Genetic epidemiology of multistage carcinogenesis

Isolation of cytotoxic monomeric protein and morin derivatives from Solena amplexicaulis (Lam.) Gandhi

Solena amplexicaulis (Lam.) Gandhi (family- Cucurbitaceae), is used both in the Indian traditional system and folk medicine to treat several pathophysiological conditions and complex diseases including cancer. The screening of the phytochemicals of this plant (aerial parts) was performed to evaluate their cytotoxic effect against an in vitro cancer model utilising acute promyelocytic leukaemia HL60 cell line. Phytoconstituents were isolated by column chromatography and characterised. The purified protein was extracted, isolated and purified by using standard techniques. The cytotoxicity was evaluated by MTT assay. Spectral analysis revealed the isolated phytochemicals to be Morin-3-O-xyloside (1) and Morin 3-O-glucoside (2). The purified protein (P1) was found to be monomeric having a molecular weight of 30.2 kDa. Watching over 24 h exposure, compound 1 (IC₅₀ 1.5 µmol/L), compound 2 (IC₅₀ 3.5 µmol/L), and P1 (2.67 µmol/L) exhibited significant cytotoxic activity.

Crocus sativus a natural food coloring and flavoring has potent anti-tumor properties

BACKGROUND

Saffron, the dried stigmas of Crocus sativus L., is a highly valued agricultural product that is used mainly as a food coloring and flavoring agent. Three main secondary metabolites of Crocus sativus including crocin, picrocrocin, and safranal are responsible for the color, the bitter taste and for the odor and aroma, respectively. As a component of traditional medicine, saffron has been utilized as a medicinal herb for treating various ailments including cramps, asthma, liver disease, menstruation disorders, pain, and in the pathogenesis of cancer.

HYPOTHESIS/PURPOSE

To summarize the recent published data on the chemo-preventive properties of Crocus sativus in cancer treatment.

STUDY DESIGN

We conducted a non-systematic review of the literature.

METHODS

A search of English-language literature was performed using Scopus, EMBASE and PubMed. We applied no restriction in time. Articles were searched using the keywords "Lung", "breast", "skin", "prostate", "leukemia", "cancer", "neoplasm", "tumor", "malignancy", "saffron", "crocus sativus", "crocin", "crocetin", "picrocrocin", and "safranal".

RESULTS

Saffron has been reported to exert anti-tumor and anti-cancer effects in various types of cancer including lung cancer, breast cancer, leukemia, skin cancer and prostate cancer. This appears to be via various mechanisms including: the induction of apoptosis, arresting cell cycle progression, suppressing expression of matrix metalloproteinase, modulatory effects on some phase II detoxifying enzymes and decreasing expression of inflammatory molecules are potential mechanisms of saffron-induced anticancer effects.

CONCLUSION

Saffron possesses potent anti-tumor properties and represents an efficacious and safe treatment.

Use of census data for construction of fertility history for Danish women

Background: Modern epidemiology increasingly uses data on families. The authors constructed an extended fertility database for women born in Denmark from 1930 onwards by supplementing the existing Fertility Database with household data from the 1970 census. Methods: A fertility history was constructed for all women participating in the 1970 census, but aiming for complete data only for women aged 20 - 39. The fertility history of these women prior to the 1970 census was constructed from the census data including 1,648,813 persons coded as children. An algorithm was used transforming household information into fertility history data by matching women and children according to family position. Children for whom the algorithm gave no match were searched for in the Fertility Database; children not found in the Fertility Database either were searched for manually. The fertility history after the 1970 census was retrieved from the Fertility Database. Results: Using data from the census 1970, 98.5% of the children were linked to a mother, and 99.6% of these links were estimated to be correct, corresponding to 98.1% of the children being linked correctly. In total, 964,720 children of women aged 20 - 39 in 1970 were identified, which was equivalent to 96.6% of the expected live-born children, and to 99.1% of the expected surviving children. Conclusion: Census household data proved to be an excellent data source for construction of fertility histories.

