4.1 Introduction

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Hereditary vs. Familial Cancer

 

Although approximately 70 - 75% of all cancers arise sporadically (i.e. are non-hereditary and non-germline), a significant number of cancers have been linked to inheritance of alleles known to dramatically increase an individuals risk of cancer (1). This predisposition greatly increases the chance of developing malignancies. The BC Cancer Agency makes the distinction between “familial” and “hereditary” cancer based on the the degree to which a specific mutation is linked to development of a specific cancer . Up to 10% of cancers are truly hereditary, and are known to be caused by certain mutations. An estimated 20-25% of cancers are familial, indicating a weaker, but still significant genetic basis (1).

The presence of certain hallmarks leads to classification of a cancer as "hereditary.” When a specific type of cancer shows up in two or more direct relatives on the same side of the family, this is usually indicative of an inherited component to the cancer. Presence of the cancer in multiple generations is also a characteristic of hereditary cancer (1). Other signs include the presence of multiple primary tumours in an individual, the presence of bilateral tumours (tumours in paired organs), or the occurrence of an extremely rare tumour such as ocular melanoma (2). It is important to note that hereditary cancers are typically characterized by an early age of diagnosis (<40 years of age) in at least one individual.

Familial cancers share many of the same characteristics as hereditary cancer, except to a lesser degree. Cancers in these individuals are typically diagnosed at an older age than their hereditary counterparts. On pedigrees, a specific type of cancer may skip generations, but it will show up more often than expected if it were sporadic. The mutations involved in familial cancer are not thought to be in the “major” tumour suppressor genes. As a result, environmental factors play a larger role in familial cancer than they do in true hereditary cancer.

 

Risk Management

 

Genetic counseling services are available for individuals deemed to be at high risk of carrying mutations that result in heritable cancer (these individuals come from families that have the chararcteristics of hereditary cancer as outlined above). This process helps at-risk individuals to understand their situation, decide whether or not they would like to proceed with genetic testing, and implement screening plans. Testing usually begins with the affected individual, and proceeds to look at their parents and children, if applicable (1).

 

 

Future Directions

 

Currently, research is being conducted to identify novel gene mutations and variants that lead to the development and progression of cancer. The completed Human Genome Project and the ongoing Cancer Genome Project use sequencing and high-throughput analysis to locate these genetic changes and will hopefully aid in our understanding and treatment of cancer.


Modes of Inheritance, Hereditary Cancer Syndrome, Genetic Counseling, and examples of hereditary dominant and recessive cancers are discussed in the sections that follow.

 

References

1. BC Cancer Agency (2013). Cancer Genetic Counseling. MEDG 421 lecture on 17.01.2013.

2. National Cancer Institute (2013). Cancer Genetics Risk Assessment and Counseling. Accessed 02.03.2013 from http://www.cancer.gov/cancertopics/pdq/genetics/risk-assessment-and-counseling/HealthProfessional/page1

3. Weinberg, R. (2007). The Biology of Cancer (New York: Garland Science, Taylor & Francis Group, LLC)