Systematic population-based assessment of cancer risk in first-degree relatives of cancer probands

Evidence for autosomal dominant inheritance of prostate cancer

A family-history cancer survey was conducted on 5,486 men who underwent a radical prostatectomy, for clinically localized prostate cancer, in the Department of Urology at the Mayo Clinic during 1966-95; 4,288 men responded to the survey. Complex segregation analysis was performed to assess the genetic basis of age at diagnosis and the familial clustering of prostate cancer. For the total group, no single-gene model of inheritance clearly explained familial clustering of disease, which could be partly explained by lack of Hardy-Weinberg equilibrium, with an excess of homozygotes. After accounting for deviations from Hardy-Weinberg equilibrium, the best-fitting model that explained the familial aggregation and age at diagnosis was a rare autosomal dominant susceptibility gene, and this model fitted best when probands were diagnosed at <60 years of age. The model predicts that the frequency of the susceptibility gene in the population is .006 and that the risk of prostate cancer by age 85 years is 89% among carriers of the gene and 3% among noncarriers. A strength of our study is its large size, such that genetic models could be fitted within strata defined by the age of the proband. Although the autosomal dominant model was consistently the best model, the parameter estimates differed somewhat (P=.03) across the different age groups, suggesting genetic heterogeneity. Additional evidence that the hereditary basis of prostate cancer is likely to be genetically complex was provided by the following: (1) there was a significantly elevated age-adjusted risk of prostate cancer among brothers of probands, compared with their fathers (relative risk 1.5 [95% confidence interval 1.4-1.7]); (2) the autosomal dominant model predicted an excess of homozygotes, over that predicted by Hardy-Weinberg equilibrium; and (3) the model-predicted risk of prostate cancer among relatives was inadequate when probands were diagnosed at age >=70 years.

Segregation analysis of epithelial ovarian cancer in Finland

Epithelial ovarian cancer is known to aggregate in families. The dominantly inherited ovarian cancer predisposing genes, BRCA1, BRCA2 and genes involved in the hereditary non-polyposis colorectal cancer (HNPCC) syndrome, have recently been identified. However, in the majority of families with more than one case of ovarian cancer, dominant inheritance cannot be recognized. We investigated familial clustering of epithelial ovarian cancer in a population-based sample of 663 Finnish ovarian cancer patients. A segregation analysis with the POINTER software was conducted on the 937 nuclear families from these 663 pedigrees. The major gene model was favoured, and the sporadic and multifactorial models were strongly rejected. In the studied population, the best fitting model was a recessive mode of inheritance, and 8% of ovarian cancer patients were estimated to be homozygous for the deleterious genotype. This evidence for recessively inherited ovarian cancer predisposition should be interpreted cautiously, as the analysis is subject to certain errors, which are discussed in the article. Results of this analysis, however, strongly emphasize the role of genetic factors in all familial aggregation of epithelial ovarian cancer.

A systematic review and meta-analysis of family history and risk of ovarian cancer

OBJECTIVE

To estimate the relative risk and lifetime risk of ovarian cancer in women with various categories of family history.

DESIGN

A meta-analysis of all published case-control and cohort studies.

METHODS

Pooled relative risk estimates were calculated for the case control studies, using the Mantel-Haenzel method. These estimates were combined with the relative risks from the cohort studies. The pooled estimates of relative risk were used to estimate lifetime risks of ovarian cancer from age 15 up to age 75, for various categories of family history.

MAIN OUTCOME MEASURES

Relative risks and lifetime risks of developing ovarian cancer were calculated for the categories of women with 1. an affected first degree relative; 2. an affected mother; 3. an affected sister; and 4. women with more than one affected relative.

RESULTS

The relative risk to first degree relatives is 3.1 (95% CI 2.6-3.7). There is some evidence that this relative risk declines with age. The relative risk to mothers of cases 1.1 (95% CI 0.8-1.6) was lower than the relative risks to sisters: 3.8 (95% CI 2.9-5.1), and daughters: 6.0 (95% CI 3.0-11.9); the explanation of this difference is unclear.

CONCLUSIONS

Women with a family history of ovarian cancer have a substantially higher risk of developing ovarian cancer compared with women without such a history. However the risk is small for most categories of family history, except for the small number of individuals who have more than one affected relative.

The detection of K-ras mutations in colorectal cancer using the amplification-refractory mutation system

A total of 301 colorectal carcinoma (CRC) archival samples were analysed using the amplification-refractory mutation system (ARMS). Each sample was examined to determine the mutation status of codons 12 and 13 of the K-ras oncogene. The results from direct DNA sequence analysis carried out on 30 of the samples differed from the ARMS result in almost 50% of the cases as a result of the relative excess of wild-type to mutated DNA sequences. To assess the validity of the ARMS data, the polymerase chain reaction (PCR) was used to generate an amplicon from K-ras exon 1 from 23 of the samples. The PCR amplicons were cloned and sequenced, and the DNA sequence analysis of the cloned material was in agreement with the ARMS results in all but one case. This case represented a tumour that exhibited a five-nucleotide reversed inversion. The cloned sequence data confirm the sensitivity and specificity of the individual ARMS reactions and that it is possible in certain cases to detect additional, more complex, sequence variations.

