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1 Division of Molecular Genetic Epidemiology, German Cancer Research Center, Heidelberg, Germany, and 2 Department of Biosciences at Novum, Karolinska Institute, Huddinge, Sweden
| Abstract |
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age 30 years, and the third at age >60 years. The kappa test was used to assess the likelihood of an identical histology in two family members. The occurrence of hemangioblastoma was completely determined among the siblings, and the kappa value was 1.00. Meningiomas were also moderately ordered among the siblings, but astrocytomas were less determined. Many syndromes are known in which nervous system tumors are manifestations, including hemangioblastoma, recognized as part of von Hippel-Lindau disease. Yet, it is likely that many brain astrocytoma, meningioma, and mixed families represent yet unknown heritable conditions. | Introduction |
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10, 0.8, and 0.3/100,000, respectively (1)
. Histologically, the most common brain tumors are (in this order) astrocytomas of different kinds, meningiomas, neurinomas (schwannomas), ependymomas, and medulloblastomas; spinal tumors are meningiomas and neurinomas; peripheral nerve tumors are neurinomas, neurofibrosarcomas, and neuroblastomas (2)
. In Sweden, brain tumors are the most common childhood neoplasia, constituting some 7% of all diagnosed brain tumors (1)
. Brain tumors of children and young adults are preferentially pilocytic and diffuse astrocytomas, medulloblastomas, and ependymomas (2)
. Therapeutic irradiation and family history are the only established risk factors of nervous system tumors (3)
. Nervous system tumors are manifested in many rare cancer syndromes such as Li-Fraumeni, neurofibromatosis 1 and 2, von Hippel-Lindau, Turcot, and Gorlin (2
, 4, 5, 6)
. It is not known how large a fraction of nervous system tumors these syndromes account for; for childhood brain tumors, identified genetic conditions were thought to cover some 2% (7)
. Population-based family studies have mainly covered brain cancers or all nervous system tumors combined; familial risks in adults have been
1.81.9 in Sweden (8, 9, 10, 11, 12)
and Utah (13)
. However, no increase in familial glioma has been found in Iceland (14)
. No increased risk of brain cancer has been observed in parents of childhood brain cancer patients (15)
nor among offspring of survivors of childhood brain cancer (16)
. Here, we analyze the risk of familial nervous system tumors of any age and of defined histological type using the newest update of the nationwide Swedish Family-Cancer Database (17) . Compared with previous brain cancer studies from this Database, an extended population (offspring from year 1932 onwards compared with year 1935 earlier), more cancer cases (follow-up, including year 2000 compared with year 1996), and a more refined histological classification (covering 8 years compared with 4 years) are being used, allowing analysis by age of onset through parental and sibling probands. In the Database, family relationships and cancers were obtained from registered sources of practically complete coverage, reducing chances for bias.
| Subjects and Methods |
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SIRs were used to measure the cancer risks for offspring according to occurrence of cancers in their families. SIRs were calculated for offspring whose parent or sibling had the same concordant cancer, i.e., using parents or sibling as probands. Follow-up was started for each offspring at birth, immigration, or January 1, 1961, whichever came latest. Follow-up was terminated on diagnosis of first cancer, death, emigration, or the closing date of the study, December 31, 2000. When >2 affected offspring were found in any family, they were counted as independent event; however, this applied only to three families and had minimal effect on the results.
Parents ages were not limited but offspring were 068 years of age. All tumor IRs were based on the data in the Family-Cancer Database, and they are essentially similar to rates in the Swedish Cancer Registry. Rates were standardized to the European population. SIRs were calculated as the ratio of observed (O) to expected (E) number of cases. The expected numbers were calculated from 5-year-age-, sex-, tumor type-, period- (5-year bands), socioeconomic status- (six groups), and residential area- (three groups) specific standard IRs for all offspring lacking a family history (20) . Because >98% of all offspring lacked family history, the reference rate was essentially that for the whole population. CIs (95% CI) were calculated assuming a Poisson distribution (20) . Risks for siblings were calculated using the cohort method, described and discussed elsewhere (21) . In this method, sibships of two or more are included and all siblings contribute to cases and person years. Families with multiple affected individuals are ascertained at multiple times, and they are not independent, leading to too narrow CIs (approximately by a factor of 1.4; Ref. 22 ); no correction was done in the present article.
The kappa statistic was used as the measure of agreement between histologies: (observed proportion in agreement - expected proportion in agreement)/(1 - expected proportion in agreement; Ref. 22 ). The kappa can assume values between -1 and 1; 0 shows a complete chance occurrence, and -1 or 1 show a complete concordance or discordance. Values between 0.40 and 0.60 are considered moderately concordant. We only present positive values of the kappa because only the concordance of histological types is relevant in this context.
| Results |
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Kappa test was applied to assess the histological concordance of brain tumors (data not shown). Hemangioblastoma showed the highest kappa, 0.85 between offspring and parents and 1.00 between siblings. Kappa values of meningioma and astrocytoma among offspring and parents were not histology specific and they ranged between 0.28 and 0.36. However, among siblings, histology-specific tumors showed the highest kappa values, 0.46 for meningioma and 0.37 for astrocytoma. Among offspring and parents, kappa values were 0.27 for neurinoma and meningioma.
