APPENDIX III: RISK MEASUREMENT & ASSESSMENT: BREAST AND OVARIAN CANCER

Carolyn D. Farrell, MS, CNP, CGC

Risk: Definition

The purpose of this appendix is to provide the foundation for defining "risk", review the current status of knowledge in this area and list parameters known to be associated with increased inherited risk. However, within the spectrum of risk based on personal and family history, there is as yet no clear-cut delineation that specifically separates those likely to have a mutation from those likely to not. The purpose of these Guidelines is to assist the practitioner in the clinical management of persons with, or at increased risk for, breast and/or ovarian cancer. Risk is defined as "the possibility of loss or injury; a dangerous element or factor". From the cancer genetics perspective, the risk assessment process refers to evaluation of persons for the presence of an inherited factor, or factors, known to increase susceptibility for the development of cancer. Furthermore, the concept of risk extends to the potential transmission of such a gene, or genes, to offspring which places them at increased risk.¹

What constitutes increased risk? Risk thus incorporates the concept of a baseline existing "risk" that is "usual" or "acceptable", that exists for all, and that forms the basis for comparison to determine those at "increased risk". In assessing risk for breast/ovarian cancer, there is a subtle distinction between 1) determination of persons at, and factors associated with, increased risk for breast cancer due to the interaction of both genetic and environmental factors, and 2) determination of persons at increased risk for inheritance of a single gene mutation associated with increased risk for breast/ovarian cancer.

"Increased risk", in these Guidelines, will be used in the second sense. This definition of risk recognizes that an essential focus of this committee's effort is to address issues associated with genetic testing. It is recognized, however, that individuals at (or perceived to be at) increased risk will seek or be referred for genetic counseling, education and, in some cases, testing.

Risk Measurement:

Average risk: Breast cancer will affect 1 in 8 women in their lifetimes, for a background risk of 12%.² This figure represents an average of all females, thus incorporating risks for persons with varying individual and family histories. The "average" female, in the absence of a positive personal or family history, should be advised to follow the American Cancer Society guidelines for breast cancer screening. Genetic testing is not indicated for such women at this time.

Increased risk: Two models are currently used for breast cancer risk assessment. The Gail model, based on a study of over 30,000 women through the Breast Cancer Detection and Demonstration Project, was developed based on data indicating that the following factors are correlated with an increased risk for breast cancer: early age of menarche (<12 years), late menopause (>50 years), nulliparity or first live birth after age 30, positive family history of breast cancer (first degree relatives: parents, siblings, children), and history of previous biopsies.³ Further assessment of these risk factors in relation to a positive family history was studied by Colditz (1996) in a cohort of 89,132 women from the Nurses Health Study.⁴ For those with a positive family history, there was little benefit from later menarche, earlier age at first birth, or parity; in fact, pregnancy had an adverse effect. In contrast, those women with a negative family history had decreased risk associated with early pregnancy and multiple births. The Claus model was developed from the Cancer and Steroid Hormone population-based, case-control study involving 4730 patients with histologically documented breast cancer and 4688 matched controls. This model is based on the premise that the factor most relevant to individual risk for breast cancer is family history.⁵ The degree of risk is related to the number, the age, and the pattern of affected relatives in the family.

The limitations of these models include that they address breast cancer only, do not permit or have limited application for risk assessment of all persons with a positive personal or family history, partially incorporate a multifactorial perspective, cannot differentiate sporadic cases in a family, may not integrate the significance of bilateral disease, are based on Caucasian populations, and projected risks are based on observations and projections from human studies (albeit large scale).

A study by deSilva (1995) of 35,505 persons seen through the North East Scotland National Health Service Breast Screening Program pragmatically defined risk as greater than twice the age-related risk.⁶ The criteria used were based on family history information to identify persons with:

1. a first degree relative with bilateral breast cancer,
2. two first degree relatives with breast or ovarian cancer,
3. first degree relative with breast cancer diagnosed before age 40,
4. first or second degree male relative with breast cancer, and
5. an apparently dominant family history of breast cancer (three or more affected
   relatives in at least two generations).

