General Information
Family History as a Risk Factor for Breast Cancer
Family History as a Risk Factor for Ovarian Cancer
Autosomal Dominant Inheritance of Breast/Ovarian Cancer Predisposition
Difficulties in Identifying a Family History of Breast and Ovarian Cancer Risk
Other Risk Factors for Breast Cancer
        Age
        Reproductive and menstrual history
        Oral contraceptives
        Radiation exposure
        Alcohol intake
        Benign breast disease and mammographic density
        Other factors
Other Risk Factors for Ovarian Cancer
        Age
        Reproductive history
        Surgical history
        Oral contraceptives
Models for Prediction of Breast Cancer Risk

General Information

 [Note: Many of the medical and scientific terms used in this summary are found in the NCI Dictionary of Genetics Terms. When a linked term is clicked, the definition will appear in a separate window.]

Among women, breast cancer is the most commonly diagnosed cancer after nonmelanoma skin cancer, and is the second leading cause of cancer deaths after lung cancer. In 2008, an estimated 182,460 new cases will be diagnosed, and 40,480 deaths from breast cancer will occur.[1] The incidence of breast cancer, particularly for estrogen receptor-positive cancers occurring after age 50 years, has declined at a faster rate since 2003; this may be temporally related to a decrease in hormone replacement therapy following early reports from the Women’s Health Initiative.[2] Ovarian cancer is the eighth most common cancer, with an estimated 21,650 new cases in 2008, but is the fifth most deadly, with an estimated 15,520 deaths in 2008.[1] (Refer to the PDQ summary on Breast Cancer Treatment and Ovarian Epithelial Cancer Treatment for more information on breast cancer and ovarian cancer rates, diagnosis, and management.)

A possible genetic contribution to both breast and ovarian cancer risk is indicated by the increased incidence of these cancers among women with a family history (see the Family History as a Risk Factor for Breast Cancer and the Family History as a Risk Factor for Ovarian Cancer sections below), and by the observation of rare families in which multiple family members are affected with breast and/or ovarian cancer, in a pattern compatible with autosomal dominant inheritance of cancer susceptibility. Formal studies of families (linkage analysis) have subsequently proven the existence of autosomal dominant predispositions to breast and ovarian cancer and have led to the identification of several highly penetrant genes as the cause of inherited cancer risk in many cancer-prone families. (Refer to the PDQ summary Cancer Genetics Overview for more information on linkage analysis.) Mutations in these genes are rare in the general population and are estimated to account for no more than 5% to 10% of breast and ovarian cancer cases overall. It is likely that other genetic factors contribute to the etiology of some of these cancers.

In cross-sectional studies of adult populations, 5% to 10% of women have a mother or sister with breast cancer, and about twice as many have either a first-degree relative or a second-degree relative with breast cancer.[3-6] The risk conferred by a family history of breast cancer has been assessed in both case-control and cohort studies, using volunteer and population-based samples, with generally consistent results.[7] In a pooled analysis of 38 studies, the relative risk (RR) of breast cancer conferred by a first-degree relative with breast cancer was 2.1 (95% confidence interval [CI], 2.0-2.2).[7] Risk increases with the number of affected relatives and age at diagnosis.[4,5,7] Refer to the Penetrance of Mutations section for a discussion of familial risk for women from families with BRCA1/2 mutations who themselves test negative for the family mutation.

Although reproductive, demographic, and lifestyle factors affect risk of ovarian cancer, the single greatest ovarian cancer risk factor is a family history of the disease. A large meta-analysis of 15 published studies estimated an odds ratio (OR) of 3.1 for the risk of ovarian cancer associated with at least one first-degree relative with ovarian cancer.[8]

Autosomal dominant inheritance of breast/ovarian cancer is characterized by transmission of cancer predisposition from generation to generation, through either the mother’s or the father’s side of the family, with the following characteristics:

• Inheritance risk of 50%. When a parent carries an autosomal dominant genetic predisposition, each child has a 50:50 chance of inheriting the predisposition. Although the risk of inheriting the predisposition is 50%, not everyone with the predisposition will develop cancer because of incomplete penetrance and/or gender-restricted or gender-related expression.



• Both males and females can inherit and transmit an autosomal dominant cancer predisposition. A male who inherits a cancer predisposition and shows no evidence of it can still pass the altered gene on to his sons and daughters.

Breast and ovarian cancer are components of several autosomal dominant cancer syndromes. The syndromes most strongly associated with both cancers are BRCA1 or BRCA2 mutation syndromes. Breast cancer is also a common feature of Li-Fraumeni syndrome due to TP53 mutations; of Cowden syndrome due to PTEN mutations; and with mutations in CHEK2 .[9] Other genetic syndromes that may include breast cancer as an associated feature include heterozygous carriers of the ataxia telangiectasia (AT) gene and Peutz-Jeghers syndrome. Ovarian cancer has also been associated with Lynch syndrome, basal cell nevus (Gorlin) syndrome (OMIM), and multiple endocrine neoplasia type 1 (MEN1) (OMIM).[9] Mutations in each of these genes produce different clinical phenotypes of characteristic malignancies and, in some instances, associated nonmalignant abnormalities.

