Is Hereditary Site-Specific Ovarian Cancer aDistinct Genetic Condition?

Alexander Liede,1,2 Patricia N. Tonin,3 Chia Chia Sun,2 Corinne Serruya,3 Mary B. Daly,4Steven A. Narod,1* and William D. Foulkes3,5

1The Centre for Research in Women’s Health, University of Toronto, Toronto, Ontario, Canada2Division of Preventive Oncology, The Ontario Cancer Treatment and Research Foundation,Toronto, Ontario, Canada

3Division of Medical Genetics, Department of Medicine, Montreal General Hospital, McGill University,Montreal, Quebec, Canada

4Fox Chase Cancer Center, Cheltenham, Pennsylvania5Cancer Prevention Research Unit, Sir MB Davis Jewish General Hospital, Montreal, Quebec, Canada

It is not clear if hereditary site-specificovarian cancer exists as a genetic entity dis-tinct from the hereditary breast–ovariancancer syndrome. We have identified a largeAshkenazi Jewish kindred with 8 cases ofovarian carcinoma and no cases of breastcancer. Initially, linkage analysis for thiskindred generated a negative LOD score toBRCA1, but subsequent mutation and hap-lotype analysis of key individuals demon-strated a BRCA1 185delAG mutation segre-gating with all but 1 of the ovarian cancercases. This observation has important impli-cations for genetic counselling of familieswith site-specific ovarian cancer. Heredi-tary site-specific ovarian cancer is likely tobe a variant of the hereditary breast–ovarian cancer syndrome, attributable to ei-ther BRCA1 or BRCA2. We consider womenfrom these families to be at increased risk ofbreast cancer and counsel them accord-ingly. Am. J. Med. Genet. 75:55–58, 1998.© 1998 Wiley-Liss, Inc.

KEY WORDS: site-specific ovarian cancer;BRCA1; hereditary ovariancancer; ovarian carcinoma;185delAG

INTRODUCTIONSeveral genes have been identified which play a role

in ovarian cancer susceptibility. Three hereditary ovar-ian cancer syndromes have been delineated based onthe clinical presentation of cancer at specific sites in

relatives: (1) hereditary site-specific ovarian cancer, (2)the hereditary breast–ovarian cancer syndrome, and(3) hereditary nonpolyposis colorectal cancer (HNPCC)[Lynch et al., 1986]. Most women with hereditary ovar-ian cancer are from families belonging to the breast–ovarian cancer syndrome. Two cancer susceptibilitygenes, BRCA1 and BRCA2, account for most familieswith multiple cases of breast and ovarian cancer[Narod et al., 1995a]. Women belonging to HNPCCfamilies are at an increased risk of ovarian cancer, al-though the DNA mismatch repair genes, hMLH1 andhMSH2, account for only 1% of ovarian cancer cases[Vasen et al., 1989; Watson and Lynch, 1993].

It has not yet been proven that there is a distinctgenetic basis to site-specific ovarian cancer becausemost cancer families this type have been attributed toBRCA1 and BRCA2 [Foulkes et al., 1995; Gayther etal., 1995; Shattuck-Eidens et al., 1995; Steichen-Gersdorf et al., 1994]. A family with 3 or more cases ofinvasive epithelial ovarian cancer at any age and nocase of breast cancer diagnosed before age 50 qualifiesas a site-specific ovarian cancer family [Steichen-Gersdorf et al., 1994]. However, a gene that predis-poses to ovarian cancer in the absence of breast cancerhas not been identified. Steichen-Gersdorf et al. [1994]reported 9 families with multiple cases of ovarian can-cer, 7 of which were positive for linkage to BRCA1. Thelargest family had 6 cases of ovarian cancer. Gaytherand Friedman (personal communication) identifiedBRCA2 mutations in 5 site-specific ovarian cancerfamilies, 3 of which have been reported [1997].

