‘Personality gene’ testing for targeted breast cancer treatment
Posted on 26 May 2017
Traditionally, cancer treatment has been determined by the external features of the cancer, such as the size and appearance of tumours. But tests that analyse what can be called the ‘personality’ of the cancer are now changing the very nature and effectiveness of cancer treatment.
Genetic testing versus genetic typing
Only a small group of patients have faulty genes that can be identified in a blood test, such as BRCA genes (BRCA1 is a tumour suppressor gene found in all humans, and its protein is responsible for repairing DNA). If these genes are abnormal, there is a high risk of developing breast cancer when accompanied by certain factors.
‘These genes are heavily dependent on environmental factors, which may include prolonged use of oral contraceptives, teenage drinking, smoking, obesity and delayed pregnancy. (Earlier pregnancy matures the breast cells, making them less susceptible to cancer),’ says Dr Ettienne Myburgh, an oncology surgeon at Panorama Mediclinic. The latest research also shows that over 80 faulty genes could contribute to the formation of a certain cancer, making it difficult to test for specific genes.
Genetic typing of cancers is different from analysing the patient’s genes that might cause a risk for developing breast cancer. Rather, it focuses on looking at the genetic profile of the cancer. Genetic typing reduces the possibility of overtreatment (treating cancer too aggressively) because it enables oncologists to offer the patient a personalised treatment approach to their specific tumour.
Past treatment protocols
‘Previously, we’ve looked at external features to try to predict what the personality of a cancer is, but we haven’t been very good with that,’ says Dr Myburgh. ‘We used to say if cancers get to a certain size – generally 1.5 to 2cm – or if lymph nodes are involved, or with grade three cancers which might grow faster, those patients should all have chemo.’
But, he adds, in reality, if 100 women with early breast cancer were all given chemotherapy, only about 15% of them would benefit from it.
Personality tests for treating cancer
‘We now know that each cancer has its own set of genes that will determine how the cancer will behave – in other words, the cancer’s personality,’ elaborates Dr Myburgh. With personalised medicine, he explains that they’re not looking at the external features of the cancer, but at the cancer’s genetic subtype or ‘personality’. ‘Essentially, we look at the genes inside the cancer to tell us whether that cancer is aggressive or not.’
There are four genetic sub-types of breast cancer – luminal A, luminal B, basal, and HER2-enriched – that do not necessarily correlate with what can be seen under the microscope. The test for these subtypes consists of MammaPrint and BluePrint assessments and work by analysing the genes within the cancer itself. MammaPrint determines the risk of the cancer spreading and BluePrint will indicate the molecular sub-type of the cancer.
- Luminal A breast cancers are very oestrogen sensitive but they are not chemotherapy sensitive, so chemotherapy would not add any benefit.
- Luminal B breast cancers are still oestrogen sensitive, but will benefit from chemotherapy in addition to anti-oestrogen treatment.
- Basal-like breast cancers do not respond to oestrogen at all and are solely treated with chemotherapy.
- HER2-enriched breast cancers will require Herceptin and chemotherapy, but will generally not respond to anti-oestrogen alone.
With standard pathology it is impossible to accurately determine the exact cancer subtype but using the BluePrint test, the most appropriate treatment can be planned based on the molecular subtyping, which reflects the personality of the cancer. Once the cancer has been diagnosed, oncologists will look at historic patients falling within a subtype and how they responded to certain treatments. This effectively leverages big data for more targeted cancer treatments.