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Interpret genetic test results
Interpreting genetic testing
results tool
Disclaimer:
This tool provides a basic overview of interpretation of genetic test results for hereditary cancer syndromes and is
not a substitute for clinical guidance or the consultation of an experienced genetics professional.
Individuals who have had cancer or colon polyps, when the mutation in the family
is not already known:
Positive result in an affected individual
• Disease-causing mutation was identified
• High risk of other cancers/other features (e.g., colon polyps) associated with syndrome
• Provides opportunity for relatives to be tested for the family’s specific mutation
Negative (indeterminate) in an affected individual
• Disease-causing mutation not identified
• May be true negative or false negative
■ False negative
Method of testing cannot identify causative mutation (consider referral for follow-up
testing by a genetics specialist), or
Testing did not include the gene responsible for cancer predisposition
• Still at high risk of developing additional cancers and other features (such as colon polyps)
associated with the syndrome
• Does not provide useful information for testing in relatives
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Individuals who have had cancer or colon polyps, when the mutation in the
family is known:
Positive result in an affected individual
• Disease-causing mutation identified
• High risk of developing additional cancers and other features (such as colon polyps) associated
with the syndrome
• May provide more information about risk to close relatives
Negative in an affected individual
• Disease-causing mutation not identified
• Cancer/polyps not related to known disease-causing mutation in family, i.e., sporadic
■ Note: In rare cases there may be a second inherited mutation in the family
• At increased cancer risk due to personal cancer history but no additional cancer risk
Colorectal Cancer Fact Sheets: Interpret genetic test results | 1
Interpret genetic test results
Individuals without a history of cancer or colon polyps, when the mutation in the family
is not already known:
Positive in an unaffected individual
• Disease-causing mutation identified
• At high risk of developing cancers and other features (such as colon polyps) associated with the
syndrome
• Informs testing for others in the family
Negative (indeterminate) in an unaffected individual
• Disease-causing mutation not identified
• May be true negative or false negative
■ False negative
Family may still carry a mutation, but patient may not have inherited it, or
Method of testing used cannot identify existing mutation, or
Testing did not include the gene responsible for cancer predisposition in family
• Risk is still based on personal/family history
■ Screen using appropriate guidelines
• Does not provide useful information for testing in relatives
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Individuals without a history of cancer or colon polyps, when the mutation in the family
is known:
Positive in an unaffected individual
• Disease-causing mutation identified
• High risk of developing cancers and other features (such as colon polyps) associated with the
syndrome
• May provide more information about risk to close relatives
Negative in an unaffected individual
• Disease-causing mutation not identified
• At general population risk for cancer if no other risk factors are identified
Variants of unknown significance in affected or unaffected individual:
• Change from usual genetic sequence has been identified, but the causal relationship, if any, to
cancer is uncertain (i.e., it is not clear if the change is harmful)
• Testing of relatives for variants is discouraged
• Individual should remain in contact with physician and testing lab in case new information clarifies
the meaning of test result
• Risks for cancer or cancer recurrence are based on family and medical history
11-0456:2/12:jt:Updated Feb 2012
Colorectal Cancer Fact Sheets: Interpret genetic test results | 2