Cancer Risk Assessment for the Primary Care Physician

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Family history assessment

Family history is a known risk factor for a multitude of chronic diseases, including cardiovascular disease, diabetes, and cancer; thus, obtaining a family history of medical illness is a recognized and important component of primary care assessment. From the standpoint of cancer risk assessment, a thorough family history should include all of the following components:

  • Ethnic background of each grandparent.

  • Information about maternal and paternal relatives.

  • Information on at least first-degree

Hereditary breast and ovarian cancer

It is estimated that 5% to 10% of breast cancers occur in women with an inherited susceptibility to cancer.13 Most of these are women with hereditary breast and ovarian cancer syndrome (HBOC), which is explained by deleterious mutations in the BRCA1 and BRCA2 genes, although several less common genetic disorders, such as Li-Fraumeni syndrome, Cowden syndrome, and Peutz-Jeghers syndrome also include a predisposition to breast cancer.12 These syndromes exhibit autosomal dominant inheritance.

Hereditary colon cancer

Approximately 20% of individuals diagnosed with colon cancer have a strong family history (2 or more first- or second-degree relatives), and about 3% to 5% of colon cancers occur in the context of genetically defined high-risk syndromes.27 The two most common of these are hereditary nonpolyposis colorectal cancer (HNPCC or Lynch syndrome) and familial adenomatous polyposis (FAP), which are inherited in an autosomal dominant fashion.

HNPCC-associated cancers result from mutations in one of

Familial prostate cancer

Familial clustering of prostate cancer has been well described, but to date no specific high-penetrance susceptibility genes have been identified, and thus clinical genetic testing is not currently available. Several candidate genetic loci have been identified in linkage analyses and, more recently, in genome-wide association studies.32 However, the preponderance of data suggests that the genetic basis of prostate cancer is incredibly complex, and this is an area of active research.

Family

Familial melanoma

It is estimated that 5% to 7% of melanoma patients are from genetically at-risk families. Familial melanoma is generally defined by the presence of 3 or more affected blood relatives in families located in regions of intense sun exposure or 2 or more affected family members in areas with less intense sun exposure. Individuals with an inherited predisposition to melanoma are prone to early-onset disease (mean age at diagnosis is 34 years) and tend to develop multiple primary melanomas.36

Cancer risk assessment models

Statistical models for cancer risk prediction fall into 2 broad categories: those that are used to predict the probability of being diagnosed with a particular cancer, and those that predict the likelihood of carrying a gene mutation that predisposes to a particular cancer or set of cancers. Several commonly used risk assessment models for common cancers are described in the following sections.

Modifiable cancer risk factors

It is believed that cancer may be a fundamentally preventable disease; as many as 90% to 95% of all cancers are attributed to potentially modifiable behavioral and environmental risk factors.53 Most important among these factors are tobacco, alcohol consumption, and obesity. Thus, by assessing and influencing lifestyle factors during primary care visits, the physician may have a considerable effect on cancer incidence and patient outcomes.

Summary

Primary care physicians are uniquely situated to identify individuals at increased genetic or environmental risk of cancer. The early identification of a suspected heritable cancer syndrome can lead to additional evaluation and to interventions that can substantially decrease cancer risk. Web-based tools for collecting and summarizing family history information and for predicting individual risks for certain cancers and familial syndromes are easily accessible and are available for use by the

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