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

The effect of a single BRCA2 mutation on cancer in Iceland

OBJECTIVE

To estimate the risk of malignant diseases in families of probands with the same mutation in the BRCA2 gene.

DESIGN

A cohort study using record linkage of a breast cancer family resource and the Icelandic Cancer Registry.

SETTING

Iceland.

SUBJECTS

Families of 995 breast cancer patients, from which 887 were tested for a single founder 999del5 mutation; 90 had the mutation and 797 did not.

RESULTS

Relatives of probands with the mutation had significantly increased relative risk (RR) of breast cancer. For first degree relatives, the RR was 7.55 (95% CI 6.04 to 9.03) but was 1.72 (95% CI 1.49 to 1.96) in first degree relatives of probands without the mutation. For prostate and ovarian cancer, the first and second degree relatives of probands with the mutation had a significantly increased RR, but in families of probands without the mutation no significant familial risk was found.

CONCLUSIONS

The 999del5 mutation in the BRCA2 gene explains a substantial proportion of familial risk of breast cancer in Iceland, but significant familial risk remains in relatives of probands without the mutation. For prostate and ovarian cancer, the mutation accounts for most of the familiality observed in families of breast cancer patients.

Analysis of the RNASEL gene in familial and sporadic prostate cancer

The RNASEL gene on chromosome 1q25 was recently identified as a candidate gene for hereditary prostate cancer (PC). To confirm these findings, we screened 326 patients from 163 families with familial PC for potential germline mutations, by use of conformation-sensitive gel electrophoresis, followed by direct sequence analysis. A total of six variants were identified, including one intronic and five exonic changes (three missense and two silent alterations). There were no unequivocal pathogenic changes. To further test for potential associations between genes and increased risk for disease, the three missense polymorphisms (Ile97Leu, Arg462Gln, and Glu541Asp) were genotyped in 438 patients with familial PC and in 510 population-based control subjects. Association testing revealed no significant differences between patients and control subjects for either the Leu97 variant (chi(2) trend test = 1.42; P=.23) or the Asp541 variant (chi2=1.52; P=.22). However, significant differences were detected for the Arg462Gln genotypes (chi2=5.20; P=.02; odds ratio [OR] = 0.54; 95% confidence interval [CI] 0.32-0.91) when the genotype Gln/Gln was compared with Arg/Arg. In subset analyses, associations were also observed in the younger group (age at diagnosis </=64 years) (P=.0008; OR=0.29; 95% CI = 0.13-0.66), in node-negative patients (P=.01; OR=0.48; 95% CI 0.27-0.84), patients with stage T(1)/T(2) disease (P=.008; OR=0.39; 95% CI 0.2-0.75), and patients with low-grade disease (P=.01; OR=0.40; 95% CI 0.20-0.78). To evaluate whether this variant was also associated with sporadic PC, we genotyped an additional 499 patients with sporadic PC. Differences in frequency were not detected between patients with sporadic disease and control subjects. However, the same association was observed between patients with familial disease and patients with sporadic disease for the entire group (chi2=4.82; P=.03), as well as in the subset analyses. These results suggest that polymorphic changes within the RNASEL gene may be associated with increased risk of familial but not sporadic PC.

Cancer risks among long-standing spouses

We estimated risks for concordant and discordant cancers in spouses in order to quantify cancer risks from the shared environment. The study was restricted to spouses who had one or more children in common and who lived together for at least 15 years after the first child's birth. The nation-wide Family-Cancer Database was used as the source of family and cancer data. Standardised incidence ratios were calculated for concordant and discordant cancers in spouses after 50 years of age. Among the 18 cancer sites considered, only three sites, stomach, lung and bladder, showed concordant increases of cancer among spouses, standardised incidence ratios ranging only from 1.19 to 1.38. Additionally, gastric and pancreatic cancer were associated among spouses, as did many cancers which were related to tobacco smoking or human papilloma virus infection. By contrast, standardised incidence ratios of colon, rectal, renal and skin cancers showed no increases among spouses. Shared lifestyle among family members seems to explain only a small proportion of familial cancer susceptibility. Because lifestyles are likely to differ more between parents and offspring than between spouses, familial cancer risks between parents and offspring are even more likely to be due to heritable than environmental effects.

Family history and prostate cancer screening with prostate-specific antigen

PURPOSE

Early detection of prostate cancer has been recommended for men with affected first-degree relatives despite the lack of evidence for mortality reduction. We therefore evaluated the impact of family history in the Finnish prostate cancer screening trial.

PATIENTS AND METHODS

Approximately 80,000 men were identified from the population register for the first screening round. Of the 32,000 men randomized to the screening arm, 30,403 were eligible at the time of invitation. A blood sample was drawn from the participants (n = 20,716), and serum prostate-specific antigen (PSA) was determined. Men with a PSA level > or = 4.0 ng/mL were referred for prostate biopsy. Information on family history was obtained through a self-administered questionnaire at baseline.

RESULTS

A total of 964 (5%) of the 20,716 screening participants had a positive family history, and 105 (11%) were screening-positive. Twenty-nine tumors were diagnosed, corresponding to a detection rate of 3.0% (29 of 964) and a positive predictive value of 28% (29 of 105). Of the 19,347 men without a family history, 1,487 (8%) had a PSA level > or = 4.0 ng/mL. The detection rate was 2.4% (462 of 19,347) and the positive predictive value was 31% (462 of 1,487). The risk associated with a positive family history was not substantially increased (rate ratio, 1.3; 95% confidence interval, 0.9 to 1.8). The results were not affected by the age of the screenee or age at diagnosis of the affected relative. The program sensitivity was 6% (29 of 491) (ie, selective screening policy would have missed 94% of cancers in the population). No differences were seen in the characteristics of screen-detected cancers by family history.

CONCLUSION

Our findings provide no support for selective screening among men with affected relatives.

Genetic susceptibility to chronic lymphocytic leukemia

There is increasing evidence that a subset of chronic lymphocytic leukemia is caused by an inherited predisposition. Here we review the evidence for an inherited predisposition, the characteristics of familial cases and evidence for the involvement of specific genes.

Environmental and heritable causes of cancer among 9.6 million individuals in the Swedish Family-Cancer Database

The genetic and environmental components in 15 common cancers were estimated using the nationwide Swedish Family-Cancer Database. Tetrachoric correlations were used to describe similarity in cancer liability among family members. Structural equation modeling was used to derive estimates of the importance of genetic and environmental effects. Statistically significant estimates of proportion of cancer susceptibility, accounted for by genetic effects, were obtained for all studied cancers except for leukemia. The estimate was highest in thyroid cancer (53%), followed by tumors at endocrine glands (28%), testis (25%), breast (25%), cervix (22%), melanoma (21%), colon (13%), nervous system (12%), rectum (12%), non-Hodgkin lymphoma (10%), lung (8%), kidney (8%), urinary bladder (7%), stomach (1%) and leukemia (1%). The estimates of shared environmental effects ranged from 0% (cervix) to 15% (stomach). The childhood shared environmental effects were most important in testicular cancer (17%), stomach cancer (13%) and cervix in situ (13%). Our results indicate that environment has a principal causative role in cancer at all studied sites except for thyroid. The relatively large effect of heritability in cancer at some sites, on the other hand, indicates that even though susceptibility genes have been described at many cancer sites, they are likely to explain only part of the genetic effects.