The family characteristics that suggest hereditary breast and ovarian cancer predisposition include the following:

• Cancers typically occur at an earlier age than in sporadic cases (defined as cases not associated with genetic risk).



• Two or more primary cancers in a single individual. These could be multiple primary cancers of the same type (e.g., bilateral breast cancer) or primary cancer of different types (e.g., breast and ovarian cancer in the same individual).



• Cases of male breast cancer.



• Possible increased risk of other selected cancers and benign features for males and females. (Refer to the Major Genes section of this summary for more information.)

There are no pathognomonic features distinguishing breast and ovarian cancers occurring in BRCA1 or BRCA2 mutation carriers with those occurring in noncarriers. Breast cancers occurring in BRCA1 mutation carriers are more likely to be estrogen receptor (ER)-negative, progesterone receptor (PR)-negative, and HER2/neu receptor-negative and have a basal phenotype. BRCA1-associated ovarian cancers are unlikely to be of mucinous or borderline histopathology. [Refer to the Pathology/Prognosis of Breast Cancer and Pathology/Prognosis of Ovarian Cancer sections for more information.]

When using family history to assess risk, the accuracy and completeness of family history data must be taken into account. A reported family history may be erroneous, or a person may be unaware of relatives affected with cancer. In addition, small family sizes and premature deaths may limit the information obtained from a family history. Breast or ovarian cancer on the paternal side of the family usually involves more distant relatives than on the maternal side and thus may be more difficult to obtain. When comparing self-reported information with independently verified cases, the sensitivity of a history of breast cancer is relatively high, at 83% to 97%, but lower for ovarian cancer, at 60%.[10,11]

Other risk factors for breast cancer include age, reproductive and menstrual history, hormone therapy, radiation exposure, mammographic breast density, alcohol intake, physical activity, anthropometric variables, and a history of benign breast disease. (Refer to the PDQ summary on Prevention of Breast Cancer for more information.) These factors are considered in more detail in numerous reviews,[12,13] including among BRCA1/BRCA2 mutation carriers.[14] Brief summaries are given below, highlighting, where possible, the effect of these risk factors in women who are genetically susceptible to breast cancer. (More information about their effects in BRCA1/BRCA2 mutation carriers can be found in the section on Interventions later in this document.)

Cumulative risk of breast cancer increases with age, with most breast cancers occurring after age 50 years.[15] In women with a genetic susceptibility, breast cancer, and to a lesser degree, ovarian cancer, tends to occur at an earlier age than in sporadic cases.

Breast cancer risk increases with early menarche and late menopause, and is reduced by early first full-term pregnancy. Although results have been complex and may be gene dependent, several studies have suggested that the influence of these factors on risk in BRCA1/BRCA2 mutation carriers appear to be similar to noncarriers.[14,16]

Oral contraceptives may produce a slight increase in breast cancer risk among long-term users, but this appears to be a short-term effect. In a meta-analysis of data from 54 studies, the risk of breast cancer associated with oral contraceptive use did not vary according to a family history of breast cancer.[17]

Oral contraceptives are sometimes recommended for ovarian cancer prevention in BRCA1 and BRCA2 mutation carriers, but studies of their effect on breast cancer risk have been inconsistent.[18-20]

Data exist from both observational and randomized clinical trials regarding the association between postmenopausal hormone replacement therapy (HRT) and breast cancer. A meta-analysis of data from 51 observational studies indicated a RR of breast cancer of 1.35 (95% CI, 1.21–1.49) for women who had used HRT for 5 or more years after menopause.[21] The Women's Health Initiative (WHI), a randomized controlled trial of about 160,000 postmenopausal women, investigated the risks and benefits of HRT. The estrogen-plus-progestin arm of the study, which randomized more than 16,000 women to receive combined HRT or placebo, was halted early because health risks exceeded benefits.[22,23] Adverse outcomes prompting closure included significant increase in both total (245 vs. 185 cases) and invasive (199 vs. 150 cases) breast cancers (RR = 1.24; 95% CI, 1.02–1.5, P <.001) and increased risks of coronary heart disease, stroke, and pulmonary embolism. Similar findings were seen in the estrogen-progestin arm of the prospective observational Million Women’s Study in the United Kingdom.[24] The risk of breast cancer was not elevated, however, in women randomly assigned to estrogen-only versus placebo in the WHI study (RR = 0.77; 95% CI, 0.59–1.01). Eligibility for the estrogen-only arm of this study required hysterectomy, and 40% of these patients also had undergone oophorectomy, which potentially could have impacted breast cancer risk.[25]