In this population, 154 women and 289 of their relatives between the ages of 50 and 64 were identified. Julian-Reynier (1996) studied 206 consultees utilizing services of oncologists at six centers in France.⁷ "Risk" was defined by individual perception which ultimately was determined by family history.

Several other authors consider risk for heritable cancer increased when any one or more of the following are present:

1. early onset of cancer (younger than that in the general population, e.g., Winchester (1996) estimates that hereditary breast cancer accounts for 36-85% of
   patients diagnosed under age 30⁸),
2. bilateral disease or multiple primary tumors,
3. positive family history of breast and/or ovarian cancer1,
4. existence of a breast cancer associated genetic condition (such as Li-Fraumeni,
   Lynch II, Cowden, Peutz-Jeghers, or ataxia telangectasia), or
5. occurrence of a rare cancer in an individual not at known risk.^{9,10, 11}

Young age of onset of breast cancer, even in the absence of family history, has been demonstrated to be a risk factor for BRCA1 mutations. Langston (1996) studied 80 women diagnosed with breast cancer before age 35; six (7.5%) had BRCA1 mutations.¹²

In a report published by Frank et al (1997) concerning BRCA1 and BRCA2 sequence analysis of 335 high-risk women, the modeled probability of detecting a mutation in one of these two genes ranged from 25-89%¹³. This study involved women diagnosed with breast cancer before age 50, who had at least one first- or second-degree relative with breast or ovarian cancer. In a separate personal communication with staff of Myriad Genetics, preliminary data on analysis of persons with early onset breast cancer in the absence of a positive family history has suggested a mutation detection rate of approximately 10%.

Risk factors for ovarian cancer, according to the National Cancer Institute, include advancing age, nulliparity, North American or Northern European descent, personal history of endometrial, colon or breast cancer, and a family history of ovarian cancer.¹⁴ Hartge (1994) combined data from seven studies of 1122 cases and 5359 controls that supported an increased risk (4.4% by age 65) for ovarian cancer if a woman had a positive family history - defined as an affected mother or sister.¹⁵ Nguyen (1994) determined that an increased lifetime risk of ovarian cancer, ranging from 1.6% to 5-7%, existed in women with one or two affected first or second degree relatives.¹⁶ Piver (1993) reported that in 658 families with ovarian cancer, 49.5% involved a mother-daughter relationship, while 38.5% were sister-sister.¹⁷ Thus, this author concluded that the risk for inheritance of a breast/ovarian cancer gene is essentially limited to those with a positive personal and/or family history of breast and/or ovarian cancer, or with a genetic syndrome known to be associated with risk for ovarian cancer.

Risk Assessment:

Thus far two major genes, BRCA1¹⁸ and BRCA2¹⁹, and other less frequently involved genes such as (p53) and AT¹⁰, have been implicated in increased risk for the development of breast and/or ovarian cancer at an early age. Data have been based on studies of families with three or more affected persons with breast and/or ovarian cancer, usually at least one of whom had an early age of onset.²⁰ Cornelis (1995) found that diagnosis at a mean age of 45 was significant for linkage to chromosome 17 in the 13 families studied.²¹ In a population-based case-control study of ovarian cancer, Schildkraut (1988) found that the odds ratio for ovarian cancer in first- and second-degree relatives was 3.6 and 2.9, respectively.²² Takahashi (1995) studied 115 cases of epithelial ovarian cancer for mutations in BRCA1; seven mutations were identified, all of which were present in the germline of persons with a positive family or medical history.²³ Initial BRCA1 studies had indicated an up to 87% risk, by age 85, for the development of breast cancer, and a 40-60% risk for the development of ovarian cancer, in an individual who has a BRCA1 mutation.^{24, 25, 26} However, a more recent study by Struewing et al (1997) of 5318 persons of Ashkenazi Jewish ancestry in the Washington, DC area, suggests that these figures may be somewhat inflated. Based on analysis of the three most common mutations in BRCA1 and BRCA2 in this population, the lifetime risk for breast or ovarian cancer was 56% and 16%, respectively.²⁷