Kidney cancer in the Swedish Family Cancer Database: familial risks and second primary malignancies

BACKGROUND

Familial risks in kidney cancer and association with second primary malignancies were studied using the nationwide Swedish Family Cancer Database.

METHODS

Cancer data were retrieved from the Swedish Cancer Registry from years 1961 to 1998 and included 23,137 cases of kidney cancer. Standardized incidence ratios (SIRs) were used to measure the cancer risks.

RESULTS

Seventy-one families were identified where both a parent and an offspring had kidney cancer, giving a familial risk for offspring of 1.56 (1.22 to 1.95) and population attributable proportion of 0.78%. A risk for kidney cancer from an affected sibling was considerably higher with a SIR of 4.72 (2.28 to 9.20), giving an attributable proportion of 0.77%. The discordant tumor site that was associated with kidney cancer between two generations was hemangioblastoma of central nervous system. Discordant cancer sites that were associated with kidney cancer in siblings were ovaries, endocrine glands and pancreas. There was an over threefold increase of second primary malignancies of the urinary bladder, nervous system and endocrine gland in kidney cancer patients. The risks for second primary hemangioblastoma following kidney cancer or familial kidney cancer was 21.19 (6.69 to 43.83) and 1206 (114 to 3456), respectively.

CONCLUSIONS

The high ratio of sibling risk to offspring risk in kidney cancer may reflect a recessive susceptibility. The high risk for second primary cancers in the patients without family history is consistent with a polygenic model and variable degree of environmental modification.

Genetic susceptibility--molecular epidemiology of head and neck cancer

In parts of the developing world (South Central Asia in particular), squamous cell carcinoma of the head and neck (SCCHN) is one of the most common malignancies encountered. Although tobacco and alcohol are clearly defined as etiologic factors in these malignancies, clinical observations have suggested that inherited genetic factors put some individuals at increased risk for SCCHN. Emerging data (both phenotypic and genotypic) support this concept of genetic susceptibility to SCCHN and point to differences in DNA repair ability, carcinogen metabolism, and cell cycle control as the systems important to the risk of tobacco-induced malignancies. The ability to identify such high-risk individuals will have major influences on the practice of cancer prevention in the future.

Risk assessment & genetic testing

Ovarian cancer is the fifth most common cause of cancer death in women in Western countries and family history is one of the strongest known risk factors. Approximately 5 to 13% of all ovarian cancer cases are caused by the inheritance of cancer predisposing genes with an autosomal pattern of transmission. The inherited fraction of ovarian cancer may differ between populations. Based on analysis of familial ovarian cancer pedigrees and other epidemiological studies, three hereditary ovarian cancer syndromes have been defined. The identification of the genes responsible for most hereditary ovarian cancers has open a new area of early detection methods and preventive procedures specifically dedicated to women identified as carrying ovarian cancer predisposing genes. Predictive oncology is best performed by a dedicated unit with professionals aware of all the issues surrounding genetic testing.

Familial and second gastric carcinomas: a nationwide epidemiologic study from Sweden

BACKGROUND

Familial risks in gastric carcinoma have been assessed mainly through case-control studies based on reported but not medically verified carcinomas in family members. Reliable data on familial risks are needed for prevention and clinical decisions.

METHODS

The authors used the nationwide Swedish Family-Cancer Database on 10.2 million individuals and more than 34,000 gastric carcinomas to calculate standardized incidence ratios (SIRs) and 95% confidence intervals (CIs) for gastric carcinoma in offspring, from birth to 66 years old, by carcinomas in family members. In addition, SIRs for second gastric carcinomas were analyzed.

RESULTS

Standardized incidence ratios for gastric carcinoma were 1.31 (95% CI, 0.97-1.70) and 1.47 (95% CI, 1.08-1.92) when a parent presented with gastric carcinoma or gastric adenocarcinoma, respectively. The risk was 1.59 (95% CI, 1.10-2.16) in offspring whose diagnosis was at ages older than 50 years. Offspring risk from parental corpus carcinoma was of borderline significance whereas that from cardia carcinoma was below unity. The sibling risk for gastric carcinoma was 3.16 (95% CI, 1.35-5.72) and 5.75 (95% CI, 2.07-11.26) when diagnosed before age 50. The population attributable proportion of familial gastric carcinoma was 0.45%. Risks for second gastric carcinomas were increased in men and women after esophageal and skin carcinomas, and after non-Hodgkin lymphoma.

CONCLUSIONS

The data suggest that environmental factors, perhaps Helicobacter pylori infections are the main reason for familial clustering of gastric carcinoma. The population attributable proportion of familial gastric carcinoma is much lower than that cited in the literature. The patterns of multiple carcinomas suggest that immunologic factors modulate susceptibility to gastric carcinoma.

Bone tumorigenesis induced by alpha-particle radiation: mapping of genetic loci influencing predisposition in mice

The present study was carried out to determine the extent to which genetic factors modify the incidence of radiation-induced bone tumorigenesis in mice, and to map putative susceptibility genes. We conducted a genome-wide linkage analysis in a cohort of 47 interstrain backcrossed mice. After the mice were injected with the bone-seeking alpha-particle-emitting radionuclide (227)Th, 21 of the mice developed osteosarcomas. Two loci, one on chromosome 7 close to D7Mit145 and a second on chromosome 14 (D14Mit125), exhibited suggestive linkage to osteosarcoma predisposition, with LOD scores of 1.37 and 1.05, respectively. The LOD score increased considerably when interaction between these two loci was taken into account (LOD = 3.48). Nine of 12 mice inheriting a susceptibility allele at both loci developed osteosarcomas after (227)Th injection, compared to only four osteosarcomas in 18 animals that did not inherit either of the susceptibility alleles. Variance component analysis revealed that these genetic factors determine approximately one-fifth of the total incidence of osteosarcomas. This study demonstrates the presence of a genetic component that modulates predisposition to radiation-induced osteosarcoma.

Specific haplotypes of the RET proto-oncogene are over-represented in patients with sporadic papillary thyroid carcinoma

BACKGROUND

Papillary thyroid carcinoma (PTC), which may be sporadic (95%) or familial (5%), has a prevalence adjusted for age in the general population of 1:100 000. Somatic rearrangements of the RET proto-oncogene are present in up to 66% of sporadic tumours, while they are rarely found in familial cases.