The association between HRT and breast cancer risk among women with a family history of breast cancer has not been consistent; some studies suggest risk is particularly elevated among women with a family history, while others have not found evidence for an interaction between these factors.[26-30,21] The increased risk of breast cancer associated with HRT use in the large meta-analysis did not differ significantly between subjects with and without a family history. The WHI study has not reported analyses stratified on breast cancer family history, and subjects have not been systematically tested for BRCA1/2 mutations.[23] Short-term use of hormones for treatment of menopausal symptoms appears to confer little or no breast cancer risk.[21,31] The effect of HRT on breast cancer risk among carriers of BRCA1 or BRCA2 mutations has been studied only in the context of bilateral risk-reducing oophorectomy, in which short-term replacement does not appear to reduce the protective effect of oophorectomy on breast cancer risk.[32]

Observations in survivors of the atomic bombings of Hiroshima and Nagasaki and in women who have received therapeutic radiation treatments to the chest and upper body document increased breast cancer risk as a result of radiation exposure. The significance of this risk factor in women with a genetic susceptibility to breast cancer is unclear.

Preliminary data suggest that increased sensitivity to radiation could be a cause of cancer susceptibility in carriers of BRCA1 and BRCA2 mutations,[33-36] and in association with germline ATM and TP53 mutations.[37,38] Since BRCA1/2 mutation carriers are heterozygotes, however, radiation sensitivity might occur only after a somatic mutation has damaged the normal copy of the gene.

The possibility that genetic susceptibility to breast cancer occurs via a mechanism of radiation sensitivity raises questions about radiation exposure. It is possible that diagnostic radiation exposure, including mammography, poses more risk in genetically susceptible women than in women of average risk. Therapeutic radiation could also pose carcinogenic risk. A cohort study of BRCA1 and BRCA2 mutation carriers treated with breast-conserving therapy, however, showed no evidence of increased radiation sensitivity or sequelae in the breast, lung, or bone marrow of mutation carriers.[39] Conversely, radiation sensitivity could make tumors in women with genetic susceptibility to breast cancer more responsive to radiation treatment. Studies examining the impact of mammography and chest x-ray exposure in BRCA1 and BRCA2 mutation carriers have had conflicting results.[40,41] (Refer to text on Radiation in the Interventions section of this summary for more information.)

The risk of breast cancer increases by approximately 10% for each 10g of daily alcohol intake (approximately 1 drink or less) in the general population.[42,43] One study of BRCA1/BRCA2 mutation carriers found no increased risk associated with alcohol consumption.[44]

Weight gain and being overweight are commonly recognized risk factors for breast cancer. In general, overweight women are most commonly observed to be at increased risk of postmenopausal breast cancer and at reduced risk of premenopausal breast cancer. Sedentary lifestyle may also be a risk factor.[45] These factors have not been systematically evaluated in women with a positive family history of breast cancer or in carriers of cancer-predisposing mutations, but one study suggested a reduced risk of cancer associated with exercise among BRCA1 and BRCA2 mutation carriers.[46]

Benign breast disease (BBD) is a risk factor for breast cancer, independent of the effects of other major risk factors for breast cancer (age, age at menarche, age at first live birth, and family history of breast cancer).[47] There may also be an association between benign breast disease and family history of breast cancer.[48]

An increased risk of breast cancer has also been demonstrated for women who have increased density of breast tissue as assessed by mammogram,[47,49,50] and breast density may have a genetic component in its etiology.[51-53]

Other risk factors, including those that are only weakly associated with breast cancer and those that have been inconsistently associated with the disease in epidemiologic studies (e.g., cigarette smoking), may be important in subgroups of women defined according to genotype. For example, some studies have suggested that certain N-acetyl transferase alleles may influence female smokers’ risk of developing breast cancer.[54] One study [55] found a reduced risk of breast cancer among BRCA1/2 mutation carriers who smoked, but an expanded follow-up study failed to find an association.[56]

Factors that increase risk for ovarian cancer include increasing age and nulliparity, while those that decrease risk include surgical history and oral contraceptives.[57,58] (Refer to the PDQ summary on Prevention of Ovarian Cancer for more information.) Relatively few studies have addressed the effect of these risk factors in women who are genetically susceptible to ovarian cancer. (Refer to the Risk Modification section for more information.)

