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      Cancer as a Complex Phenotype: Pattern of Cancer Distribution within and beyond the Nuclear Family

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          The contribution of low-penetrant susceptibility variants to cancer is not clear. With the aim of searching for genetic factors that contribute to cancer at one or more sites in the body, we have analyzed familial aggregation of cancer in extended families based on all cancer cases diagnosed in Iceland over almost half a century.

          Methods and Findings

          We have estimated risk ratios (RRs) of cancer for first- and up to fifth-degree relatives both within and between all types of cancers diagnosed in Iceland from 1955 to 2002 by linking patient information from the Icelandic Cancer Registry to an extensive genealogical database, containing all living Icelanders and most of their ancestors since the settlement of Iceland.

          We evaluated the significance of the familial clustering for each relationship separately, all relationships combined (first- to fifth-degree relatives) and for close (first- and second-degree) and distant (third- to fifth-degree) relatives. Most cancer sites demonstrate a significantly increased RR for the same cancer, beyond the nuclear family. Significantly increased familial clustering between different cancer sites is also documented in both close and distant relatives. Some of these associations have been suggested previously but others not.


          We conclude that genetic factors are involved in the etiology of many cancers and that these factors are in some cases shared by different cancer sites. However, a significantly increased RR conferred upon mates of patients with cancer at some sites indicates that shared environment or nonrandom mating for certain risk factors also play a role in the familial clustering of cancer. Our results indicate that cancer is a complex, often non-site-specific disease for which increased risk extends beyond the nuclear family.


          It's not often that an entire nation's genealogy and cancer records are available. But they are in Iceland, and have been used to determine how often cancers occur in families

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          Most cited references 46

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          Revised Bethesda Guidelines for hereditary nonpolyposis colorectal cancer (Lynch syndrome) and microsatellite instability.

          Hereditary nonpolyposis colorectal cancer (HNPCC), also known as Lynch syndrome, is a common autosomal dominant syndrome characterized by early age at onset, neoplastic lesions, and microsatellite instability (MSI). Because cancers with MSI account for approximately 15% of all colorectal cancers and because of the need for a better understanding of the clinical and histologic manifestations of HNPCC, the National Cancer Institute hosted an international workshop on HNPCC in 1996, which led to the development of the Bethesda Guidelines for the identification of individuals with HNPCC who should be tested for MSI. To consider revision and improvement of the Bethesda Guidelines, another HNPCC workshop was held at the National Cancer Institute in Bethesda, MD, in 2002. In this commentary, we summarize the Workshop presentations on HNPCC and MSI testing; present the issues relating to the performance, sensitivity, and specificity of the Bethesda Guidelines; outline the revised Bethesda Guidelines for identifying individuals at risk for HNPCC; and recommend criteria for MSI testing.
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            Cancer risks in BRCA2 mutation carriers.

            Carriers of germline mutations in the BRCA2 gene are known to be at high risk of breast and ovarian cancers, but the risks of other cancers in mutation carriers are uncertain. We investigated these risks in 173 breast-ovarian cancer families with BRCA2 mutations identified at 20 centers in Europe and North America. Other cancer occurrence was determined in a final cohort of 3728 individuals, among whom 681 persons had breast or ovarian cancer and 3047 persons either were known mutation carriers, were first-degree relatives of known mutation carriers, or were first-degree relatives of breast or ovarian cancer patients. Incidence rates were compared with population-specific incidence rates, and relative risks (RRs) to carriers, together with 95% confidence intervals (CIs), were estimated by use of a maximum likelihood approach. Three hundred thirty-three other cancers occurred in this cohort. Statistically significant increases in risks were observed for prostate cancer (estimated RR = 4.65; 95% CI = 3.48-6.22), pancreatic cancer (RR = 3.51; 95% CI = 1. 87-6.58), gallbladder and bile duct cancer (RR = 4.97; 95% CI = 1. 50-16.52), stomach cancer (RR = 2.59; 95%CI = 1.46-4.61), and malignant melanoma (RR = 2.58; 95% CI = 1.28-5.17). The RR for prostate cancer for men below the age of 65 years was 7.33 (95% CI = 4.66-11.52). Among women who had already developed breast cancer, the cumulative risks of a second, contralateral breast cancer and of ovarian cancer by the age of 70 years were estimated to be 52.3% (95% CI = 41.7%-61.0%) and 15.9% (95% CI = 8.8%-22.5%), respectively. In addition to the large risks of breast and ovarian cancers, BRCA2 mutations may be associated with increased risks of several other cancers.
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              Systematic population-based assessment of cancer risk in first-degree relatives of cancer probands.

              Cancer has long been recognized to have a familial component. Elevated risks for cancers at the same site for relatives of cancer probands have been reported for both common cancers and a number of the rarer cancer sites. For a particular cancer site, however, the estimated risks to relatives have varied considerably depending on criteria for selection of probands, how cancers were determined in relatives, and overall study design. Not surprisingly, the estimated risks of other cancers in relatives of probands with cancer at a given site have been subject to even more variation. The aim of this study was to use the Utah Population Database resource to systematically study familial clustering of 28 distinct cancer site definitions among first-degree relatives (parents, siblings, and off-spring) of cancer probands. We estimated familial relative risks from the Utah Population Database by identifying all cases of cancer in these first-degree relatives. These observed values were compared with those expected based on cohort-specific internal rates calculated from 399,786 relatives of all individuals in the Utah Population Database known to have died in Utah. All sites showed an excess of cancers of the same site among relatives, with thyroid and colon cancers and lymphocytic leukemia showing the highest familial risks. When the analyses were restricted to cases with early ages at diagnosis, increased familial components for most cancer sites became evident. A significant difference in familial relative risk (FRR) between male (FRR = 4.04; 95% confidence interval [CI] = 3.13-5.07) and female (FRR = 2.24; 95% CI = 1.54-3.08) probands was found for colon cancer. Highly significant familial associations (one-sided; P < .001) were found among breast, colon, and prostate cancers and between breast and thyroid cancers. Statistically significant (one-sided, P < .01) associations were also found between tobacco-associated sites (lung, larynx, lip, and cervix). This study represents a unique comprehensive population-based study of familial cancer. The familial associations reported here will be useful in generating hypotheses about specific genetic and environmental factors that can be tested in genetic linkage and case-control studies.

                Author and article information

                Role: Academic Editor
                PLoS Med
                PLoS Medicine
                Public Library of Science (San Francisco, USA )
                December 2004
                28 December 2004
                : 1
                : 3
                1deCODE Genetics ReykjavikIceland
                2National University Hospital ReykjavikIceland
                Guy's King's and St. Thomas' School of Medicine United Kingdom
                Author notes

                Competing Interests: JB and SA have declared that no competing interests exist. LTA, ST, DFG, PS, KK, JRG, AK, UT, KS have stock in deCODE Genetics as well as equity interests.

                Author Contributions: LTA, ST, DFG, PS, KK, SA, JRG, JB, AK, UT, and KS designed the study. LTA, ST, DFG, PS, AK, and UT analyzed the data. LTA, ST, DFG, PS, KK, SA, JRG, JB, AK, UT, and KS contributed to writing the paper.

                *To whom correspondence should be addressed. E-mail: laufey.amundadottir@ 123456decode.is (LTA), E-mail: kari.stefansson@ 123456decode.is (KS)

                ¤1Current address: Keflavik County Hospital, Keflavik, Iceland

                Copyright: © 2004 Amundadottir et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited
                Research Article
                Genetics/Genomics/Gene Therapy



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