Transformation assay in Bhas 42 cells: a model using initiated cells to study mechanisms of carcinogenesis and predict carcinogenic potential of chemicals

Transformation assays using cultured cells have been applied to the study of carcinogenesis. Although various cell systems exist, few cell types such as BALB/c 3T3 subclones and Syrian hamster embryo cells have been used to study chemically induced two-stage carcinogenesis. Bhas 42 cells were established as a clone by the transfection with the v-Ha-ras gene into mouse BALB/c 3T3 A31-1-1 cells and their subsequent selection based on their sensitivity to 12-O-tetradecanoylphorbol-13-acetate. Using Bhas 42 cells, transformed foci were induced by the treatment with nongenotoxic carcinogens, most of which act as tumor promoters. Therefore, Bhas 42 cells were considered to be a model of initiated cells. Subsequently, not only nongenotoxic carcinogens but also genotoxic carcinogens, most of which act as tumor initiators, were found to induce transformed foci by the modification of the protocol. Furthermore, transformation of Bhas 42 cells was induced by the transfection with genes of oncogenic potential. We interpret this high sensitivity of Bhas 42 cells to various types of carcinogenic stimuli to be related to the multistage model of carcinogenesis, as the transfection of v-Ha-ras gene further advances the parental BALB/c 3T3 A31-1-1 cells toward higher transforming potential. Thus, we propose that Bhas 42 cells are a novel and sensitive cell line for the analysis of carcinogenesis and can be used for the detection of not only carcinogenic substances but also gene alterations related to oncogenesis. This review will address characteristics of Bhas 42 cells, the transformation assay protocol, validation studies, and the various chemicals tested in this assay.

A Rb1 promoter variant with reduced activity contributes to osteosarcoma susceptibility in irradiated mice

BACKGROUND

Syndromic forms of osteosarcoma (OS) account for less than 10% of all recorded cases of this malignancy. An individual OS predisposition is also possible by the inheritance of low penetrance alleles of tumor susceptibility genes, usually without evidence of a syndromic condition. Genetic variants involved in such a non-syndromic form of tumor predisposition are difficult to identify, given the low incidence of osteosarcoma cases and the genetic heterogeneity of patients. We recently mapped a major OS susceptibility QTL to mouse chromosome 14 by comparing alpha-radiation induced osteosarcoma in mouse strains which differ in their tumor susceptibility.

METHODS

Tumor-specific allelic losses in murine osteosacoma were mapped along chromosome 14 using microsatellite markers and SNP allelotyping. Candidate gene search in the mapped interval was refined using PosMed data mining and mRNA expression analysis in normal osteoblasts. A strain-specific promoter variant in Rb1 was tested for its influence on mRNA expression using reporter assay.

RESULTS

A common Rb1 allele derived from the BALB/cHeNhg strain was identified as the major determinant of radiation-induced OS risk at this locus. Increased OS-risk is linked with a hexanucleotide deletion in the promoter region which is predicted to change WT1 and SP1 transcription factor-binding sites. Both in-vitro reporter and in-vivo expression assays confirmed an approx. 1.5 fold reduced gene expression by this promoter variant. Concordantly, the 50% reduction in Rb1 expression in mice bearing a conditional hemizygous Rb1 deletion causes a significant rise of OS incidence following alpha-irradiation.

CONCLUSION

This is the first experimental demonstration of a functional and genetic link between reduced Rb1 expression from a common promoter variant and increased tumor risk after radiation exposure. We propose that a reduced Rb1 expression by common variants in regulatory regions can modify the risk for a malignant transformation of bone cells after radiation exposure.

Cytochrome P450-isoenzyme 1A1 in susceptibility to tobacco-related lung cancer

BACKGROUND

Tobacco smoke contains many carcinogens that may mediate susceptibility to lung cancer. Cytochrome P450 isoenzyme 1A1 activity and expression increases several fold in lung cancer due to smoking. Finding the role of cytochrome P450 1A1 in susceptibility to tobacco-related lung cancer may be important to predict the outcome in early stage cancer, and may result in an improved survival rate.