Ovarian cancer incidence rises in a linear fashion from age 30 years to age 50 years and continues to increase, though at a slower rate, thereafter. Before age 30 years, the risk of developing epithelial ovarian cancer is remote; even in hereditary cancer families.[59]

Nulliparity is consistently associated with an increased risk of ovarian cancer, including among BRCA1/BRCA2 mutation carriers.[60] Risk may also be increased among women who have used fertility drugs, especially those who remain nulligravid.[57,61] Evidence is growing that the use of menopausal HRT is associated with an increased risk of ovarian cancer, particularly in long-time users and users of sequential estrogen-progesterone schedules.[62-65]

Bilateral tubal ligation and hysterectomy are associated with reduced ovarian cancer risk,[57,66,67] including in BRCA1/BRCA2 mutation carriers.[68] Ovarian cancer risk is reduced more than 90% in women with documented BRCA1 or BRCA2 mutations who chose risk-reducing salpingo-oophorectomy (RRSO). In this same population, prophylactic removal of the ovaries also resulted in a nearly 50% reduction in the risk of subsequent breast cancer.[69,70] For further information on these studies refer to the Risk-Reducing Salpingo-Oophorectomy section of this summary.

Use of oral contraceptives for 4 or more years is associated with an approximately 50% reduction in ovarian cancer risk in the general population.[57,58] A majority of, but not all, studies also support oral contraceptives being protective among BRCA1/ BRCA2 mutation carriers.[60,71-74]

Models to predict an individual’s lifetime risk for developing breast cancer are available. In addition, models exist to predict an individual’s likelihood of having a BRCA1 or BRCA2 mutation. For further information on these models refer to the Models for Prediction of the Likelihood of a BRCA1 or BRCA2 Mutation section of this summary. Not all models can be appropriately applied for all patients. Each model is appropriate only when the patient’s characteristics and family history are similar to the study population on which the model was based. The table, Characteristics of the Gail and Claus Models, summarizes the salient aspects of the risk assessment models and is designed to aid in choosing the one that best applies to a particular individual.

Two models for predicting breast cancer risk, the Claus model [75,76] and the Gail model,[77] are widely used in research studies and clinical counseling. Both have limitations, and the risk estimates derived from the two models may differ for an individual patient. These models, however, represent the best methods currently available for individual risk assessment.

It is important to note that these models will significantly underestimate breast cancer risk for women in families with hereditary breast cancer susceptibility syndromes. In those cases, Mendelian risks would apply. A 3-generation cancer family history is taken before applying any model. (Refer to the PDQ summary on Cancer Genetics Risk Assessment and Counseling for more information on Taking a Family History.) Generally, the Claus or Gail models should not be the sole model used for families with one of the following characteristics:

• Three individuals with breast or ovarian cancer (especially when one or more breast cancers are diagnosed before age 50 years).
• A woman who has both breast and ovarian cancer.
• Ashkenazi Jewish ancestry with at least one case of breast or ovarian cancer (as these families are more likely to have a hereditary cancer susceptibility syndrome).

The Gail model has been found to be reasonably accurate at predicting breast cancer risk in large groups of white women who undergo annual screening mammography.[81-85] While the model is reliable in predicting the number of breast cancer cases expected in a group of women from the same age-risk strata, it is less reliable in predicting risk for individual patients. Risk can be overestimated in:

• Nonadherent women (i.e., does not adhere to screening recommendations).[81,82]
• Women in the highest risk strata.[84]

Risk could be underestimated in the lowest risk strata.[84] Earlier studies [81,82] suggested risk was overpredicted in younger women and underpredicted in older women. More recent studies [83,84] using the modified Gail model (which is currently used) found it performed well in all age groups. Further studies are needed to establish the validity of the Gail model in minority populations.[85]

A study of 491 women aged 18 to 74 years with a family history of breast cancer compared the most recent Gail model to the Claus model in predicting breast cancer risk.[86] The two models were positively correlated (r = .55). The Gail model estimates were higher than the Claus model estimates for most participants. Presentation and discussion of both the Gail and Claus models risk estimates may be useful in the counseling setting.

The Gail model is the basis for the Breast Cancer Risk Assessment Tool, a computer program that is available from the NCI by calling the Cancer Information Service at 1-800-4-CANCER (1-800-422-6237, or TTY at 1-800-332-8615). This version of the Gail Model estimates only the risk of invasive breast cancer.

The Tyrer-Cuzick model incorporates both genetic and non-genetic factors.[87] A three generation pedigree is used to estimate the likelihood that an individual carries either a BRCA1/BRCA2 mutation or a hypothetical low penetrance gene. In addition, the model incorporates personal risk factors such as parity, body mass index, height, and age at menarche, menopause and first live birth. Both genetic and nongenetic factors are combined to develop a risk estimate. Although powerful, the model at the current time is less accessible to primary care providers than the Gail and Claus models. The BOADICEA model examines family history to estimate breast cancer risk, and also incorporates both BRCA1/2 and non-BRCA1/2 genetic risk factors.[88]

Other models incorporating breast density have been developed, but are not ready for clinical use.[89,90] In the future, models may be developed or refined to include such factors as breast density and other biomarkers.

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