abstract
BACKGROUND:
Hereditary
non-polyposis colorectal cancer (HNPCC) is defined by family history,
and Lynch syndrome (LS) is defined genetically. However, universal
tumour testing is now increasingly used to screen for patients with
defective mismatch repair. This mixing of the results of family history,
tumour testing and germline testing produces multiple permutations and
combinations that can foster confusion. We wanted to clarify hereditary
colorectal cancer using the three dimensions of classification: family
history, tumour testing and germline testing.
METHODS:
Family
history (Amsterdam I or II criteria versus not Amsterdam criteria) was
used to define patients and families with HNPCC. Tumour testing and
germline testing were then performed to sub-classify patients and
families. The permutations of these classifications are applied to our
registry.
RESULTS:
There
were 234 HNPCC families: 129 had LS of which 55 were three-dimensional
Lynch (family history, tumour testing and germline testing), 66 were
two-dimensional Lynch and eight were one-dimensional Lynch. A total of
10 families had tumour Lynch (tumours with microsatellite instability or
loss of expression of a mismatch repair protein but an
Amsterdam-negative family and negative germline testing), five were
Lynch like (Amsterdam-positive family, tumours with microsatellite
instability or loss of expression of a mismatch repair protein on
immunohistochemistry but negative germline testing), 26 were familial
colorectal cancer type X and 95 were HNPCC.
CONCLUSION:
Hereditary
colorectal cancer can be confusing. Sorting families in three
dimensions can clarify the confusion and may direct further testing and,
ultimately, surveillance.
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