PATIENTS AND METHODS

This study was carried on 2 groups of patients: group A was 20 patients with operable smoking-related lung cancer, who underwent surgery at the time of diagnosis; group B was 20 nonsmokers without lung cancer who underwent chest exploration following road traffic accidents. Specimens were obtained from tumor tissue and surrounding healthy tissue in group A patients, and from healthy lung tissue in group B patients. These specimens were sent for measurement of protein content and cytochrome P450 1A1 activity.

RESULTS

There was significantly greater tissue cytochrome P450 1A1 activity in group A compared to group B. Patients with stage II cancer showed significantly higher levels of tissue cytochrome P450 1A1 activity than those with stage I. There was also a significant difference in tissue cytochrome P450 1A1 activity between the tumor tissue and the tissue surrounding the tumor.

CONCLUSION

Carcinogens in smoke increase cytochrome P450 1A1 activity, which might be considered to play a role in cigarette smoking-induced lung cancer.

A mathematical model for predicting malignancy of solitary pulmonary nodules

BACKGROUND

The goal of the present study was to differentiate between benign and malignant solitary pulmonary nodules (SPN) by developing a mathematical prediction model.

METHODS

Records from 371 patients (197 male, 174 female) with SPN between January 2000 and September 2009 were reviewed (group A). Clinical data were collected to estimate the independent predictors of malignancy of SPN with multivariate logistic regression analysis. A clinical prediction model was subsequently developed. Between October 2009 and May 2011, data from an additional 145 patients with SPN were used to validate this new clinical prediction model (group B). The same data were also estimated with two previously published models for comparison with our new model.

RESULTS

The median patient age was 57.1 years in group A; 54% of the nodules were malignant and 46% were benign. Logistic regression analysis identified six clinical characteristics (age, diameter, border, calcification, spiculation, and family history of tumor) as independent predictors of malignancy in patients with SPN. The area under the receiver operator characteristic (ROC) curve for our model (0.874 ± 0.028) was higher than those generated using the other two reported models. In our model, sensitivity = 94.5%, specificity = 70.0%, positive predictive value = 87.8%, and negative predictive value = 84.8%).

CONCLUSIONS

Age, diameter, border, calcification, spiculation, and family history of tumor were independent predictors of malignancy in patients with SPN. Our prediction model was sufficient to estimate malignancy in patients with SPN and proved to be more accurate than the two existing models.

Genetic architecture of cancer and other complex diseases: lessons learned and future directions

Genome-wide association studies have broadened our understanding of the genetic architecture of cancer to include common variants, in addition to the rare variants previously identified by linkage analysis. We review current knowledge on the genetic architecture of four cancers--breast, lung, prostate and colorectal--for which the balance of common and rare alleles identified ranges from fewer common alleles (lung cancer) to more common alleles (prostate cancer). Although most variants are cancer specific, pleiotropy has been observed for several variants, for example, variants at the 8q24 locus and breast, ovarian and prostate cancers or variants in KITLG in relation to hair color and testicular cancer. Although few studies have been adequately powered to investigate heterogeneity among ancestry groups, effect sizes associated with common variants have been reported to be fairly homogenous among ethnic groups. Some associations appear to be ancestry specific, such as HNF1B, which is associated with prostate cancer in European Americans and Latinos but not in African-Americans. Studies of cancer and other complex diseases suggest that a simple dichotomy between rare and common allelic architectures may be too simplistic and that future research is needed to characterize a fuller spectrum of allele frequency (common (>5%), uncommon (1-5%) and rare (<<1%) alleles) and effect size. In addition, a broadening of the concept of genetic architecture to encompass both population architecture, which reflects differences in exposures, genetic factors and population level risk among diverse groups of people, and genomic architecture, which includes structural, epigenomic and somatic variation, is envisioned.

