Breast cancer gene tests: advances and challenges

Multiple gene panel testing may be a cheaper, more accessible way to investigate the heritability of breast cancer, but it comes with ethical issues, according to a Clinical Focus published in the Medical Journal of Australia.

Twenty years after the discovery of the BRCA1 and BRCA2 genes which are responsible for 2% of breast cancer, the challenge has been to find the “missing heritability” responsible for the other 3% believed to be caused by gene mutations.

Professor Ingrid Winship, Executive Director of Research at Melbourne Health and Professor of Adult Clinical Genetics at the University of Melbourne and Royal Melbourne Hospital, and Professor Melissa Southey, from the Department of Pathology at the University of Melbourne, wrote that: “To date, tests have been conducted as single gene tests in an iterative manner, one gene at a time, at very high cost”.

“The revolution in our capacity to conduct genetic analyses in very recent years has had a profound impact on how genetic testing services can be applied,” they wrote.

“Now, a panel of multiple genes can be screened for mutations in a single test, at considerably reduced cost, via the application of massively parallel sequencing technology.”

The development of the technology has led to the discovery of more breast cancer predisposition genes and candidate genes. “Genes that are regularly included in breast cancer susceptibility gene panels that are currently available through academic or commercial testing laboratories include BRCA1, BRCA2, PALB2, PTEN, STK11, TP53, ATM, BARD1, BRIP1, CDH1, CHEK2, MRE11A, MUTYH, NBN, NF1, RAD50 and RAD51C.”

The bad news is gene panel testing also identifies “many variants of uncertain significance”, Winship and Southey wrote.

“A large grey zone exists, the so-called variants of uncertain significance, where classification is not possible, and this information cannot be used clinically,” they wrote.

“For this reason, interpretation of results, whether derived from gene panels or single gene testing, remains highly specialised and requires a team of skilled scientists, informaticians and genetic practitioners, along with research-derived evidence.”

The ability of gene panel testing to produce secondary, unanticipated, incidental findings presents challenges for clinicians, they noted.

“The consequences – that is, the clinical validity and utility of many of the genes listed – are not yet clear.”

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