GPs may have to correct some patients’ misunderstanding following reports in the general media suggesting that testing for high risk cancer genes was now available to everyone free of charge.
Writing in the latest issue of the MJA, Australian genetics experts say that testing for specific high- risk genetic mutations, especially BRCA1 and BRCA2 has been available to appropriate patients free of charge (but not Medicare-rebated) by genetic specialists in public clinics for over 20 years.
What’s new is that these tests now attract a Medicare rebate and you don’t have to be a genetic specialist to order them, but they are still only available to selected patients.
“Testing is appropriate when there is at least a 10% chance of identifying a gene mutation responsible for the personal or family history of cancer,” the authors of the article wrote.
There are a number of algorithms available to help clinicians calculate whether the likelihood of having one of these cancer-causing genetic mutations is at least 10%.
Usually testing is initially considered for patients who have been diagnosed with either breast or ovarian cancer, and because of their young age and/or their strong family history are considered at high possibility of having a genetic mutation that explains their condition.
The new item numbers (73295,73296 and 73297) cover testing for heritable germline mutations in seven genes including BRCA1 and BRCA2. If such a mutation is found, then at risk adult relatives will be justified in also accessing testing.
However, as the article authors point out there are limitations with this type of genetic testing. Firstly most breast and ovarian cancers occur in people without an identifiable underlying genetic variant.
“Only 5% of female breast cancers, 15% of invasive epithelial ovarian cancers and up to 14% of male breast cancers are related to BRCA1 or BRCA2 mutations, thus, most patients with breast cancer do not need, nor will they benefit from, a genetic test,” they said.
That’s not to say the absence of BRCA1 or BRCA2, or one of the other rarer high-risk mutations currently tested for, excludes the possibility that the patient has inherited a predisposition to the cancer. Families that appear to have a high prevalence of these types of cancer may indeed have an inherited genetic mutation, it is just that because of limitations of technology and knowledge it is yet to be isolated.
What’s more, the sensitivity of the current testing methods, means that a number of incidental genetic mutations may be noted, but the significance of these is as yet unknown. It is critical that when testing is requested for a relative of an affected patient, the laboratory is informed of the exact genetic variation found in the original affected patient, to ensure pathologists distinguish between the disease-causing mutation and variants of undetermined significance. The authors also suggest confining testing to only the most likely variant/s rather than requesting testing for mutations in multiple genes.
“[T]he testing of multiple genes may uncover unclassified variants, variants outside the usual clinical context, variants unrelated to the current cancer, or unexpected important variants for which the patient has not been well prepared,” they said.
They also suggest education and counselling be given to patients considering this genetic testing, and written consent obtained.
The new Medicare item numbers represent a major step forward in terms of genetic and genomic testing becoming mainstream, but, as the current incorrect media headlines demonstrate, this transition is going to require information and education. Clinicians who order these tests are likely to benefit from establishing close ties with genetic services and specialists to ensure best and appropriate practice in this ever-expanding area of medicine.
Med J Aust 2018; 209 (5): 193-196. || doi: 10.5694/mja17.01124