Linkage analysis of chromosome 1q markers in 136 prostate cancer families. The Cancer Research Campaign/British Prostate Group U.K. Familial Prostate Cancer Study Collaborators

Prostate cancer shows evidence of familial aggregation, particularly at young ages at diagnosis, but the inherited basis of familial prostate cancer is poorly understood. Smith et al. recently found evidence of linkage to markers on 1q, at a locus designated "HPC1," in 91 families with multiple cases of early-onset prostate cancer. Using both parametric and nonparametric methods, we attempted to confirm this finding, in 60 affected related pairs and in 76 families with three or more cases of prostate cancer, but we found no significant evidence of linkage. The estimated proportion of linked families, under a standard autosomal dominant model, was 4%, with an upper 95% confidence limit of 31%. We conclude that the HPC1 locus is responsible for only a minority of familial prostate cancer cases and that it is likely to be most important in families with at least four cases of the disease.

Microsatellite instability in female non-small-cell lung cancer patients with familial clustering of malignancy

There is accumulating evidence of an increased risk of familial clustering of cancer in the first-degree relatives of lung cancer probands. However, no explanation has been proposed for these epidemiological data. We reviewed 379 female non-small-cell lung cancer (NSCLC) patients to obtain their family histories of malignancy. Among them, nine female NSCLC patients with three or more relatives diagnosed with malignancy and 28 control patients without a family history of malignancy were selected to be analysed for instability at six different microsatellite loci. We observed microsatellite instability (MSI) more frequently in the patients with three or more family histories of malignancy (six out of nine, 67%) than the control patients (5 out of 28, 18%). The incidence of MSI in the former was significantly higher than that in the control (P=0.011: Fisher's exact test). We detected no significant difference in clinicopathological characteristics between the cases with MSI and those without MSI, except for their family histories of cancer. Our results show that a significantly higher rate of MSI is associated with familial clustering of malignancy. MSI could be one of the underlying mechanisms for familial clustering of malignancy in female NSCLC patients.

Family history of cancer and risk of colorectal cancer in Italy

Subjects with a family history of colorectal cancer (CRC) are at increased risk of CRC, but quantification of the risk in different populations, the possible differences in risk according to localization of the cancer and the association of family history of other cancers with CRC risk are still open issues. We have therefore analysed data from a multicentric case-control study conducted in six Italian areas between 1992 and 1996 of 1225 incident cases of colon cancer, 728 cases of rectal cancer and 4154 controls admitted for acute conditions to the same network of hospitals as the cases. Unconditional logistic regression models including terms for gender, age, study centre, years of education and number of siblings were used to estimate the odds ratios (ORs) of CRC according to various aspects of history of CRC and other cancers in first-degree relatives. The OR for family history of CRC was 3.2 (95% confidence interval, CI, 2.5-4.1) for colon cancer and 2.2 (95% CI 1.6-3.1) for rectal cancer. Colon cancer was significantly associated with a family history of stomach (OR 1.4), bone (OR 2.1) and kidney (OR 2.3) cancers, while rectal cancer was significantly associated with a family history of lymphomas (OR 2.8). There was a 30% higher risk of colon and rectal cancer in subjects with a family history of any cancer, excluding intestine. The ORs for family history of CRC were 5.2 for colon and 6.3 for rectum when the proband's age was below 45 years. The ORs were similar when the affected relative was a parent or a sibling and in different strata of age of relative(s). For subjects with two or more first-degree relatives with CRC, the risk was 6.9 for the right colon, 5.8 for the transverse and descending colon, 3.8 for the sigma, 3.2 for the rectosigmoid junction and 1.9 for the rectum. This study confirms that a family history of CRC in first-degree relatives increases the risk of both colon and rectal cancer, the association being stronger at younger ages and for right colon.

Risks of breast and testicular cancers in young adult twins in England and Wales: evidence on prenatal and genetic aetiology

BACKGROUND

Aetiology of breast and testicular cancers may have prenatal factors, possibly exposure of the fetus to high concentrations of maternal oestrogen. Dizygotic twinning probably involves high hormone concentrations, and therefore, dizygotic twins might be at raised risk of these cancers. The aetiologies of breast and testicular cancers have genetic components, for breast cancer, especially at younger ages. Twins of these probands may, therefore, be at high risk. We investigated risk in twins of patients with breast cancer at young ages or with testicular cancer.

METHODS

We identified twins with breast cancer incident at ages younger than 45 years and with incident testicular cancer in England and Wales during 1971-89 by cross-matching national cancer-registration and births records. We determined zygosity by questionnaires to the patients. The twins of probands were followed up for cancer incidence and death. We analysed risks of breast and testicular cancer in dizygotic twins compared with monozygotic twins, and in monozygotic and dizygotic twins of probands.

FINDINGS

We identified 500 twins with breast cancer and 194 with testicular cancer. We found a non-significantly raised risk of breast cancer in dizygotic compared with monozygotic twins younger than 30 years (odds ratio 2.3 [95% CI 0.9-5.9]) but not older. The overall risk of testicular cancer was significantly higher in dizygotic twins than in monozygotic twins (1.5 [1.1-2.2]) consequent on a risk for seminomas was high (3.2 [1.6-6.5]; p = 0.001). Risk of breast cancer was significantly raised in female twins of probands (standardised incidence ratio 7.7 [4.9-12.2], p < 0.001). The relative risk of breast cancer was 34.7 (9.5-126.5) in monozygotic twins of women in whom breast cancer had occurred before age 35 years. The cumulative risk of breast cancer for these twins by age 40 years was 29% (13-56). The relative risk of testicular cancer was 37.5 (12.3-115.6) in twins of men with testicular cancer. The cumulative risk by age 40 years in monozygotic twins of men with testicular cancer was 14% (4-46).

