The Variant of Uncertain Significance in a Family With No Living Affected Relative
A 34-year-old woman (proband) with early-onset breast cancer at 31 and no other affected relatives undergoes multi-gene panel testing. The laboratory reports a missense variant in a moderate-risk gene, classified as a Variant of Uncertain Significance (VUS). Her parents are both deceased; she has one healthy sister and two young children. The laboratory notes the variant has a population frequency of 0.0008 and in silico tools predict damaging, but there is no functional data and no segregation data. The proband asks whether her sister should be tested and whether her children are at risk. She is anxious and wants 'something done.' Her oncologist has asked whether the result changes surgical planning for contralateral risk.
1. How would you explain the VUS to the proband, and what is your recommendation regarding testing her sister and children?
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Key reasoning:
Define the VUS clearly: A VUS is a change whose link to disease is not established. It is not the same as a negative result and not a positive result. Explain that reclassification can occur in either direction over time.
Do not use the VUS for predictive testing of relatives. Because the variant's pathogenicity is unproven, testing the sister or children would produce a result that cannot be acted upon and could cause harm (over-treatment, anxiety, insurance concerns). Family testing is only meaningful once the variant is reclassified as pathogenic.
Avoid the 'reverse cascade' trap: Some clinicians test relatives to gather segregation data. This is a research activity, not clinical care, and requires consent and ethics oversight. Do not frame it as clinical testing.
Offer surveillance based on personal and family history, not on the VUS. Her own early-onset breast cancer drives management regardless.
Document a plan to recontact if the variant is reclassified, and tell her this explicitly. Ask the lab about their reclassification policy.
Address the oncologist's question honestly: A VUS should not be used to justify contralateral prophylactic mastectomy. Surgical decisions should rest on established risk factors, not the VUS.
2. The sister asks to be tested 'just to know.' How do you counsel her, and what ethical principles are in tension?
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Counsel the sister that:
- A test result for a VUS is uninterpretable; a 'positive' result would not mean she has increased risk, and a 'negative' result would not mean she is protected.
- Testing could create a false sense of security or unnecessary anxiety.
- If the variant is later reclassified, testing can be offered then, using stored DNA if available.
Ethical tensions:
- Autonomy (she wants information) versus non-maleficence (the information is not actionable and may harm).
- Beneficence: offering surveillance based on family history serves her better than a VUS result.
- Resource stewardship: testing for an uninterpretable variant consumes resources without benefit.
Resolution: Respect autonomy by explaining why the test is not informative, offer genetic counselling and family-history-based risk assessment, and leave the door open. Do not simply refuse; explain the reasoning. Document the discussion.