PURPOSE

In order to determine if some variants of this gene, or a combination of them, might predispose to PTC, we looked for an association of RET haplotype(s) in PTC cases and in controls from four countries matched for sex, age, and population.

METHODS

Four single nucleotide polymorphisms (SNPs) across the RET coding sequence were typed and haplotype frequencies were estimated. Genotype and haplotype distributions were compared among these cases and controls.

RESULTS

Ten haplotypes were observed, the seven most frequent of which have been previously described in sporadic Hirschsprung patients and controls. The single locus analyses suggested association of exon 2 and exon 13 SNPs with sporadic PTC. The haplotype analysis showed over-representation of one haplotype in French and Italian sporadic PTC, whereas a different haplotype was significantly under-represented in French familial PTC.

CONCLUSIONS

Our data suggest that some variants of RET and some specific haplotypes may act as low penetrance alleles in the predisposition to PTC.

Hereditary diffuse gastric cancer

Hereditary diffuse gastric cancer (HDGC) is a cancer predisposition syndrome caused by germline mutation of the gene for the cell-to-cell adhesion protein E-cadherin. The syndrome is dominated by predisposition to the histologically diffuse, poorly differentiated form of gastric cancer. It is not associated with intestinal-type gastric cancer, but families may have an elevated risk of lobular breast cancer. Here, we review the identified families, mutations, and proposed mechanisms by which E-cadherin loss promotes tumorigenesis.

Familial aggregation of urothelial cell carcinoma

Urothelial cell carcinoma (UCC) is not considered to be a familial disease. Familial clustering of UCC was described in several case reports, however, some with an extremely early age at onset suggesting a genetic component. Epidemiological studies yielded inconsistent evidence of familial UCC, possibly because of low power and the inability to adjust for strong confounding. In our study the existence of a familial subtype of UCC was evaluated, as well as familial clustering of UCC with other types of cancer. A population-based family case-control study was performed including patients newly diagnosed with UCC of the bladder, ureter, renal pelvis or urethra, between January 1995 and December 1997, in the southeastern part of the Netherlands. Information on the patients' first-degree relatives was collected by postal questionnaire and subsequent telephone calls. The patients' partners filled out a similar questionnaire on their relatives. All reported occurrences of UCC were verified using medical records. Disease occurrence among case-relatives and control-relatives was compared to obtain the familial risk. Random effect proportional hazards regression analyses were used to calculate this familial risk while adjusting for age, gender and smoking behavior. In 95 families of the 1,193 patients and in 36 families of the 853 partners at least 1 relative was diagnosed with UCC. This yielded an adjusted hazard ratio (HR) of 1.8 (95% CI: 1.3-2.7). An increased risk was also found for cancer of the hematolymphopoietic system (hazard ration = 1.9, 95% CI: 1.2-3.1) among case-relatives. These results indicate that UCC has a familial component with an almost 2-fold increased risk among first-degree relatives of patients with UCC, which cannot be explained by smoking. Future segregation analyses may indicate whether this clustering can be attributed to genetic susceptibility.

Familial cancer aggregation and the risk of lung cancer

CONTEXT

Around 90% of lung cancer worldwide is attributable to cigarette smoking, although less than 20% of cigarette smokers develop lung cancer. Other factors such as diet, chronic lung diseases, occupation and possibly environmental agents also contribute to this cancer. Genetic factors seem to play a role in lung cancer, but the precise characteristics influencing lung cancer susceptibility are not known, since genetic factors are easily obscured by the strong environmental determinants of lung cancer, particularly smoking.

OBJECTIVE

To estimate the effect that cancer occurrence among first-degree relatives has on the risk of lung cancer.

DESIGN

Hospital-based case-control study.

SETTING

The metropolitan region of São Paulo, Brazil.

PARTICIPANTS

334 incident lung cancer cases and 578 controls matched by hospitals.

MAIN MEASUREMENTS

By means of a structured questionnaire, cases and controls were interviewed about cancer occurrence in first-degree relatives, tobacco smoking, exposure to passive smoking, occupation, migration and socioeconomic status. Non-conditional logistic regression was used to calculate the risk of familial cancer aggregation, the effect of cancer in first-degree relatives and smoking in conjunction, and for controlling confounders.

RESULTS

The adjusted odds ratio (OR) revealed a slight, but not statistically significant, excess risk of lung cancer for subjects with a history of lung cancer in relatives (OR 1.21; 95% confidence interval [CI] 0.50 - 2.92). The same was found among those with a history of other tobacco-related cancers in relatives (OR 1.36; 95% CI 0.87 - 2.14). A step gradient effect was observed regarding lung cancer risk, in accordance with increases in the number of pack-years of cigarette consumption. An interaction between familial cancer aggregation and tobacco smoking was detected.

CONCLUSIONS

A mildly elevated risk of lung cancer among persons with a positive history of lung and other tobacco-related cancers was observed. The finding of an interaction between the variables of familial cancer aggregation and smoking suggests that familial cancer aggregation could be considered as a marker of susceptibility, increasing the risk of lung cancer among smokers. These results improve our knowledge of lung carcinogenesis and can guide future cancer genetic studies.

Family history and the risk of stomach cancer death in Japan: differences by age and gender

Familial aggregation of stomach cancer has long been observed. The effect on disease risk of family history and its magnitude according to the type of affected relatives, however, is not well known. We conducted a prospective analysis using the JACC study (Japan Collaborative Cohort Study For Evaluation of Cancer Risk, sponsored by Monbusho) data. During the follow-up period, 662 stomach cancer deaths were documented. A positive history of stomach cancer in one or more first-degree relatives was associated with a significantly increased risk of death from the disease in both men (RR 1.60; 95% CI 1.11-2.31) and women (RR 2.47; 95% CI 1.50-4.06). In the subanalysis stratified by age, the association between positive family history and stomach cancer was stronger in the age group from 40-59 (RR 2.62; 95% CI 1.34-5.11 for men and RR 5.88; 95% CI 2.70-12.82 for women) than in the age group from 60-79 (RR 1.31; 95% CI 0.84-2.05 for men and RR 1.44; 95% CI 0.72-2.88 for women). In the age group from 40-59, men with father's history and women with mother's and sister's history of the disease had a significantly increased risk (RR 3.14; 95% CI 1.51-6.55, RR 10.46; 95% CI 4.54-24.12, RR 13.39; 95% CI 3.89-46.12, respectively). When 2 or more family members were affected, the increment in the risk was prominent especially in women (RR 9.45; 95% CI 4.46-20.05). These results suggest the existence of a certain subtype of stomach cancer that is inherited more often by women from one generation to the next in gender-influenced fashion. Any preventive strategy should take into account the degree of individual susceptibility.