INTERPRETATION

The higher risks of these cancers in dizygotic than in monozygotic twins support a prenatal aetiology, and are compatible with aetiology related to raised maternal concentrations of free, unbound oestrogens. The results for twins of probands have implications for genetic aetiology; appropriate clinical action for monozygotic twins needs consideration.

Heredity and prostate cancer: a study of World War II veteran twins

BACKGROUND

Increased risk of prostate cancer among men with a family history of the disease has been observed in several epidemiological studies, and family studies have identified hereditary prostate cancer characterized by early onset and autosomal dominant inheritance.

METHODS

In this study, we examine prostate cancer heritability among twins in the NAS-NRC Twin Registry, with cases ascertained from a number of sources: recent telephone interviews, Medicare and Department of Veterans Affairs hospitalizations, previous mail questionnaires, and death certificates. A total of 1,009 prostate cancer cases were identified among the cohort of 31,848 veteran twins born in the years 1917-1927.

RESULTS

Probandwise concordance for prostate cancer was substantially higher among monozygous twin pairs, 27.1%, than among dizygous twin pairs, 7.1% (P < 0.001).

CONCLUSIONS

These data suggest that genetic influences account for approximately 57%, and environmental influences for 43%, of the variability in twin liability for prostate cancer.

Familial Hodgkin's and non-Hodgkin's lymphoma: different patterns in first-degree relatives

In order to evaluate the importance of genetic susceptibility in Hodgkin's disease (HD) and non-Hodgkin's lymphoma (NHL) we retrospectively analysed 31 families with lymphoma in first-degree relatives containing a total of 65 affected persons. We observed 20 HD/HD, 8 NHL/HD and 8 NHL/NHL pairs with median ages of diagnosis of 27, 36 and 48 years, respectively (p < 0.001). In HD/HD sib pairs were predominant in contrast to parent/child pairs in NHL/NHL (p = 0.04). There was a higher frequency of diseases with impaired immune function in NHL/NHL than in other pairs (p = 0.01). Comparison of ages and times of incidence of the pairs as well as sex-concordance rates are consistent with an age-specific genetic susceptibility to HD, but suggest a time-specific exposure in some NHL-prone families with or without compromised immune function.

The risk of malignant tumours in first-degree relatives of men with early onset prostate cancer: a population-based cohort study

Previous studies have indicated that hereditary prostate cancer is common among men with early onset prostate cancer. The aim of this study was to investigate the incidence of malignant tumours in first-degree relatives of men with early onset prostate cancer. All prostate cancer cases diagnosed before the age of 51 years from 1958 to 1994 were identified in the population-based Swedish Cancer Register. The first-degree relatives of clinical cases were identified through parish data. Their vital status and cancer incidence were studied in the Swedish Cancer Register, the Cause of Death Register and the Census Register. The expected incidence of malignant tumours for the first-degree relatives were calculated using regional cancer register data. Cause-specific standardised incidence ratios (SIR) and 95% confidence intervals (CI) were calculated. The study included 423 first-degree relatives of 89 men with clinical prostate cancer. The first-degree relatives' SIR for malignant tumours was 0.99 (95% CI 0.78-1.23). The SIR for prostate cancer diagnosed at any age was 1.43 (95% CI 0.82-2.33), and 3.37 for first-degree relatives diagnosed before the age of 70 years (95% CI 1.36-6.94). There was no significantly increased risk of any non-prostatic malignant tumour. Only in five of the families did the pedigree show a pattern of hereditary prostate cancer. The first-degree relatives of men with early onset prostate cancer had more than a 3-fold increase in the risk of developing prostate cancer before the age of 70 years, but their total cancer risk was not increased. This study does not support the assumption that dominantly inherited susceptibility is a major cause of early onset prostate cancer.

Familial nontoxic multinodular thyroid goiter locus maps to chromosome 14q but does not account for familial nonmedullary thyroid cancer

Thyroid goiter is a common condition that is often associated with iodine deficiency. Familial forms of goiter in areas not known to feature iodine deficiency are much less common. We have performed a genomic search on a single large Canadian family with 18 cases of nontoxic multinodular goiter in which 2 individuals also had papillary lesions highly suggestive of papillary carcinoma. A locus on chromosome 14q (MNG1 [multinodular goiter 1]) has been identified, with a maximal two-point LOD score of 3.8 at D14S1030 and a multipoint LOD score of 4.88 at the same marker, defined by D14S1062 (upper boundary) and D14S267 (lower boundary). The gene encoding thyroid-stimulating hormone receptor (TSHR), which is located on chromosome 14q, is outside the linked region. To determine the role of this gene in familial nonmedullary thyroid cancer (NMTC), we studied 37 smaller pedigrees each containing at least two cases of NMTC. Analysis by both parametric and nonparametric methods indicates that only a very small proportion of familial NMTC (point estimate 0.001, support intervals 0-.6 under a dominant model) is attributable to MNG1.