In the Database, five families had a parent and 2 offspring affected by nervous system tumors. In two families, all patients had an astrocytoma; in the remaining three families, the affected individuals had tumors of different histologies, two of which included one spinal tumor. No unambiguous assignment of these patients to a known syndrome was possible.
| Discussion |
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The overall familial risk for nervous system tumors of 1.70 in offspring of parental nervous system tumor patients is in line with earlier publications on brain tumors from this and other sources (8, 9, 10, 11, 12, 13 , 25) . Although the present study was the largest yet published, we were unable to note overall familial risks for intraspinal and peripheral nerve tumors. In the discussion below, we only take up the new findings of the present study and refer a general discussion to our earlier publications.
Because of the large numbers, we were able to describe age-specific familial risks to some extent. In all nervous system cancer, the risk was maximal in the twenties among siblings. In offspring of affected parents, the maximum was broader, covering ages 1039 years and a late onset maximum at ages > 60 years. In astrocytoma, three maxima were noted, one in childhood, <10 years, the second
3039 years, and the third one at >60 years. These distinct components could imply three different underlying causes. Astrocytomas occur early in tuberous sclerosis, and this condition may contribute to the childhood familial risk; however, because parental tumors were diagnosed at an older age and include also neurinomas and neurofibrosarcomas, the etiology is likely to be heterogeneous (2)
. Li-Fraumeni syndrome is characterized by occurrence of astrocytomas in the early thirties as the mean age but with a wide distribution, and it is probably part of the second familial component; Turcot syndrome could also contribute to this or the late onset familial component (2)
. Data from the Swedish glioma cohort suggest different etiologies for low- and high-grade gliomas (9)
. Furthermore, the familial risk was higher in low-grade glioma compared with the high-grade disease, a finding that we have also observed when analyzing familial risks in histology specific cancers (19)
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The kappa test was used to study consistency of occurrence of a defined histology in tumors of different family members between offspring and parents and between siblings. The test statistic will approach 1.00 if the pairs of individuals always present with the identical histological type of tumor, i.e., the histology is completely determined for reasons such as heritability. Hemangioblastoma offered a proof of the principle. It showed a high kappa value of 0.85 between offspring and parents and 1.00 between siblings, supporting nonrandom, heritable causation. A kappa value 0.4 is considered of a moderately ordered occurrence, and among siblings, meningioma showed a value of 0.46 and astrocytoma 0.37. Between offspring and parents, concordant meningioma gave a kappa of 0.28 and astrocytoma 0.29, but a higher kappa, 0.36, was noted when these two histologies appeared in the same families. Lower kappa values between offspring and parents than between siblings, also noted for hemangioblastoma, may be attributable to a more defined disease phenotype within one generation than between two generations, relating to age and calendar time differences. The data suggest that familial meningioma has a heritable etiology and neurofibromatosis 2 is a known cause of such a clustering (2) . However, in this condition, gliomas are located primarily in the spine and not in the brain, as the present results show, suggesting other contributing causes. In the present study, concordant meningiomas showed a higher familial risk than concordant astrocytomas, 3.06 and 2.19 through parental and 4.41 and 3.20 through sibling probands, respectively. The data suggest furthermore that some meningiomas and astrocytomas share a heritable etiology, although the kappa values were low among siblings, but these were based to small numbers. A co-occurrence of these tumors has also been observed in a Finnish study (26) .
In summary, the present data suggest discrete familial components in brain astrocytoma and meningioma and familial coaggregation of these tumors in the same families. However, to what extent the familial aggregation can be explained by known heritable causes cannot be solved by epidemiological means alone and mutation analysis in the affected families is required. Overall, the clustering of many types of nervous system tumors in single families suggests that nervous system tumors present in multiple phenotypes, in analogy to the known syndromes and the complex results from segregation analysis on glioma (9 , 27) . Multiple phenotypes and heterogeneous etiologies are major challenges to gene identification efforts.
| Acknowledgments |
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| Footnotes |
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Requests for reprints: Kari Hemminki, Division of Molecular Genetic Epidemiology, German Cancer Research Center (DKFZ), Im Neuenheimer Feld 580, 69120 Heidelberg, Germany. Phone: 49-6221-421800; Fax: 49-6221-421810; E-mail: kari.hemminki{at}cnt.ki.se
3 The abbreviations used are: ICD, International Classification of Diseases; SNOMED, Systematized Nomenclature of Medicine; SIR, standardized incidence ratio; CI, confidence interval; IR, incidence rate. ![]()
4 Internet address: http://snomed.org. ![]()
Received 5/20/03; revised 7/24/03; accepted 7/30/03.
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