Population aspects of cancer genetics

A number of relatively rare, high-risk genes have been identified which predispose to common cancers such as breast, colon, and melanoma. Although these are clearly important in the clinical setting, it is also relevant to discuss the impact of these genes at the population level and to contrast these with that which could be ascribed to more common genetic variants which only confer a modest increased risk of cancer. In this review, we examine inferences about the role of genetics in cancer from ecological studies of incidence patterns from a number of population-based studies of familial and attributable risk. The relationship between the genetic model (genotypic risk, allele frequency, mode of inheritance) and the expected impact in the population in terms of both attributable risk and familial risk is presented. The advantages and limitations of using cancer occurrence in twins to measure the genetic contribution to specific cancer sites is discussed. The potential role of lower-penetrance genes in the overall cancer burden may be significant but may pose significant problems in the public health arena.

BRCA1 and BRCA2 mutations in a population-based study of male breast cancer

BACKGROUND

The contribution of BRCA1 and BRCA2 to the incidence of male breast cancer (MBC) in the United Kingdom is not known, and the importance of these genes in the increased risk of female breast cancer associated with a family history of breast cancer in a male first-degree relative is unclear.

METHODS

We have carried out a population-based study of 94 MBC cases collected in the UK. We screened genomic DNA for mutations in BRCA1 and BRCA2 and used family history data from these cases to calculate the risk of breast cancer to female relatives of MBC cases. We also estimated the contribution of BRCA1 and BRCA2 to this risk.

RESULTS

Nineteen cases (20%) reported a first-degree relative with breast cancer, of whom seven also had an affected second-degree relative. The breast cancer risk in female first-degree relatives was 2.4 times (95% confidence interval [CI] = 1.4-4.0) the risk in the general population. No BRCA1 mutation carriers were identified and five cases were found to carry a mutation in BRCA2. Allowing for a mutation detection sensitivity frequency of 70%, the carrier frequency for BRCA2 mutations was 8% (95% CI = 3-19). All the mutation carriers had a family history of breast, ovarian, prostate or pancreatic cancer. However, BRCA2 accounted for only 15% of the excess familial risk of breast cancer in female first-degree relatives.

CONCLUSION

These data suggest that other genes that confer an increased risk for both female and male breast cancer have yet to be found.

Gene expression in papillary thyroid carcinoma reveals highly consistent profiles

Papillary thyroid carcinoma (PTC) is clinically heterogeneous. Apart from an association with ionizing radiation, the etiology and molecular biology of PTC is poorly understood. We used oligo-based DNA arrays to study the expression profiles of eight matched pairs of normal thyroid and PTC tissues. Additional PTC tumors and other tissues were studied by reverse transcriptase-PCR and immunohistochemistry. The PTCs showed concordant expression of many genes and distinct clustered profiles. Genes with increased expression in PTC included many encoding adhesion and extracellular matrix proteins. Expression was increased in 8/8 tumors for 24 genes and in 7/8 tumors for 22 genes. Among these genes were several previously known to be overexpressed in PTC, such as MET, LGALS3, KRT19, DPP4, MDK, TIMP1, and FN1. The numerous additional genes include CITED1, CHI3L1, ODZ1, N33, SFTPB, and SCEL. Reverse transcriptase-PCR showed high expression of CITED1, CHI3L1, ODZ1, and SCEL in 6/6 additional PTCs. Immunohistochemical analysis detected CITED1 and SFTPB in 49/52 and 39/52 PTCs, respectively, but not in follicular thyroid carcinoma and normal thyroid tissue. Genes underexpressed in PTC included tumor suppressors, thyroid function-related proteins, and fatty acid binding proteins. Expression was decreased in 7/8 tumors for eight genes and decreased in 6/8 tumors for 19 genes. We conclude that, despite its clinical heterogeneity, PTC is characterized by consistent and specific molecular changes. These findings reveal clues to the molecular pathways involved in PTC and may provide biomarkers for clinical use.

Association of codon 72 polymorphism of p53 with lower prostate cancer risk

BACKGROUND

A common germline polymorphism of p53 produces a protein with an Arg to Pro change at codon 72. This Pro variant has altered biochemical properties suggesting altered cancer susceptibility.

METHODS

A case control study with 115 men with prostate cancer and 181 community control male subjects was conducted. Demographics, family history of cancer, and blood were obtained. Codon 72 genotypes were determined using PCR.

RESULTS

The Pro/Pro genotype was associated with a markedly lower risk of prostate cancer (OR = 0.23, CI = 0.07-0.79, P = 0.012). Similar reduction in risk was observed when the analysis was limited to Caucasian subjects (86% of total). Reduction in risk remained significant in a logistic regression model after correcting for age and family history of prostate cancer (OR = 0.14, CI = 0.03-0.71, P = 0.017).

CONCLUSIONS

Men with the p53 codon 72 Pro/Pro genotype appear to be at reduced risk of prostate cancer.

Differentiated thyroid carcinoma: a polygenic disease

Differentiated thyroid cancer is a rare disease and until recently was considered to be sporadic. However, increasing evidence has been found for a genetic basis of this disease. In approximately 5% of patients the differentiated thyroid cancer is dominantly inherited. Several families with different syndromes, of which differentiated thyroid cancer is a feature, have already been described. However, until now, single genes explain only a minority of cases. We hypothesize that differentiated thyroid cancer is a polygenic disease. Data from epidemiologic studies, about occult and multifocal carcinomas and the different response to specific risk factors contribute to this hypothesis.

Familial colorectal adenocarcinoma from the Swedish Family-Cancer Database

Familial risks for colorectal (CRC) adenocarcinoma were characterized from the Swedish Family-Cancer Database covering 9.6 million individuals, whose family relationships and cancers were obtained from registered sources, not sensitive to reporting or ascertainment bias. Cancer cases were retrieved from the Swedish Cancer Registry from years 1958-96. Standardized incidence ratios (SIRs) were calculated based on gender-, age-, period- and tumor type specific rates. A total of 4,794 and 67,925 CRCs were recorded in offspring and parents, respectively. For colon and rectal adenocarcinoma, the SIRs in offspring were 2.28 and 1.68 by parental CRC adenocarcinoma, giving attributable proportions of 6.45 and 3.31%, respectively. The SIR of CRC was over 10 when both offspring and parents were diagnosed at a young age. The risk for parental CRC adenocarcinoma was over 100 when 2 or more children were affected. The risk in siblings was also very high when a parent was affected. The familial cancer sites that associated with CRC were those typical of hereditary nonpolyposis colorectal cancer (HNPCC). This is the largest study published on familial CRC and the only one reporting specifically on adenocarcinoma. The data suggest that HNPCC is the largest single disease entity among CRCs, probably accounting for less than 50% of familial CRC. Other familial components appear heterogeneous, characterized by incomplete penetrance, recessive mode of inheritance and few associated tumor sites.