Family history facilitates the early diagnosis of prostate carcinoma

BACKGROUND

Although all men age >50 years are at an increased risk for the development of prostate carcinoma, 2 major factors increase this risk: family history and race. This article outlines the influence of family history on the risk of prostate carcinoma and current understanding of factors that increase this risk.

METHODS

Published studies investigating the familial and hereditary link to prostate carcinoma are reviewed. The results of an investigation into the mendelian inheritance of prostate carcinoma are discussed as well as the relation between hereditary cancer syndromes such as breast and ovarian carcinoma and prostate carcinoma.

RESULTS

A positive family history of prostate carcinoma increases the relative risk of prostate carcinoma in male first-degree relatives approximately twofold. Prostate carcinoma is inherited as an autosomal dominant trait. The relative risk of prostate carcinoma increases with multiple affected relatives.

CONCLUSIONS

Hereditary prostate carcinoma is estimated to be associated with 43% of men in whom the diagnosis of prostate carcinoma is made at age <55 years, 34% of men in whom the diagnosis is made at age <70 years, and only 9% of men diagnosed before age 85 years. Hereditary prostate carcinoma should be suspected in families with an early age at onset of the disease and/or multiple affected family members. Because hereditary prostate carcinoma is characterized by an early age at onset, first-degree relatives in high risk families should begin screening before age 50 years.

Family history of cancer and risk of breast cancer

The relationship between breast cancer risk and family history of cancer in first-degree relatives was investigated using data from a multicentric case-control study conducted in Italy between June 1991 and April 1994 on 2,569 women aged less than 75 years, with histologically confirmed incident breast cancer, and 2,588 control women admitted to hospital for acute, non-neoplastic, non-gynaecological conditions. Relative to women with no history, those with a family history of breast cancer had an odds ratio (OR) of 2.4 [95% confidence interval (CI) 1.9-3.0], and those with family history of intestinal cancer had an OR of 1.3 (95% CI 1.0-1.7). No significant relations emerged between breast cancer risk and family history of prostate (OR 1.1), ovarian (OR 1.3), cervical or endometrial (OR 1.2) or other cancers, except gallbladder (OR 8.6). The OR for family history of any type of cancer except breast cancer was 1.1. For family history of breast cancer the ORs were similar across strata of age of the proband, being 2.4 below age 45, 2.2 at age 45-59 and 2.7 above age 60, and whether the relative affected was the mother, sister(s) or both, while the risk appeared higher if the age at onset of breast cancer in the relative was lower than 40 years (OR 3.5), rather than higher (OR 2.2). Thus, our results, based on the investigation of all neoplasms in first-degree relatives, confirm that breast cancer risk is increased in women with a family history of breast cancer, while there was no material association with family history of cancer in general, excluding breast cancer.

Hematopoietic and lymphatic malignancies in vehicle mechanics

Although it is generally acknowledged that benzene causes leukemia, especially acute myeloid leukemia, considerable divergences persist in the assessment of the leukemia risk due to occupational low-level benzene exposure. Specifically, the risk for vehicle mechanics is considered by some authors as being nondetectable with epidemiologic methods, whereas others calculated that the incidence rate of leukemia (all types) in vehicle mechanics is increased more than 60 times. The purpose of this review is to examine the publications on this topic in light of criteria for causal inference and to discuss the possible role of bias, confounding factors, and chance. The results of this analysis reveal that there are surprisingly few epidemiologic observations supporting an increased incidence of leukemia in vehicle mechanics. Apparently, publications suggesting a leukemogenic effect of low-level benzene exposure in garage mechanics are more often quoted than their negative counterparts, although they are not better designed.

[Evaluation of cancer risk through genetic analysis?]

BACKGROUND

The recent literature of familial cancer, specifically related to germline mutations of RB1, p53, NF1, ATM, BRCA1, Mismatch repair genes and APC is reviewed.

RESULTS AND CONCLUSIONS

Germline mutations do not relate to an increased tumor risk of any single tissue, but instead to spectra of neoplastic diseases. The genetic background plays a major role in modifying the cancer risk. Therefore, mass screening for mutations of single genes seems to be without practical value. Only in combination with an adequate and informative family history can molecular genetic analysis significantly support the care for the individual. Comparison of the data of patients inheriting germline mutations and the experience from the corresponding "knockout" mouse demonstrate that only the p53 and APC knockout mice are useful models of human disease.

Molecular epidemiology of hematological neoplasms--present status and future directions

The field of molecular epidemiology, using modern epidemiological approaches and taking the advantage of the advances in molecular biology can provide new tools for the exploration of etiological determinants, either environmental or hereditary, in the development of hematological neoplasms. It is now possible to identify some host susceptibility characteristics, to measure the effective dose of exposure, and to identify early, pre-clinical biological effects, using sensitive and specific biomarkers. The significant variation in the incidence of hematological neoplasms in different geographical areas, races, and age groups, the high rates of familial aggregation in certain populations, the involvement of protooncogenes and tumor suppressor genes in the development of hematological neoplasms, as well as of many environmental agents such as chemicals, radiation, and viruses, support the important role of molecular epidemiology in the investigation of the development of hematological neoplasms.