Mutations in the BRCA1 and BRCA2 genes confer anelevated risk for both breast and ovarian cancer. Therisk of ovarian cancer in BRCA2-mutation carriers isprobably less than in those with inherited BRCA1 mu-tations [Wooster et al., 1994]. Recent evidence hasidentified an ovarian cancer-cluster region in exon 11of BRCA2 with a higher risk of ovarian cancer [Gaytheret al., 1997]. The presence of a case of ovarian cancer ina breast cancer pedigree increases the probability thatsuch a family has a BRCA1 mutation [Narod et al.,

Contract grant sponsor: CRS/MRC of Canada.*Correspondence to: Dr. Steven A. Narod, The Centre for Re-

search in Women’s Health, 790 Bay Street, Suite 750A, Toronto,Ontario M5G 1N8, Canada. E-mail: narod@ftn.net

Received 2 April 1997; Accepted 28 July 1997

American Journal of Medical Genetics 75:55–58 (1998)

© 1998 Wiley-Liss, Inc.

1995a; Tonin et al., 1996]. Risk estimates derived forBRCA1- and BRCA2-predisposing mutations to datehave largely been based on retrospective studies ofhigh-risk families with great potential for ascertain-ment bias. A recent study by Struewing et al. [1997] on5318 unselected Ashkenazi Jewish individuals esti-mated breast and ovarian cancer risks associated withspecific BRCA1 and BRCA2 mutations to be lower thanpreviously reported.

We present findings on a large family with 8 cases ofovarian cancer and no case of breast cancer and discusspossible genetic and nongenetic factors implicated inthe atypical expression of a BRCA1 mutation in thisfamily.

FAMILY 483

Family 483 (Fig. 1) is of Ashkenazi Jewish descentand was ascertained in Eastern Canada. This familyincludes 8 cases of ovarian carcinoma over 4 genera-tions and no case of breast cancer. The age of onset ofthe ovarian cancers was 45–64 years. All cases havebeen confirmed by review of pathology reports, deathcertificates, or hospital records. Linkage analysis to17q at the BRCA1 locus was performed by using poly-morphic microsatellite markers, as shown in Figure 1:D17S855, D17S1323, D17S1322, D17S1327 andD17S1326 (3 intragenic and 2 100 kb distal of BRCA1,respectively). Results from haplotype analysis revealedthat individual 68, who developed serous papillary ad-

enocarcinoma of the ovary at age 46 years, does notshare a common haplotype with her cousin individual46, who was diagnosed with ovarian carcinoma at age45 years. In particular, individual 46 carries the hap-lotype consistent with a 185delAG BRCA1 mutation[Simard et al., 1994]. Direct sequencing of DNA fromthese individuals confirmed that individual 46 inher-ited a 185delAG mutation, whereas individual 68 didnot and was likely to be a sporadic case. Individual 66,her unaffected mother, did not carry the mutation. Par-ents of individual 46 are unaffected; her paternalgrandmother died of ovarian cancer at age 49 years.After the 185delAG mutation was identified for indi-vidual 46, further mutation analysis on other familymembers supported the segregation of the BRCA1 mu-tation with ovarian cancer in family 483.

Individual 68 was diagnosed with ovarian cancer atage 46 years but is now considered to be a phenocopybecause she did not inherit the 185delAG mutation.Subsequent mutation analyses excluded the two othercommon Ashkenazi Jewish mutations in BRCA1(5382insC) and BRCA2 (6174delT) for her. This helpsrule out paternal transmission of a common breast–ovarian cancer susceptibility gene [Roa et al., 1996;Tonin et al., 1996]. However, the father of individual 68was diagnosed with cancer of the descending colon at59 years and the paternal uncle with colon cancer at 64years. Although this is not sufficient to meet the Am-sterdam criteria for HNPCC, a mutated allele of a pa-

Fig. 1. Pedigree of family 483. Diamond symbols have been used to maintain the anonymity of the individuals tested. Black circles indicate affectedwomen, and black squares indicate affected men. Diagonal slash indicates deceased members. Individual identification numbers appear directly belowsymbols. Ov, ovarian cancer; Br, breast cancer; Co, colorectal cancer. The numbers following the abbreviations indicate ages of diagnosis. The numbersvertically below the individual symbols indicate the marker alleles arranged into haplotypes. Haplotypes in brackets are inferred. The haplotypeassociated with BRCA1 185delAG mutation is 6-3-3-3-10, shown in box. The plus signs indicate the presence of the BRCA1 185delAG mutation for theindividuals tested. The minus signs indicate the absence of the 3 common mutations of BRCA1 (185delAG, 5382insC) and BRCA2 (6174delT) for theAshkenazi Jewish population.