Analysis of hereditary component of cancer by use of a familial index by site

To quantify hereditary factors in the risk of cancer, we matched 1283047 cancer patients listed in the Swedish Cancer Registry with healthy controls from a national database, and identified the number of individuals who were first-degree relatives of other individuals in the same cohort. Division of the number of relatives in the patient cohort by the number in the control cohort yielded a "familial index". The following cancers had high familial indices: eye 16.5 (95% CI 2.5-666), testis 9.0 (3.2-35), Hodgkin's disease 6.5 (2.3-26.0), and thyroid 6.2 (3.7-12). Overall, however, familial factors made only a minor contribution to susceptibility to cancer.

Epidemiology of prostatic cancer in East Asia

Prostate cancer has become one of the most common malignancies in the world. The incidence of prostate cancer has rapidly increasing over the last decade in East Asia. In Japan, age-adjusted death rates due to prostate cancer rose from 4.4 to 8.6 per 100,000 between 1980 and 1998. Recent research has focused on age, race-related differences, patterns of familial aggregation, genetic factors, hormones, and diet. Epidemiological approach has identified several possible risk factors that may be useful for the prevention of prostate cancer and targeting high-risk individuals for early detection.

Increased risk for nonmedullary thyroid cancer in the first degree relatives of prevalent cases of nonmedullary thyroid cancer: a hospital-based study

The genetic basis for nonmedullary forms of thyroid cancer (NMTC) is less well established than that of medullary thyroid cancer. However, epidemiological and family studies suggest that a proportion of NMTC may be due to inherited predisposition. To estimate the familial risk of thyroid cancer, we conducted a hospital-based case-control study at the Princess Margaret Hospital in Toronto, Ontario, Canada, and at 2 university hospitals in Montréal, Québec, Canada. We obtained pedigrees from 339 unselected patients diagnosed with NMTC and from 319 unaffected ethnically matched controls. Family histories of cancer were obtained from the cases and controls for 3292 first degree relatives of cases and controls. Seventeen cases (5.0%) and 2 controls (0.6%) reported at least one first degree relative with thyroid cancer. In relatives of patients with thyroid cancer, the incidence of any type of cancer (including NMTC) was 38% higher than in relatives of controls (incidence rate ratio, 1.4; 95% confidence interval, 1.1-1.7). The relative risk for thyroid cancer was 10-fold higher in relatives of cancer patients than in controls (incidence rate ratio, 10.3; 95% confidence interval, 2.2-47.6). Our findings suggest that hereditary or other familial factors are important in a small proportion of NMTC. Molecular studies are needed to determine the genetic basis of cancer susceptibility in these families.

Family cancer history and susceptibility to oral carcinoma in Puerto Rico

BACKGROUND

Use of alcohol and tobacco are the major risk factors for cancers of the oral cavity and pharynx in most of the world. A heritable component to oral carcinoma risk also has been suggested, although only limited data are available on familial aggregation of this disease.

METHODS

A population-based case-control study of 342 subjects with carcinomas of the oral cavity and pharynx (oral carcinoma) and 521 controls was conducted in Puerto Rico. The relation between family history of carcinomas of the oral cavity, the upper aerodigestive tract (UADT), and other selected sites with risk of oral carcinoma was explored using logistic regression modeling techniques.

RESULTS

Risk of oral carcinoma was elevated for subjects reporting a first-degree relative with carcinoma of the oral cavity (odds ratio [OR], 2.5; 95% confidence interval [CI], 0.8-8.0) or any UADT carcinoma (OR, 2.6; 95% CI, 1.4-4.8). The increased risk associated with family history of UADT carcinoma tended to be greatest for subjects with known risk factors (i.e., heavy consumption of alcohol and/or tobacco and infrequent intake of raw fruits and vegetables) and with oral carcinoma diagnoses at ages younger than 65 years.

CONCLUSIONS

These findings are consistent with a heritable component to oral carcinoma, although shared lifestyle risk factors may be partially involved.

A systematic review and meta-analysis of familial colorectal cancer risk

OBJECTIVE

The aim of this study was to identify published studies quantifying familial colorectal cancer (CRC) risks in first-degree relatives of CRC and colorectal adenoma (CRA) cases and, through a meta-analysis, obtain more precise estimates of familial risk according to the nature of the family history and type of neoplasm.

METHODS

Twenty-seven case-control and cohort studies were identified, which reported risks of CRC in relatives of CRC cases and nine, which reported the risk of CRC in relatives of CRA cases. Pooled estimates of risk for various categories of family history were obtained by calculating the weighted average of the log relative risk estimates from studies.

RESULTS

The pooled estimates of relative risk were as follows: a first-degree relative with CRC 2.25 (95% CI = 2.00-2.53), colon 2.42 (95% CI = 2.20-2.65), and rectal 1.89 (95% CI = 1.62-2.21) cancer; parent with CRC 2.26 (95% CI = 1.87-2.72); sibling with CRC 2.57 (95% CI = 2.19-3.02); more than one relative with CRC 4.25 (95% CI = 3.01-6.08); relative diagnosed with CRC before age 45, 3.87 (95% CI = 2.40-6.22); and a relative with CRA 1.99 (95% CI = 1.55-2.55).

CONCLUSIONS

Individuals with a family history of CRC and CRA have a significantly elevated risk of developing CRC compared with those without such a history. Risks are greatest for relatives of patients diagnosed young, those with two or more affected relatives, and relatives of patients with colonic cancers.

RET rearrangements in familial papillary thyroid carcinomas

Familial papillary thyroid carcinoma (FPTC) is an inherited tumor characterized by a more aggressive phenotype than that of its sporadic counterpart. Its mode of inheritance as well as its genetic and molecular bases are still poorly understood. On the contrary, genetic alterations in sporadic papillary thyroid carcinoma (PTC) are better characterized, the most common one involving the activation of the proto-oncogene RET through somatic rearrangements. In the present study, we investigated by interphase fluorescence in situ hybridization the presence of RET rearrangements in a series of 20 FPTC. We show that one FPTC and the adenoma from the same patient carry a RET rearrangement (type PTC1) and that this rearrangement is absent in the germline. Furthermore, we excluded a RET haplotype sharing in two brothers of the same family. These results show that RET rearrangements can indeed be found in FPTC and confirm that RET is not involved in the inherited predisposition to FPTC.

Germline mutations in the p73 gene do not predispose to familial prostate-brain cancer

BACKGROUND

Analysis of high-risk prostate cancer (PC) families with at least one confirmed case of primary brain cancer (BC) has identified a region of genetic linkage on chromosome 1p36 termed CAPB. The p36 region of chromosome one has been reported to have frequent loss of heterozygosity (LOH) in brain and central nervous system (CNS) tumors and epidemiological studies have shown an increased relative risk of BC and tumors of the CNS in PC families. In 1997 a reported tumor suppressor with high homology to p53, termed p73, was mapped to the p36 region of chromosome one. Here, we examine the p73 gene as a potential candidate for CAPB.