Overview of the epidemiology of colorectal cancer

INTRODUCTION

The epidemiology of colorectal cancer has generated more interest recently, because recent developments in genetics, molecular biology, and genetic epidemiology have increased our understanding of the role of genes in the etiology of colorectal cancer. Interactions between genetic susceptibility and environmental factors in the etiology of cancer may be easier to define.

EPIDEMIOLOGY

Colorectal cancer is common in the Western world and is rare in developing countries. A sharp increase is seen in Eastern Europe and Japan.

ETIOLOGY

Molecular genetics has shown that accumulation of genetic changes is important in the development of colorectal cancer. Mutations in at least four to five genes are required for the formation of a malignant tumor. Environmental mutagenic factors may determine which susceptible individuals grow carcinomas. Environmental risk factors for colorectal cancer are found in a western diet, rich in fat, meat, and animal protein and low in fiber, fruit, and vegetables. The complex interrelations between food components make it difficult to define the precise role of specific food factors.

PREVENTION

Conclusive evidence of the effectiveness of primary prevention of colorectal cancer via dietary measures or nonsteroidal anti-inflammatory drugs is lacking. Secondary prevention by interrupting the adenoma carcinoma sequence is an actual possibility, its effectiveness, however, needs to be determined. Molecular genetics holds a promise for identifying populations at high risk for colorectal cancer, therefore, targeting the screening to make it more cost-effective.

Cancer in twins: genetic and nongenetic familial risk factors

BACKGROUND

Familial clustering has been observed for cancers that occur at specific sites. Most findings, which leave little doubt about the involvement of a heritable (i.e., genetic) component in the development of some cancers, are based on data from "cancer-prone" families or interviews with subjects who have cancer. The study of twins should be of value in cancer epidemiology because twins either are genetically identical or share half of their segregating genes.

PURPOSE

We linked the Swedish Twin Registry to the Swedish Cancer Registry, thereby identifying cases of cancer diagnosed from 1959 through 1992 in twins born in the period from 1886 through 1958, to assess the importance of both genetic and nongenetic (i.e., environmental) familial factors in determining cancer risk.

METHODS

Same-sex twin pairs with both individuals alive and living in Sweden in 1959-1961 or 1970-1972 were identified in the old cohort (born from 1886 through 1925) or the young cohort (born from 1926 through 1958), respectively, of the Swedish Twin Registry; pairs for whom zygosity (i.e., the number of eggs that gave rise to the twins) could be determined were considered further. The association of cancer with combined genetic and nongenetic familial factors was tested by comparing all twin pairs (regardless of zygosity) in which at least one member of the pair had been diagnosed with cancer at one of several specific sites with pairs in which neither twin had that cancer. Heritable effects alone were tested by comparing monozygotic (one egg) and dizygotic (two eggs) twin pairs. Statistical methods used in quantitative genetics and standard methods for epidemiologic research were used in parallel to analyze the data.

RESULTS AND CONCLUSIONS

In the 10503 twin pairs from the old cohort, 361.7 cases of malignant cancer were identified; 918 malignant cancers were identified in the 12883 twin pairs from the young cohort. When cancer sites with a total number of at least 200 cases and at least one twin pair concordant (i.e., both twins affected) for the site were evaluated, namely, cancers of the stomach, colon and rectum, lung, female breast, and prostate, as well as total cancer, profound genetic and/or nongenetic familial effects were identified in twins from the old cohort. Similar findings were obtained for twins in the young cohort for cancers of the prostate and female breast, as well as for total cancer. Genetic and nongenetic familial effects were also identified in twins from both cohorts for in situ cancer of the cervix. The increase in risk of colon and rectum, breast, cervical, and especially prostate cancer, but not stomach or lung cancer, tended to be greater if a monozygotic rather than a dizygotic twin were affected.

IMPLICATIONS

The identification of familial effects for total cancer in this study is consistent with the idea that individuals may possess a genetic susceptibility to cancer in general.

Parental cancer and risk of papillary and follicular thyroid carcinoma

In a population-based case-control study in the Uppsala-Orebro Health Care Region of Sweden, the histories of cancer among parents of 517 histologically confirmed cases of papillary and follicular carcinoma and of a similar number of sex- and age-matched controls were compared. The parental history of cancer was compiled through information from death certificates and from the nationwide Cancer Register. The incidence of malignancies in a cohort of parents of cases of thyroid cancer was also compared with the incidence in the whole Swedish population. A maternal history of cancer was more common among women with follicular carcinoma than among their controls (OR 2.11, 95% CI 0.96-4.67). Parents of probands with papillary carcinoma had an increased risk of thyroid cancer (OR 4.25, 95% CI 1.16-10.89), and mothers of probands with follicular carcinoma had an increased risk of stomach cancer (OR 3.65, 95% CI 0.99-9.35) compared with the general population. Cancer of the lung, breast, and pancreas were less common than in the general population. Familial cases of thyroid cancer were not limited to the papillary type. An inheritable pattern of carcinogenesis is possible for certain differentiated non-medullary thyroid cancers, but shared environmental exposures may also explain the parent-child associations of cancer in this study.

