Cascade Testing: Extending a Genetic Result Through a Family

How It Works

The person in whom the variant was first identified is the proband. First-degree relatives (parents, siblings, children) each have a 50 percent chance of carrying a dominant pathogenic variant. Testing then radiates outward to second-degree relatives on the relevant side of the family as carriers are identified.

Cascade testing is targeted: relatives are tested only for the known familial variant, which is faster, cheaper and easier to interpret than a full panel.

Why It Matters

Relatives who test positive can access surveillance and risk-reduction options before any cancer develops. Relatives who test negative for a known familial variant usually return to population-level risk and can avoid unnecessary screening.

Because each identified carrier can lead to further relatives being tested, the population health impact of finding one variant compounds.

Practical Barriers

Uptake of cascade testing is often well below half of eligible relatives. Barriers include the proband being responsible for informing relatives, family estrangement, geographic spread, cost and insurance concerns, and low awareness.

Approaches to improve reach include direct contact of relatives by services where permitted, family-letter templates, and telephone or online counselling.

Special Situations

Testing minors is generally deferred unless childhood-onset risk is relevant, as in some TP53 or APC contexts. Predictive testing in adults is offered with counselling about the psychological and practical implications of a positive or negative result.

If a relative is tested and found not to carry the familial variant but has their own strong personal history, further evaluation may still be warranted.

Interpretation Notes

A targeted negative result in cascade testing is only meaningful because a specific pathogenic familial variant was defined first; it is not the same as a negative panel.

Cascade testing is coordinated through clinical genetics services, which manage consent, counselling and the flow of information within a family.

Key Takeaways

• ·Cascade testing offers targeted testing for a known familial variant to at-risk relatives.
• ·Carriers gain access to surveillance; true negatives can step down screening.
• ·Uptake is often low because probands must usually inform relatives themselves.
• ·A cascade negative is meaningful only against a defined familial variant.