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Who, why, when of genetic counselling and testing

Pearl Toh
22 Nov 2017

Indication and demand for genetic testing have increased in recent years, with tests becoming more readily available and affordable, says a leading oncologist at ESMO Asia 2017, highlighting that appreciation of ethical, social, and legal implications of testing and proper test interpretation are important for optimal patient management.

General principles: Dos and don’ts

Genetic testing is generally only offered to families with sufficient risk, usually defined as at least a 10 percent chance of carrying a genetic mutation, said Dr Lee Soo Chin from the National University Cancer Institute, Singapore. “This is not for normal- or modest-risk families.”

“Pre- and post-test counselling is essential as there are a number of ethical and social issues that you need to go through with the patients,” said Lee.

Generally, testing is also not for minors to preserve autonomy for individuals to make decisions about testing themselves, with rare exceptions whereby early intervention in childhood makes a difference, such as in the case of familial adenomatous polyposis.

When testing for hereditary cancer syndromes, the general principle is to start discovery testing in the index patient with cancer, according to Lee. Failure to identify mutation does not exclude hereditary cancer syndrome as untested or undiscovered genes may be present, she cautioned.

In the case when causative mutation is identified, predictive testing can be carried out for other family members ─ which would facilitate the classification of family members into mutation vs nonmutation carriers, with implication of different cancer risk in the respective group (high- vs normal-risk for cancer) and thus, entails different management.

Who to test?

With regards to who should be referred for genetic testing, one should consider the personal as well as the family history of cancer, Lee stated. Personal history is obvious for a physician to notice, which includes young onset cancer (with the threshold of age defined as <40 or <50 years, depending on the stringency criteria chosen), multiple primary cancers (either metachronous or synchronous), and rare cancers.

“For example, patients with breast cancer and family history of adrenocortical cancer may raise suspicion of Li-Fraumeni syndrome, [while] special features such as triple negative breast cancer with medullary features could be suggestive of BRCA [mutation],” she pointed out.  

Things to look out for when assessing family history include clustering of similar cancers, which according to Lee is often obvious, or clustering of related cancers, in which case one would need knowledge of cancer syndromes.

“Taking a detailed family history is the key to identifying familial cancers, and this should be as routine as taking a drinking and smoking history,” she emphasized.  

A good three-generation family history taking starts with close relatives of the index patient, ie, first-degree relatives (including parents, siblings, and children), followed by second- and third-degree relatives (uncles/ aunts, grandparents, nephews/nieces, and cousins) from both sides of the family.

However, Lee noted that “this is easier said than done,” highlighting a study which showed that 60 percent of at-risk cases (n=506) were not referred for formal genetic evaluation. [Clin Oncol (R Coll Radiol) 2014;26:174-175] Main reasons for nonreferral include inadequate family history assessment (45 percent) and lack of suspicion despite family history assessment (42 percent).

“Physician barriers to genetic evaluation plays a very important role which we should try to overcome in order to optimally manage these patients,” urged Lee.

Additional points to note

“Pretest counselling is crucial ─ there are ethical and social implications of genetic testing that we need to warn the patients,” said Lee, pointing out that patients might feel upset with the results and potential disruptions to family dynamics. “Equally important is the post-test counselling, whereby one needs to do proper interpretation of the test results to [ensure] optimal management of patients.”

Noting the increasing demand for genetic testing in recent years, in particular for multigene panel testing, Lee explained, “Multigene panel testing is ideal for patient with differential diagnoses as it is cheaper and faster than sequential single gene testing, but clinicians must be prepared to manage conditions due to less known genes.”  

“Family history is dynamic and continuous review and assessment is essential ... so clinicians should remind their patients for updates [over time although initial good family history has been taken],” she advised.

“For clinicians managing patients with hereditary cancer syndromes, we do have a medical legal duty to warn the patients that their family members are at risk for cancer,” reminded Lee.  

Dr Lee Soo Chin

Dr Lee Soo Chin

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Pearl Toh, 31 Dec 2019
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Pearl Toh, 04 Feb 2020
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