A segregation analysis of testicular cancer based on Norwegian and Swedish families

Clustering of testicular cancer cases in families is well known, although the aetiology is not. We present the results of a segregation analysis performed with the algorithm Pointer on familial data on 978 Scandinavian patients with testicular cancer. The segregation analysis favoured the involvement of major gene effects over models incorporating solely polygenic effects in testicular cancer aetiology. Overall, a recessive model best fits the family observations with an estimated gene frequency of 3.8% and a lifetime risk for homozygous men of developing the disease of 43%. This implies that 7.6% of men in the general population will be carriers of the mutant allele and that 0.1% would be homozygote and are, therefore, at high risk of developing the cancer. The testicular cancer incidence has changed greatly during the last generation. Also, the lethality of the disease has changed because of the introduction of new therapy. As failure to take account of such time trends might lead to inappropriate evidence for a recessive model, the analyses were repeated under different assumptions. The analyses favoured a recessive model of inheritance under all assumptions tested. However, the assumptions underlying the analyses are complex and, as this is the first segregation analysis of testicular cancer, the results must be interpreted cautiously.

No germline mutations in the dimerization domain of MXI1 in prostate cancer clusters. The CRC/BPG UK Familial Prostate Cancer Study Collaborators. Cancer Research Campaign/British Prostate Group

There is evidence that predisposition to cancer has a genetic component. Genetic models have suggested that there is at least one highly penetrant gene predisposing to this disease. The oncogene MXI1 on chromosome band 10q24-25 is mutated in a proportion of prostate tumours and loss of heterozygosity occurs at this site, suggesting the location of a tumour suppressor in this region. To investigate the possibility that MXI1 may be involved in inherited susceptibility to prostate cancer, we have sequenced the HLH and ZIP regions of the gene in 38 families with either three cases of prostate cancer or two affected siblings both diagnosed below the age of 67 years. These are the areas within which mutations have been described in some sporadic prostate cancers. No mutations were found in these two important coding regions and we therefore conclude that MXI1 does not make a major contribution to prostate cancer susceptibility.

Use of twins in search for tumor suppressor genes

A new approach is applied in the mapping of tumor suppressor genes: analysis of loss of heterozygosity (LOH) in concordant tumors of monozygotic and dizygotic twins. The method relies on recognition of genome locations undergoing loss in both twins in a high proportion of the set of all twin pairs examined. The method effectively pinpoints, and excludes, the loci of potential tumor suppressor genes. With the help of a high density linkage map any such candidates can be placed within a narrow region of a chromosome arm and perhaps matched with known genes. The analysis of the Swedish Twin Registry has shown a clear genetic component for breast cancer. We have identified mono- and dizygotic twins concordant for breast cancer and collected the pathology specimens. Tumor and normal tissue was microdissected and microsatellite analysis carried out to test for allelic loss (LOH) in entirely new and putative chromosomal loci in this cancer. It can be calculated that using only six pairs of informative monozygotic twins, a locus can be incriminated with a high probability. Using increasingly dense markers and search for homozygous deletions, it should be possible to map one or more candidates for breast cancer.

Familial aggregation of colorectal cancer in the general population

To investigate the familial aggregation of colorectal cancer in Denmark, parents and siblings of colorectal cancer patients diagnosed below age 60 years in the years 1982-1984 were identified through population registries. For 1,470 probands with families eligible for tracing, 1,376 mothers, 1,303 fathers and 3,259 siblings were identified. They contributed 222,634 person-years, and 325 cases of colorectal cancer were observed during the follow-up period 1943-1992. All data were retrieved from population registries and consequently were free from any reporting bias. The overall standardized morbidity ratio (SMR) compared with the Danish population was 2.02 (95% confidence interval [CI] 1.81-2.25), significantly different between the parents (1.78, 95% CI 1.55-2.04) and the siblings (2.65, 95% CI 2.21-3.17). A strong dependence on the proband's age at diagnosis was seen for the sibling risk; siblings of probands less than 50 years old at diagnosis had a 5-fold risk compared with the general population. This dependence was not seen for parents, but the risk tended to be higher for parents of younger ages. No other factor was seen to influence the relative risk. The observation of an 80% increased risk among the parents and a 170% increased risk among the siblings indicates that the genetic component is one source, but probably not the only one, of familial aggregation of colorectal cancer. The cost benefit of screening siblings of colorectal cancer patients is substantially higher than that for the total population.

Pancreatic adenocarcinoma: epidemiology and genetics

Pancreatic adenocarcinoma is an important cause of death from cancer throughout the developed world. There are few established environmental risk factors, but a previous history of pancreatitis and exposure to tobacco and salted food appear to be the most important. A family history of pancreatic adenocarcinoma is not common in patients with this disease, but recent research has shown that pancreatic adenocarcinoma can be a feature of cancer susceptibility syndromes associated with germline mutations in p16, BRCA1, BRCA2, and APC. This highlights the need for a full family history in apparently sporadic cases. Somatic mutations in p16, BRCA2, and APC have also been reported in pancreatic cancer; however, K-RAS mutations appear to be the commonest oncogenic alteration. Recent advances in our understanding of the basis of hereditary cancer syndromes may be applicable to the diagnosis, treatment, and possibly prevention of pancreatic adenocarcinoma in the future.

