Characteristics of Hereditary, Familial and Sporadic Cancer Syndromes August 1, 2007Posted by ramunas in basic concepts, cancer genetics, familial cancer, hereditary cancer, sporadic cancer.
In a recently published recommendations for risk assessment and genetic counseling for hereditary breast and ovarian cancer (HBOC) in a Journal of Genetic Counseling, there is a very useful definition of 3 main type of cancer (from a geneticist point of view):
I. “Hereditary Cancer type” characteristics:
- Apparently autosomal dominant transmission of specific cancer type(s)
- Earlier age of onset of cancers than is typical
- Multiple primary cancers in an individual
- Clustering of rare cancers
- Bilateral or multifocal cancers
- First degree relatives of mutation carriers are at 50% risk to have the same mutation
- Incomplete penetrance and variable expressivity, such that obligate carriers of the family mutation may be cancer-free and the age of diagnosis of cancer among relatives will vary
- Those who do not have the familial mutation have the general population risk for cancer
II. “Familial Cancer type” chatacteristics:
- More cases of a specific type(s) of cancer within a family than statistically expected, but no specific pattern of inheritance
- Age of onset variable
- May result from chance clustering of sporadic cases
- May result from common genetic background, similar environment and/or lifestyle factors
- Does not usually exhibit classical features of hereditary cancer syndromes
III. “Sporadic Cancers type” characteristics:
- Cancers in the family are likely due to nonhereditary causes
- Typical age of onset
- Even if there is more than one case in the family, there is no particular pattern of inheritance
- Very low likelihood that genetic susceptibility testing will reveal a mutation; testing with available technology/knowledge level will likely not provide additional information about cancer risk.
This classification can help in quantifying risks to individual family members and developing a plan for cancer screening, prevention, risk reduction and psychosocial support and counseling. It also helps in the determination of whether genetic testing is appropriate for the family, and if so, which relative(s) would be the appropriate individual(s) to test. Unfortunately, the separation of families into hereditary, familial, and sporadic cancer is often not precise.
With a growing knowledge in low penetrance genes those families which were regarded as sporadic could be reclassified to familial cases. For more information please also take a look at my first post on this blog.