor genes’ — a group of genes that detect DNA damage and repair or destroy these damaged cells, thereby preventing the formation of cancer.

So how does it work?

Carriers of certain genetic mutations are born with only one functional copy — rather than the usual two — of the genes that help suppress cancer, one from each parent. Over time, if this single working copy is damaged by factors such as ageing, lifestyle or environmental exposure, there is no backup to keep abnormal cell growth in check, increasing the risk of cancer. For women with one of these mutations, the lifetime risk of developing breast cancer is between 30% and 80%, as opposed to 12% for those without a mutation.

Several genes can increase the risk of breast cancer, but you're probably most familiar with BRCA1 and BRCA2. Most of us likely heard of these genes for the first time when Angelina Jolie revealed that she had inherited a BRCA mutation. To reduce her risk of developing breast and ovarian cancer, she chose to have a bilateral mastectomy, followed by the removal of her ovaries.