Some public health issues in the current state of genetic testing for breast cancer in Australia

Two genes associated with a high breast cancer risk (BRCA1 and BRCA2) have been discovered recently from study of large breast-cancer-dense kindreds. It is problematic to make inferences from these atypical families to the general population. Nevertheless, it appears that about 1 to 2 per cent of all breast cancer may be due to rare deleterious mutations in BRCA1 or BRCA2. The majority of breast cancer families with fewer than four cases are likely to have cancers not attributable to these genes. There may be more common mutations in other genes (such as ATM, HRAS1) that confer a moderate risk of breast cancer, and may account for 5 to 15 per cent of cases. At this early stage of cancer genetics, the risks associated with particular mutations are not known, there are no proven and acceptable strategies for women with an inherited susceptibility to ameliorate risk or improve prognosis, and risk estimates appropriate for Australian women with a family history of breast cancer are not established, although data from the United States may overestimate risk. Information is needed from population-based studies, such as the Australian Breast Cancer Family Study (Hopper et al. Breast 1994; 3: 79-86), but 100 per cent mutation detection in large cancer genes is difficult and expensive. Development of a systematic, research-oriented, evidence-based approach to genetic testing in Australia is recommended. Australia could lead the world in having common protocols used in breast cancer clinics across the country, linked to a national research consortium and database.

Familial risks of squamous cell carcinoma of the head and neck: retrospective case-control study

OBJECTIVE

To determine the contribution of inheritance to the incidence of squamous cell carcinoma of the head and neck.

DESIGN

Historical cohort study. First degree relatives of cases with squamous cell carcinoma of the head and neck made up the exposed cohort and first degree relatives of spouses of cases made up the comparison unexposed cohort.

SETTING

Ear, nose, and throat clinic in a large metropolitan teaching hospital.

SUBJECTS

1429 first degree relatives of 242 index cases of squamous cell carcinoma of the head and neck; as controls, 934 first degree relatives of the spouses of 156 index cases.

MAIN OUTCOME MEASURES

Relative risk of developing squamous cell carcinoma in first degree relatives of cases compared with risk in first degree relatives of spouses.

RESULTS

The adjusted relative risk for developing head and neck cancer if the index case had squamous cell carcinoma of the head and neck was 3.79 (95% confidence interval 1.11 to 13.0). There were no significantly increased risks associated with a family history of cancer at other sites. The adjusted relative risk for squamous cell carcinoma of the head and neck was 7.89 (1.50 to 41.6) in first degree relatives of patients with multiple primary head and neck tumours.

CONCLUSIONS

These data suggest that genetic factors are important in the aetiology of head and neck cancer, in particular for patients with multiple primary cancers. Given the prolonged exposure of these subjects to carcinogens, these genetic factors may have a role in modifying carcinogen activity or in host resistance to carcinogens. Inherited factors may be important in persons with environmentally induced cancers.

Increased incidence of cancer in first degree relatives of women with double primary carcinomas of the breast and colon

Breast and colon cancer are among the most common cancers in the developed world. Several epidemiological studies suggest that the occurrence of one of these two cancers in a woman may predispose to the development of the other. The occurrence of both forms of cancer in the same woman may be because of chance or common susceptibility. In order to determine how frequently double primary cancers have a hereditary basis, we conducted a registry based study at a single Montreal hospital. Cancer rates in first degree relatives of patients with multiple primaries were compared with provincial age standardised incidence rates and relative risks (RRs) were estimated. In first degree relatives under 45 there was a total of 15 cancers observed, compared with 3.70 expected, giving an RR of 4.05 (95% CI: 2.27-6.68). The RR for colon cancer was significantly increased among male relatives. For relatives less than 45 years old at diagnosis, the RR for colon cancer was 66.7 (95% CI: 13.8-195) (three cases observed, 0.045 expected). For all ages the RR was 5.02 (95% CI: 2.04-10.5). The RR for breast cancer was 5.92 (95% CI: 1.91-13.8) for female relatives under 45 (five cases observed, 0.845 expected) and 2.14 (95% CI: 1.07-3.83) for breast cancer at any age. These results suggest that there may be genes that predispose to both breast and colon cancer in certain people.

RET mutations in human disease

The RET proto-oncogene is at the origin of one of the most interesting models of human disease caused by mutations in a receptor tyrosine kinase gene. Somatic rearrangements of RET are involved in the aetiology of a variable proportion of papillary thyroid carcinomas (PTC), the most common type of thyroid tumour whose prevalence is increasing in areas heavily exposed to radioactive fallout after the Chernobyl accident of 1986. Moreover, germline RET mutations are associated with the three variants of the inherited cancer syndrome known as multiple endocrine neoplasia type 2 (MEN2A, MEN2B and FMTC). Finally, RET mutations or heterozygous deletions of the whole gene cause the autosomal dominant form of Hirschsprung disease (HSCR), a congenital disorder of the enteric nervous system (ENS).