METHODS

Ninety-four members from the 12 prostate-brain cancer families in which linkage was originally found were examined. The complete coding region and intron-exon boundaries of the p73 gene were analyzed for germline mutations by Single Stranded Conformational Polymorphism analysis (SSCP) and direct DNA sequencing.

RESULTS

Silent nucleotide substitutions only were detected within the coding regions of the gene in affected individuals. Nucleotide changes were detected in introns 1, 6, 8, 9, and 10, but all were located >or=16 base pairs from the splice site, and are thus unlikely to be deleterious mutations.

CONCLUSIONS

Germline mutations in the p73 gene are unlikely to be critical for inherited susceptibility to PC in this specified subset of families.

A case-control study of the androgen receptor gene CAG repeat polymorphism in Australian prostate carcinoma subjects

BACKGROUND

The development of prostate carcinoma is androgen-dependent. The coding sequence of the androgen receptor (AR) gene contains a CAG repeat polymorphism that has been shown to influence AR activity in vitro. Studies of this polymorphism as a prostate carcinoma risk factor have been conflicting.

METHODS

A matched case-control design was used in a clinic-based multicenter study of Australian prostate carcinoma subjects. Cancer subjects were matched by age and locality with controls, all of whom had a serum prostate specific antigen (PSA) level of less than 4 mg/L. Conditional logistic regression was used to determine the relative risk of prostate carcinoma dependent on AR gene CAG number. The association of disease characteristics at diagnosis with the polymorphism also was assessed.

RESULTS

Five hundred forty-five cases of prostate carcinoma and 456 matched case-control pairs were recruited. Association studies of disease characteristics at diagnosis showed age at diagnosis to be associated with AR CAG number by univariate (P = 0.004) and multivariate (adjusting for PSA, stage, and grade) linear regression (P = 0.018). No association was observed between the polymorphism and disease stage (TNM-based categories; P = 0.277), histologic grade (P = 0.41), or PSA level at diagnosis (P = 0.48). In the pairwise case-control analysis, the odds ratio of prostate carcinoma for a change of 5 CAG repeats gave an odds ratio of 0.9821 (95% confidence interval, 0.84-1.15).

CONCLUSIONS

In this Australian study population, the AR CAG repeat polymorphism was not a risk factor for prostate carcinoma, but a shorter repeat sequence was associated with earlier age at diagnosis.

Risk factors for squamous cell carcinoma of the oral cavity in young people--a comprehensive literature review

There have been several reports of a rising incidence of oral cancer from many parts of the world. Although it is well known that oral cancer increases with age, recent trends for a rising incidence particularly relates to cancer of the tongue and mouth in young males. This review critically examines 46 publications devoted to oral cancer in the young adult. Most studies suggest that 4-6% of oral cancers now occur at ages younger than 40 years. Several studies examining risk factors for oral cancer in the young provide evidence that many younger patients have never smoked or consumed alcohol, which are recognised risk factors in older groups, or that duration of exposure may be too short for malignant transformation to occur. Information on many aspects of aetiology for this disease in the young implicating occupational, familial risk, immune deficits and virus infection are meagre. The spectrum of genetic abnormality disclosed is similar to older patients, there is paucity of specific studies involving younger cohorts, but predisposition to genetic instability has been hypothesised as a likely cause. Conflicting evidence is also reported on the sex distribution and outcome compared with older patients. Much work is required to understand the caveats related to global demography, risk factors and their diagnostic and prognostic markers for this disease which might be considered a disease distinct from that occurring in older patients.

Localization of a susceptibility gene for familial nonmedullary thyroid carcinoma to chromosome 2q21

The familial form of nonmedullary thyroid carcinoma (NMTC) is a complex genetic disorder characterized by multifocal neoplasia and a higher degree of aggressiveness than its sporadic counterpart. In a large Tasmanian pedigree (Tas1) with recurrence of papillary thyroid carcinoma (PTC), the most common form of NMTC, an extensive genomewide scan revealed a common haplotype on chromosome 2q21 in seven of the eight patients with PTC. To verify the significance of the 2q21 locus, we performed linkage analysis in an independent sample set of 80 pedigrees, yielding a multipoint heterogeneity LOD score (HLOD) of 3.07 (alpha=0.42), nonparametric linkage (NPL) 3.19, (P=.001) at marker D2S2271. Stratification based on the presence of at least one case of the follicular variant of PTC, the phenotype observed in the Tas1 family, identified 17 such pedigrees, yielding a maximal HLOD score of 4.17 (alpha=0.80) and NPL=4.99 (P=.00002) at markers AFMa272zg9 and D2S2271, respectively. These results indicate the existence of a susceptibility locus for familial NMTC on chromosome 2q21.

A genome screen of families with multiple cases of prostate cancer: evidence of genetic heterogeneity

We conducted a genomewide screen for prostate cancer-susceptibility genes on the basis of data from 98 families from the United States and Canada that had three or more verified diagnoses of prostate cancer among first- and second-degree relatives. We found a statistically significant excess of markers for which affected relatives exhibited modest amounts of excess allele-sharing; however, no single chromosomal region contained markers with excess allele-sharing of sufficient magnitude to indicate unequivocal evidence of linkage. Positive linkage signals of nominal statistical significance were found in two regions (5p-q and 12p) that have been identified as weakly positive in other data sets and in region 19p, which has not been identified previously. All these signals were considerably stronger for analyses restricted to families with mean age at onset below the median than for analyses of families with mean age at onset above the median. The data provided little support for any of the putative prostate cancer-susceptibility genes identified in other linkage studies.

Consanguinity and family history of cancer in children with leukemia and lymphomas

BACKGROUND

In native population of the United Arab Emirates (UAE), the rate of consanguineous marriages is 50.5%. This study was designed to determine whether the rates of consanguinity and family history of cancer among the families of children with lymphoid malignancy are different from those in the general population.

METHODS

The study comprised 117 patients from the whole of the country with acute lymphocytic leukemia (ALL) and Hodgkin lymphoma (HL) and non-Hodgkin lymphoma (NHL), ranging in age from 2 to 14 years. The consanguinity rate in the study group was compared with the rate in the general population. To study family history of cancer, the authors matched patients with 117 controls. In a telephone interview, each mother was asked to provide data regarding the biologic relationship between her and her husband as well as that between both sets of grandparents; each was also asked whether any family relative had a cancer and, if so, of what type.