56 Liede et al.

ternally derived cancer gene could potentially havebeen inherited, conferring an elevated risk of colorectaland ovarian cancer.

In hereditary ovarian cancer families, the option ofprophylactic oophorectomy is considered for womenwho are BRCA1 mutation carriers after the age of 35years or once childbearing is complete. Initially, indi-vidual 66 was given a high risk of developing ovariancancer and was recommended to have prophylactic oo-phorectomy because the pedigree analysis placed heras an obligate carrier for an ovarian cancer-susceptibil-ity gene. The surgery was cancelled when results ofmutation analysis became available. Two of her daugh-ters (individuals 78 and 72) and other relatives hadpreviously undergone prophylactic oophorectomies onthe basis of the strong family history of ovarian cancer.Now that carrier detection is possible in this family,some of these operations can be avoided.

DISCUSSIONImplications for Genetic Counselling

It is not clear why the women carrying the BRCA1185delAG mutation in family 483 developed ovariancancer and not breast cancer. There are several pos-sible explanations for the variability in expression ofBRCA1 within and between families, including (1)chance clustering, (2) the random accumulation of mu-tations in other critical genes, (3) environmental fac-tors, (4) hormonal factors, and (5) the influence of al-lelic variations in other genes on the BRCA1 pheno-type.

Based on the number of mutation carriers in thisfamily, we expect 5–6 cases of breast cancer associatedwith the 185delAG mutation. Struewing et al. [1997]estimated the risk of breast and ovarian cancer associ-ated with three specific mutations of BRCA1(185delAG, 5382insC) and BRCA2 (6174delT). Of 5,318Ashkenazi Jewish individuals tested, 120 carriers wereidentified, and a 56% risk of breast cancer and a 16%risk of ovarian cancer to 70 years was estimated. Theatypical expression of the BRCA1 185delAG mutationin family 483 is unexpected if only 1 in 6 (16%) carriersare expected to develop ovarian cancer by 70 years.

Differences in ovarian cancer risks between familiesmay be due to either the effect of other genes unlinkedto BRCA1 or shared environmental factors that modifythe risk. At least 5 women with BRCA1-associatedovarian cancer in family 483 were reported as beingeither moderate (1–5 packs per week) or heavy (>5packs per week) smokers. This finding raises the pos-sibility of an association between smoking and an in-creased susceptibility to ovarian cancer or a decreasedsusceptibility to breast cancer in BRCA1 carriers.

The possibility of a modifying gene or genes influenc-ing variation in penetrance of the BRCA1 gene is alsoplausible. The first modifying gene for BRCA1 wasidentified in a recent study of 307 BRCA1 carriers from79 families. Phelan et al. [1996] demonstrated that thepresence of a rare allele of the HRAS1 proto-oncogeneincreases the risk of ovarian cancer as compared withBRCA1 carriers who had two common alleles (OR 42.11, P 4 0.015). However, the HRAS1 gene is on chro-

mosome 11p15.5 and is not expected to segregate withthe BRCA1-associated ovarian cancer susceptibility infamily 483.

Narod et al. [1995b] studied reproductive historieson 333 women who were identified as BRCA1 mutationcarriers from 28 North American families. Women withmultiple parity were at increased risk of ovarian can-cer, but there also appeared to be a protective effect ofa late birth, suggesting that both hormonal and geneticfactors influence the penetrance of the BRCA1 gene.The likelihood of parity and late childbirth relating tothe 7 BRCA1-associated ovarian cancer cases of family483 is minimal because the carrier women had 3 orfewer children each.