Cancer mortality in relatives of women with breast cancer: the OPCS Study. Office of Population Censuses and Surveys

Mortality from cancer and other causes in male and female first-degree relatives of women with breast cancer diagnosed before age 60 has been examined in a large population-based cohort study, providing estimates of familial risks free from ascertainment or recall bias. Relatives of 3,295 patients with breast cancer diagnosed in the UK between 1954 and 1981 were identified through a register of households established in 1939. The 11,678 first-degree relatives thus identified were followed up through national records until the end of 1992. Over this period 5,421 deaths (including 1,527 cancer deaths) occurred in these relatives. Mortality from breast cancer was significantly raised in first-degree relatives (SMR 187, 248 deaths), and there was also significant excess mortality from cancers of the larynx (SMR 177, 17 deaths), endometrium (SMR 166, 29 deaths) and unspecified neoplasms (SMR 153, 70 deaths). The SMR for ovarian cancer was 130, based on 58 deaths (p = 0.06). There was no marked excess for other sites or for non-neoplastic causes of death, but there was a significant deficit in mortality from cervical cancer (SMR 63, 18 deaths). The SMR for breast cancer increased significantly with decreasing age of the relative. After allowing for age, sisters of cases had a slightly (though non-significantly) higher risk than mothers (ratio of SMRs 1.22). These results, together with penetrance estimates from linked families, suggest that approximately one woman in 800 carries BRCAI, the susceptibility gene on chromosome 17q, and that this gene causes about 1% of all breast cancers.

Cancer mortality in relatives of women with ovarian cancer: the OPCS Study. Office of Population Censuses and Surveys

Mortality from cancer and other causes in first-degree relatives of women with ovarian cancer diagnosed before age 60 has been examined in a large population-based cohort study in England and Wales. Relatives of 1,188 ovarian-cancer cases diagnosed between 1954 and 1981 were identified through a register of households established in 1939. Some 4,111 first-degree relatives living in the same household and having the same surname as the index case were followed up through national records until the end of 1992. Over this period, 1,950 deaths (including 574 cancer deaths) occurred in the relatives. Mortality rates within the cohort were compared with age-, sex- and period-adjusted mortality rates for England and Wales. Mortality from ovarian cancer in first-degree relatives was significantly raised (SMR 223, 95% CI 155-310) although the excess was smaller than that found in case-control studies. The SMR increased with decreasing age of the relative, though not with decreasing age of the index case. After allowing for age, sisters of cases had higher ovarian-cancer mortality than mothers (sister:mother SMR ratio 1.89, p = 0.06). The SMR was greater in individuals having 2 first-degree relatives with ovarian cancer (4 deaths versus 0.17 expected, SMR 242). Relatives of ovarian cancer cases also had significantly increased mortality from cancers of the stomach (SMR 146, 69 deaths) and rectum (SMR 150, 33 deaths), and increased mortality from colon cancer, breast cancer and pancreatic cancer which failed to reach statistical significance. Individuals having a relative with colorectal cancer and a relative with ovarian cancer showed a high mortality from both cancers (11 colorectal-cancer deaths versus 1.23 expected, 4 ovarian-cancer deaths versus 0.66 expected.

Familial prostate cancer in Sweden. A nationwide register cohort study

BACKGROUND

Although prostate carcinoma is not widely recognized as a familial cancer, familial aggregation of this disease has been shown in some retrospective case-control studies. To study familial prostate cancer in Sweden, a population-based cohort study was performed, that attempted to avoid possible bias connected with some earlier studies of familial prostate cancer.

METHODS

A nationwide register cohort study was conducted using an unselected study population. The study cohort of 5496 sons of Swedish men found to have prostate cancer between 1959 and 1963 was identified through parish offices. All prostate cancer patients reported between 1958 and 1990 in this cohort were identified through linkage to the Swedish Cancer Register. The expected number of prostate cancer patients was calculated using incidence rates obtained from the same register.

RESULTS

A highly significant increased overall standardized incidence ratio (SIR) of 1.70 (95% confidence interval, 1.51-1.90) was obtained for prostate cancer in this cohort, with 302 observed cases compared with 178 expected prostate cancers. The SIR was 3.38 among patients aged 45-49 years at diagnosis, with the risk gradually decreasing to a SIR of 1.35 among patients older than 80 years (trend, P = 0.013). Among sons with a father whose prostate cancer was diagnosed at an early age (< 70 years), a significant trend (P = 0.01) for prostate cancer risk was observed due to early onset of the disease.

CONCLUSIONS

This cohort study provides further evidence that a positive family history of prostate cancer is a risk factor for developing the disease in an unselected population. The increased risk was found for all ages, but was more pronounced in younger men.

The genetics of breast and ovarian cancer

A number of genes are known to be involved in inherited susceptibility to breast and/or ovarian cancer. In the context of high-risk families the most important genes are BRCA1 on chromosome 17q, which is associated with a high penetrance of both breast and ovarian cancer, and BRCA2 on chromosome 13q, which causes a high risk of breast cancer but a lower risk of ovarian cancer. Other high-risk cancer genes that confer increased risks of breast or ovarian cancer in addition to other cancers include the hereditary non-polyposis colorectal cancer genes and the TP53 gene, which causes breast cancer as part of the Li-Fraumeni syndrome. The predisposing mutations in these genes are relatively rare in the population. More common genes which are associated with an increased, but lower, risk of breast cancer are the ataxiatelangiectasia gene and the HRAS1 gene. This paper reviews recent progress in mapping and cloning of these susceptibility genes, and provides estimates of the cancer risks associated with each gene and the frequency of predisposing mutations.