RESULTS

Among the 69 ALL cases, 80% of families were consanguineous and 20% were nonconsanguineous. Among the 26 NHL and 22 HL cases, each group included 3 consanguineous families, 12% and 14%, respectively. The consanguinity rates for ALL, NHL, and HL were all significantly different from the 50.5% consanguinity rate in the UAE population (all three P values < 0.0001). The family history of cancer was more often positive in ALL patients than in controls (odds ratio, 2.14; confidence interval, 1.01--4.53). Overall and for each lymphoid malignancy, there was no difference in family history of cancer between consanguineous and nonconsanguineous groups of cases.

CONCLUSIONS

The consanguinity rate in the families of patients with ALL is significantly higher and in those with NHL and HL significantly lower than that in the UAE population. The family history of cancer is more often positive among ALL cases than controls--consanguinity having no effect.

Family history of cancer and risk of esophageal and gastric cancers in the United States

The worldwide rates for histology- and subsite-specific types of esophageal and gastric cancer reveal strikingly divergent patterns. The contribution of environmental and genetic factors has been explored in several high-incidence areas, but data on genetic influences are scarce for Western countries. Using data from a multicenter, population-based, case-control study on 1,143 cases and 695 controls in the United States, we evaluated whether a family history of digestive or other cancers was associated with an increased risk of esophageal adenocarcinoma (n = 293), esophageal squamous cell carcinoma (n = 221), gastric cardia adenocarcinoma (n = 261) or non-cardia gastric adenocarcinoma (n = 368). After adjusting for other risk factors, individuals reporting a family history of digestive cancers experienced no increased risk of either type of esophageal cancer but they were prone to adenocarcinomas of the gastric cardia [odds ratio (OR) = 1.34, 95% confidence interval (CI) 0.91-1.97] and non-cardia segments (OR =1.46, 95% CI 1.03-2.08). This familial tendency, particularly for non-cardia gastric tumors, was largely explained by an association with family history of stomach cancer (OR = 2.52, 95% CI 1.50-4.23). In addition, family history of breast cancer was associated with increased risks of esophageal adenocarcinoma (OR = 1.74, 95% CI 1.07-2.83) and non-cardia gastric adenocarcinoma (OR = 1.76, 95% CI 1.09-2.82). Also seen were non-significant familial associations of esophageal squamous-cell cancer with prostate cancer as well as non-cardia gastric cancer with leukemia and brain tumors, though these relationships must be interpreted with caution. Our data point to the role of familial susceptibility to gastric cancer, but not to any form of esophageal cancer, in the United States.

Segregation analyses of 1,476 population-based Australian families affected by prostate cancer

Segregation analyses aim to detect genetic factors that have a major effect on an individual's risk of disease and to describe them in terms of mode of inheritance, age-specific cumulative risk (penetrance), and allele frequency. We conducted single- and two-locus segregation analyses of data from 1,476 men with prostate cancer diagnosed at age <70 years and ascertained through population registries in Melbourne, Sydney, and Perth, Australia, and from their brothers, fathers, and both maternal and paternal lineal uncles. Estimation and model selection were based on asymptotic likelihood theory and were performed through use of the software MENDEL. All two-locus models gave better fits than did single-locus models, even if lineal uncles were excluded or if we censored data (age and disease status) for relatives at 1992, when prostate-specific-antigen testing started to have a major impact on the incidence of prostate cancer in Australia. Among the genetic models that we considered, the best-fitting ones included a dominantly inherited increased risk that was greater, in multiplicative terms, at younger ages, as well as a recessively inherited or X-linked increased risk that was greater, in multiplicative terms, at older ages. The recessive and X-linked effects were strongly confounded, and it was not possible to fit them together. Penetrance to age 80 years was approximately 70% (95% confidence interval [CI] 57%-85%) for the dominant effect and virtually 100% for the recessive and X-linked effects. Approximately 1/30 (95% CI 1/80-1/12) men would carry the dominant risk, and 1/140 (95% CI 1/220-1/90) would carry the recessive risk or 1/200 (95% CI 1/380-1/100) would carry the X-linked risk. Within discussed limitations, these analyses confirm the genetic heterogeneity, of prostate cancer susceptibility, that is becoming evident from linkage analyses, and they may aid future efforts in gene discovery.

Familial/bilateral and sporadic testicular germ cell tumors show frequent genetic changes at loci with suggestive linkage evidence

Testicular germ cell tumor (TGCT) is the most common tumor type among adolescent and young adult males. Familial clustering and bilateral disease are suggestive of a genetic predisposition among a subgroup of these patients, but susceptibility genes for testicular cancer have not yet been identified. However, suggestive linkage between disease and genetic markers has been reported at loci on chromosome arms 3q, 5q, 12q, 18q, and Xq. We have analyzed primary familial/bilateral (n=20) and sporadic (n=27) TGCTs, including 28 seminomas and 19 nonseminomas, for allelic imbalance (AI) within the autosomal regions. DNA from all tumors were analyzed by fluorescent polymerase chain reaction of 22 polymorphic loci at 3q27-ter, 5q13-35.1, 12q21-ter, and 18q12--ter. All tumor genotypes were evaluated against their corresponding constitutional genotypes. The percentages of TGCTs with genetic changes at 3q, 5q, 12q, and 18q, were 79%, 36%, 53% and 43%, respectively. The frequencies at 3q and 12q in nonseminomas were significantly higher than in seminomas (P=.003 and P=.004). In order to evaluate changes at hemizygous Xq loci, five loci were analyzed by co-amplification with an autosomal reference marker known to reveal retained heterozygosity in the tumor DNA. Gain of Xq sequences was seen in more than 50% of the tumors. The degree of amplification varied among the loci in each of five tumors, and based on these breakpoints, a common region of overlapping gains was found at Xq28. No significant differences were found between the frequencies of genetic changes in familial/bilateral versus sporadic tumors, an observation speaking in disfavor of the existence of a single susceptibility gene for TGCT in any of the analyzed regions. Our data suggest that gain of genetic material at distal Xq and losses at 5q and 18q contribute to establishment of seminomas, whereas imbalances at 3q as well as gain at distal part of 12q are associated with further progression into nonseminomas.

The role of genetic factors in the etiology of pancreatic adenocarcinoma: an update

Pancreatic cancer is a disease with a very poor prognosis and its etiology is still largely elusive. The only consistent environmental risk factor is cigarette smoking. A previous history of pancreatitis or diabetes mellitus is also considered to be a risk factor. Epidemiological studies have confirmed that relatives of those with pancreatic cancer have an increased risk of this malignancy, and it has been evaluated that 3-5% of all pancreatic cancer cases are caused by genetic predisposition to the disease. Usually this occurs in the setting of a known inherited cancer syndrome caused by mutations in genes such as BRCA1/2 and CDKN2A. Whether or not a true site-specific pancreatic adenocarcinoma syndrome exists is not known. The real challenge for the management of high risk patients is to develop new screening methods than can identify pre-neoplastic or early neoplastic lesions in a timely manner.