There is no consensus as to whether cancer risk es-timates for breast and ovarian cancer should be modi-fied for ovarian-only or breast-only families withBRCA1 mutations. Although there has been no case ofbreast cancer in family 483, the women who carry the185delAG mutation were advised that they are at a80–90% lifetime risk of developing breast cancer [Eas-ton et al., 1993, 1995]. We feel that it is premature tocounsel these women that they are not at a signifi-cantly increased risk of breast cancer until the geneticand nongenetic factors that play a role in tumourigen-esis in mutation carriers are better understood. Wecurrently counsel women belonging to families with 3or more cases of ovarian cancer that they are at in-creased risk of developing breast cancer. Conversely,we advise families with 3 or more cases of early-onsetbreast cancer that they are at increased risk of devel-oping ovarian cancer.

Genotype–Phenotype Correlations for BRCA1Mutations at 185delAG

In other hereditary cancer syndromes, it has beendifficult to predict phenotype from genotype. In HN-PCC, this led to the questioning of Lynch I and II asuseful prognostic groups to designate colorectal-specific and extraintestinal cancer risk, respectively.However, in familial adenomatous polyposis (FAP), theposition or type of mutation in the APC gene is moder-ately predictive of the gastrointestinal and ophthalmo-logic phenotypes [Caspari et al., 1994; Olshwang et al.,1993]. The ovarian cancer risk conferred by differentBRCA1 mutations may differ substantially [Easton etal., 1995], i.e., mutations to the 38 end of BRCA1 confera reduced risk of ovarian cancer [Gayther et al., 1995].In a study of common BRCA1 mutations found in Ash-kenazi Jewish families with breast–ovarian cancer, To-nin et al. [1996] observed that the average number ofcases of ovarian cancer was slightly higher in familieswith the 185delAG mutation (58 mutation) than inthose with the 5382insC mutation (38 mutation). Theissue of mutation-specific penetrances for the BRCA1gene remains unresolved.

The clinical expression of BRCA1 varies from familyto family as well as within families [Easton et al.,1994]. These differences may be due in part to differentmutant BRCA1 alleles associated with different de-grees of penetrance. Ford et al. [1995] hypothesized

Hereditary Site-Specific Ovarian Cancer 57

two classes of susceptibility alleles in which one alleleconferred an 87% risk of ovarian cancer and a 71% riskof breast cancer to age 70 years, and the other alleleconferred a risk of 18% for ovarian cancer and 86% forbreast cancer to age 70 years. Large site-specific ovar-ian cancer families such as 483, with mutations at the58 end of BRCA1, support such heterogeneity models.

Does Site-Specific Ovarian Carcinoma Exist?

Steichen-Gersdorf et al. [1994] reported 7 familieswith multiple cases of ovarian cancer who were positivefor linkage to BRCA1. It is known that the occurrenceof one ovarian cancer within a breast cancer pedigree isa good indicator that such an aggregation of breastcancer is more likely to be due to a BRCA1 mutation.Two or more cases of ovarian cancer elevates the prob-ability to 0.91 [Narod et al., 1995a]. The 5 hereditaryovarian cancer families characterized with BRCA2 mu-tations by Gayther et al. (personal communication,1997), however, suggest that site-specific ovarian can-cer may also be due to BRCA2. Family 483 is a heredi-tary site-specific ovarian cancer family that did notshow linkage to BRCA1 and suggested heterogeneity.However, mutation analysis eliminated this possibil-ity.

In conclusion, it has not yet been shown that there isa distinct site-specific ovarian cancer syndrome sepa-rate from the breast–ovarian cancer syndrome, and weconclude that most cancers in this type of family will beattributable to BRCA1 and BRCA2.

ACKNOWLEDGMENTS

We thank family members of 483 for allowing us topublish this report, and we express our sympathies forthe two women who died in 1996 of ovarian cancer. Wethank Simon Gayther and colleagues for access to un-published data and France Dion, Josephine Costalos,Maria Galvez, Roxana Moslehi, and Gordon Glendonfor technical support. Patricia N. Tonin is a CRS/MRCof Canada scholar.

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