Genetic testing is a complex topic. Your Genetic Counsellor will have spoken to you about genetic testing and how genetic testing information is considered in your family. The section below provides some background information about common types of genetic testing and genetic testing results.
FAMILIAL BREAST CANCER AND GENETIC TESTING
Many women have a family history of breast cancer as it is very common in the general population, affecting 1 in 8 women. Some women have a family history (a group of close relatives have been affected by breast cancer) indicating there may be an underlying inherited genetic cause. This is referred to as a ‘familial cluster’ (see Figure 1 below).
Some of these familial clusters will be explained
by (alterations) mutations in the BRCA1/2 genes. Some will be explained by other rare high risk genes, moderate risk genes and/or common genomic variants (low risk genes). Currently, there is no genetic testing available for the moderate risk breast cancer genes and common genomic variants as researchers are still trying to understand how much the genes contribute to the risk how best to manage it.
Therefore, despite having made significant discoveries into genes which explain familial breast cancer, 50% of families with familial breast cancer remain unexplained by current genetic knowledge.
Familial Cancer Clinics can predict which families are more likely to have a high risk single gene versus those that may be explained for other reasons.
The most common single high risk genes are BRCA1 and BRCA2. Family history and pathology (type) of breast cancer are entered into a computer algorithm program generating a score that determines the likelihood of a BRCA1 and BRCA2 gene mutation.
The national guidelines (eviQ) followed by Familial Cancer Clinics in Australia to determine when publicly funded genetic testing is offered recommend offering genetic testing for BRCA1/2 where there is a >10% chance a BRCA1 or BRCA2 gene mutation and where there is someone alive, who has had breast cancer and willing to be tested (EVIQ). As this threshold of 10% is set low, most families who are offered publicly funded genetic testing will not have a BRCA1 or BRCA2 mutation identified.
Research is continuing and other gene mutations related to breast and/or ovarian cancer that have been discovered more recently are STK11, PTEN, CDH1, PALB2 and TP53. Familial Cancer Clinics can provide further information and testing options for these gene mutations.