Over 38 different mutations were reported in BRCA1 by Shattuck-Eidens²⁸; these different genotypes need to be correlated with phenotypes to improve risk assessment. BRCA2 mutations may occur with similar frequency to those of BRCA1, yet the penetrance of the former may be less, or it may be more age-dependent. This concept is supported by Easton (1995) who studied families linked to chromosome 17q and found evidence for genetic heterogeneity of BRCA1 alleles conferring different levels of risk.²⁹ Neuhausen (1996) studied 61 breast/ovarian cancer families and found that 57% of women presumed affected because of the 1294del40 BRCA1 mutation had ovarian cancer, whereas only 14% had ovarian cancer if the mutation involved the splice-site of intron5.³⁰

A study by Schutte (1995) reported a homozygous deletion within the BRCA2 region in a pancreatic cancer family.³¹ Additionally, an increased frequency of prostate and colon cancer has been noted in families with breast and ovarian cancer, wherein a BRCA1 gene mutation exists. These findings suggest the need for further studies to determine if mutations within these genes increase the risk for other cancers (and if so, the genotype/phenotype correlations), or whether these findings are possibly due to bias of ascertainment or other confounding factors.

Male breast cancer is rare and accounts for fewer than 1% of breast cancer cases.³² However, it is another factor associated with inheritance of a breast cancer susceptibility gene, specifically BRCA2. BRCA2 mutations were found in 14% of 50 males with breast cancer in a study by Couch (1996); all but one had a positive family history.³³ Males with a BRCA2 mutation have a 5-10% lifetime risk for breast cancer. In contrast, BRCA1 mutations do not appear to be associated with an increased risk for male breast cancer. A study by Narod (1995) of 145 breast cancer families did not identify a BRCA1 mutation in any of 13 families with male breast cancer³⁴. However, Struewing (1995) reported one family with male breast cancer in his study wherein eight BRCA1 mutations were identified in 10 breast/ovarian cancer families.³⁵ This latter report may represent a sporadic case of male breast cancer.

Another issue is that of potential populations at risk. Preliminary research has suggested that about 1% of the Ashkenazi Jewish population carries a BRCA1 mutation, specifically 185delAG, which is associated with an increased risk for breast and ovarian cancer.^36,37 Subsequently, at least two other BRCA1 associated gene mutations have been documented to occur with an increased frequency in this population. Similarly, a mutation in BRCA2, 6174delT, occurs with a frequency of about 1%.³⁸ Struewing et al (1997) noted that the total frequency of three specific mutations in BRCA1 and BRCA2 in an unselected Ashkenazi population was 2.5%.²⁷ In a study of BRCA1 mutations in 52 unrelated families, comparing Jewish to non-Jewish, Berman (1996) found an incidence of 36% in affected persons of Jewish ancestry with a positive family history. In contrast, in non-Jewish families, the corresponding figure was 11%.³⁹ Furthermore, in non-Jewish families, mutation detection in an unaffected person with a positive family history was only 3%. Thus, a positive family history increases the likelihood of detecting a breast cancer susceptibility gene mutation, yet other factors such as affected status and age of onset are also relevant. However, even in the presence of these risk factors, breast cancer associated gene mutations may not exist or be detectable. Furthermore, it is difficult to interpret the meaning of the mutation in an unaffected person with a negative family history. Thus, at this time, genetic testing is neither recommended as a screening test for the general population, nor for persons of Ashkenazi Jewish ancestry, in the absence of a positive family history.