Familial risk of pancreatic cancer

BACKGROUND

Pancreatic cancer is the fifth leading cause of cancer-related mortality in the United STATES: Although smoking and age are known risk factors for pancreatic cancer, several case reports and case-control studies have suggested that there is also a familial risk. We evaluated whether a family history of pancreatic cancer increases the risk of pancreatic cancer in first-degree relatives and whether smoking and younger age at cancer diagnosis further increase this risk.

METHODS

We conducted in-person interviews with 247 patients ("case probands") with pancreatic cancer and 420 population-based control probands to collect risk factor data and pancreatic cancer family history for 1816 first-degree relatives of the case probands and 3157 first-degree relatives of the control probands. We analyzed the data by unconditional logistic regression models, with adjustment for correlated data by use of generalized estimating equations. All statistical tests were two-sided.

RESULTS

A positive family history of pancreatic cancer (i.e., being related to a case proband) or ever-smoking cigarettes approximately doubled the risk of pancreatic cancer (relative risk [RR] = 2.49; 95% confidence interval [CI] = 1.32 to 4.69; RR = 2.04; 95% CI = 1.09 to 3.83, respectively). The RR increased to 8.23 (95% CI = 2.18 to 31.07) for relatives who ever smoked and were related to a case proband who was diagnosed before age 60 years.

CONCLUSION

Routine questioning of patients about a family history of pancreatic cancer, the age of onset of this cancer in their relatives, and the patient's smoking status may identify individuals at high risk of pancreatic cancer. Future research exploring the genetic and environmental interactions associated with the risk of pancreatic cancer is critically important.

A population-based study of familial cutaneous melanoma

We studied familial risks in cutaneous melanoma by comparing the occurrence of melanoma, or discordant cancer, in two generations, based on the Swedish Family-Cancer Database of 9.6 million individuals. Offspring were from 0 to 61 years of age. Cancers were obtained from the Swedish Cancer Registry for the years 1958 to 1996. The study was based on 30,170 cases of melanoma. Among these, 196 offspring came from families where a parent also presented with melanoma. The overall familial hazard ratio (FHR) was 2.47 when a parent had melanoma; an early age of onset increased the risk. Multiple primary melanomas in parents increased the FHR in offspring, being 2.23 for one, 9.10 for two and up to 83 for more than two melanomas in the parent. The number of affected offspring increased the risk of melanoma in the parents, from 3.05 when one was affected to 5.12 and 151 when two or three offspring were affected, respectively. Melanoma risk to a sibling with an affected proband was 3.56. Melanoma in one generation was associated with an increased occurrence of squamous cell carcinoma of the skin in the other generation. Other weaker associations were found to pancreatic, breast, testicular and nervous system cancers and non-Hodgkin lymphomas.

Sibling risks in cancer: clues to recessive or X-linked genes?

A systematic analysis of cancer risks to offspring and to siblings of cancer cases was carried out based on the nation-wide Swedish Family-Cancer Database. For all 13 cancer sites examined, risks to both offspring and siblings of cases of cancer at the same site were significantly elevated. The relative risk to siblings was approximately 2 fold more than the offspring risk for cancers of the prostate, testis, kidney and bladder, suggesting that recessive or X-linked susceptibility genes may be important for these cancers. Risks to siblings of cases where a parent was also affected were increased >20 fold over population rates for colorectal, ovarian, prostate and renal cancer, and for leukaemia, consistent with the effects of rare high-risk susceptibility alleles.

Prostate cancer genomics

The molecular processes contributing to cancer of the human prostate gland are under intensive investigation. Methods used for discovering genetic alterations involved in prostate neoplasia include family studies designed to map hereditary disease loci, chromosomal studies to identify aberrations that may locate oncogenes or tumor suppressor genes, and comprehensive gene expression studies. These studies determine how various molecular signaling pathways influence or reflect the process of carcinogenesis. However, a comprehensive overview of the cell is necessary to understand all of the dynamic interactions between genes, their protein products, and the network of cellular processes resulting in tumorigenesis. Unraveling the complexity of these systems in a timely manner involves the integration of computers, miniaturization, and automation into molecular biology. New biotechnologies such as the development of automated DNA sequencing and complementary DNA microarrays allow for a systematic, "discovery-driven" approach. These and other technologies afford a comprehensive view of biology and pathology that have the potential to fully characterize the processes involved in neoplasia and therefore provide potential targets for the therapy of prostate and other cancers.

Cancer risks to spouses and offspring in the Family-Cancer Database

It is generally accepted that cancer is caused by environmental and inherited factors but these are only partially identified. Family studies can be informative but they do not separate shared lifestyles and genes. We estimate familial risks for concordant cancers between spouses in common cancers of both sexes in order to quantify cancer risks from the shared environment. The risks are compared to those seen between parents and offspring in order to estimate the inherited component. The nation-wide Family-Cancer Database was used as the source of family and cancer data. Standardized incidence ratios (SIRs) were calculated for concordant cancer in offspring by parental cancer and in spouses. Among the 23 cancer sites considered, all but two showed an increased SIR for offspring by father or mother. Only two sites, stomach and lung, showed an increase in SIR of concordant cancer among spouses. Additionally, pancreatic cancer and melanoma were increased in couples where at least one spouse was diagnosed before age 50. If both spouses presented melanoma before age 40, SIR was 3.82 for husbands. SIRs of colon, renal, and skin (squamous cell) cancers were unchanged by spouses' concordant cancer. Shared lifestyle among spouses seems to explain only a small proportion of cancer susceptibility. Because lifestyles are likely to differ more between parents and offspring than between spouses, familial cancer risks between parents and offspring are likely to be more due to heritable rather than environmental effects.

Genetic epidemiology of multistage carcinogenesis

It is commonly believed that cancer is a multistage, polygenic disease. Even though conceptually appealing, the evidence supporting the multistage theory remains limited. Most known tumor suppresser genes are associated with monogenic dominant cancers following a two-hit pathway. We review results from a recent twin study on 90000 individuals that give support to the multistage theory. Statistically significant heritability estimates were shown for cancers of the colorectum (35%), breast (27%), and prostate (42%). These estimates are much higher than those obtained from family studies in which parents and offspring, or sibs are compared. The difference can be accounted for by the involvement of many genes. A polygenic cancer would show small effects in family studies but large effects in twin studies. We present calculations on the decrease in familial risks when the number of genes involved increases or when the penetrance decreases. We test the apparent number of stages involved in the main cancers from the Swedish Family-Cancer Database. The logarithms of the slopes suggest large differences in the apparent numbers of mutations involved in different cancers. The number of mutations required appears to be less in familial breast cancer compared to sporadic breast cancer. Study designs for gene identification should be revised to accommodate polygenic cancers.