Using a statistical likelihood or threshold number for detecting a breast cancer associated gene mutation has been suggested as one approach to determining who would be eligible for genetic testing. This consideration has both practical and economic benefits, yet has significant limitations. In a statement adopted by the American Society of Clinical Oncologists in 1996, the recommendation for offering testing is that of a "strong family history of cancer or very early age of onset of disease"⁴⁰; the examples given essentially represent a greater than 10% chance of detecting a BRCA1 gene mutation. However, the use of a specific figure (for likelihood of detecting a mutation) as a guideline for recommending testing focuses the approach on testing itself, limits assessment, education and offering testing, and works from the assumption that only "positive" findings have significance. Additionally, the meaning of a "strong family history" and "early age of onset" are not absolutes. Shattuck-Eidens (1997)⁴¹ demonstrated that the likelihood of detecting a BRCA1 mutation was dependent not only on these variables, but upon other interdependent factors such as ethnic background, existence of multiple cancers in one individual, whether the cancer/s present were breast or ovarian or both, and the number of affected relatives. They studied 798 persons (representing this number of families) identified by referral to participating centers, who were considered to be at "elevated risk" based on positive family history, early age of onset of breast cancer and/or history of ovarian cancer. Deleterious BRCA1 mutations were identified in 102 (12.8%). Fifty new mutations were identified: 24 deleterious, 24 of unknown significance and two rare polymorphisms. In a subset of 71 persons identified as of Ashkenazi Jewish ancestry, BRCA1 mutations were identified in 24 cases; these involved only two mutations (185delAG and 5382 insC). Based on the data and analysis from this study, a method for evaluating probability of carrying a deleterious mutation within BRCA1 was formulated. These calculations are based upon: presence or absence of ovarian cancer, presence or absence of bilateral breast cancer, and the corresponding combinations of these in the patient; patient age at diagnosis; patient ethnicity (if Ashkenazi); and number of relatives with breast cancer only, ovarian cancer only, or both. This study is the largest and most comprehensive report of this nature thus far. However, it is limited in that the information derived is directly applicable only to affected individuals, the study did not include analysis for BRCA2 gene mutations, and although the BRCA1 gene analysis did involve full sequencing of all exons and intron-exon boundaries within BRCA1, the technology used could not detect mutations in regulatory regions or was limited by PCR-dependent probes. With regard to the Ashkenazi population, it appears from this study that analysis of affected persons for only the two reported BRCA1 mutations and sequencing of exon 11 would detect all mutation carriers. However, since ancestry was not stipulated for all 798 participants, it is not possible to determine the percent of participants who were of Ashkenazi ancestry, but were not reported as such, and whether any of them had a detectable mutation which was other than one of the two reported. Additionally, since BRCA2 testing was not reported as part of this study, it is not known what percentage of persons of Ashkenazi Jewish ancestry would have had detectable mutations within BRCA2, and further, if the mutation/s would have been of a common nature. Thus, the potential for limitations or misinterpretation of results in the absence of full sequencing of both BRCA1 and BRCA2.

Consistent with the above literature review regarding increased risk, eligibility requirements for breast cancer genetic susceptibility testing may include the following:

1. Persons with breast or ovarian cancer who have two or more first or second degree relatives (related through a single lineage) with breast or ovarian cancer.
2. Persons with breast or ovarian cancer who have one relative with breast cancer diagnosed at an early age (especially <45 years) or ovarian cancer diagnosed at any age.
3. Persons with breast or ovarian cancer diagnosed at an early age (premenopausal).
4. Persons with breast or ovarian cancer with multiple primary cancers or bilateral disease.
5. Men who developed breast cancer at any age.
6. Relatives of persons with documented mutations in either the BRCA1 or BRCA2 gene.⁴³
7. Persons with a family history of three or more relatives with breast or ovarian cancer, at least one of which is a first degree relative (through a single lineage).
8. Persons suspected to have a genetic disorder/syndrome associated with a known breast cancer associated gene.

If identification of potential risk for breast or ovarian cancer is extended to include populations at suspected increased risk, or with an increased frequency of specific mutations (although knowledge of the meaning of these mutations is limited), then consideration could be given to incorporating the following criterion into the definition of risk and eligibility:

9. Persons in populations at risk (e.g., Ashkenazi Jewish). However, at the present time, such testing is not indicated in unaffected patients with negative family histories.

Author's Notes:

• A family or personal history of cancers, other than breast or ovarian, warrants further evaluation, may represent increased risk, and may or may not be an indication for breast/ovarian or other cancer-associated gene mutation testing.

• If genetic testing is being considered, it is advisable to start with an affected family member in order to determine if there is an identifiable mutation. Without that basis, the ability to determine the significance of any finding in an unaffected individual is compromised.

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