Risks for Familial and Contralateral Breast Cancer Interact Multiplicatively and Cause a High Risk

The reasons for the high risk of contralateral breast cancer are not understood, although polygenic mechanisms have been suggested to be involved. The nationwide Swedish Family-Cancer Database was used to examine the interaction of the risks for contralateral and familial cancer. Relative risks were separately determined for contralateral and familial breast cancers, and these were tested for additive and multiplicative interactions. The Database contained information on 102,176 first breast cancers. Familial risk for breast cancer was 1.76 and the risk for contralateral breast cancer was 3.40, or 5.80 when extrapolated to two breasts. When women had a family history, the risk for contralateral breast cancer was remarkably high, 5.48, or 9.96 when the risk was extrapolated to two breasts, almost identical with 10.21, which was predicted by the multiplicative model. Although the data do not rule out polygenic mechanisms, they suggest that epigenetic imprinting events may be involved for the contralateral breast cancer.

Genetic Programming Neural Networks: A Powerful Bioinformatics Tool for Human Genetics

The identification of genes that influence the risk of common, complex disease primarily through interactions with other genes and environmental factors remains a statistical and computational challenge in genetic epidemiology. This challenge is partly due to the limitations of parametric statistical methods for detecting genetic effects that are dependent solely or partially on interactions. We have previously introduced a genetic programming neural network (GPNN) as a method for optimizing the architecture of a neural network to improve the identification of genetic and gene-environment combinations associated with disease risk. Previous empirical studies suggest GPNN has excellent power for identifying gene-gene and gene-environment interactions. The goal of this study was to compare the power of GPNN to stepwise logistic regression (SLR) and classification and regression trees (CART) for identifying gene-gene and gene-environment interactions. SLR and CART are standard methods of analysis for genetic association studies. Using simulated data, we show that GPNN has higher power to identify gene-gene and gene-environment interactions than SLR and CART. These results indicate that GPNN may be a useful pattern recognition approach for detecting gene-gene and gene-environment interactions in studies of human disease.

The effect of reduction in cross-validation intervals on the performance of multifactor dimensionality reduction

Multifactor Dimensionality Reduction (MDR) was developed to detect genetic polymorphisms that present an increased risk of disease. Cross-validation (CV) is an important part of the MDR algorithm, as it prevents over-fitting and allows the predictive ability of a model to be evaluated. CV is a computationally intensive step in the MDR algorithm. Traditionally, MDR has been implemented using 10-fold CV. In order to reduce computation time and therefore allow MDR analysis to be applied to larger datasets, we evaluated the possibility of eliminating or reducing the number of CV intervals used for analysis. We found that eliminating CV made final model selection impossible, but that reducing the number of CV intervals from ten to five caused no loss of power, thereby reducing the computation time of the algorithm by half. The validity of this reduction was confirmed with data from an Alzheimer's disease (AD) study.

Multilocus inheritance determines predisposition to α-radiation induced bone tumourigenesis in mice

In a recent study, we presented evidence for genetic predisposition governing radiation osteosarcomagenesis in mice. Following the incorporation of the bone-seeking alpha emitter 227Th, approximately 25% of the variance in osteosarcoma incidence was determined by inherited genetic factors. We have now mapped 5 susceptibility loci in crosses between the more susceptible BALB/c and the more resistant CBA/Ca strains. The major QTL on chromosome 14 overlaps with a locus that was already found in our previous study, using different strains of mice. Here, we investigate the effect by which the major susceptibility locus and 4 minor modifier loci interact to influence osteosarcoma predisposition. Following incorporation of the bone-seeking isotope, 100% of mice that harbour high-risk genotypes at all 5 susceptibility loci develop osteosarcoma with an average of 472 days latency times. In 10 mice inheriting exclusively low-risk genotypes only 1 osteosarcoma was found, arising after 733 days latency time. Inheritance of distinct combinations of BALB/c and CBA/Ca alleles at the susceptibility loci confer more extreme phenotypes in terms of susceptibility or resistance than observed in either of the two parental inbred strains. From the present study, we demonstrate that additive effects of multiple alleles, each making only a minor phenotypic contribution, can combine and significantly alter tumour risk. This mechanism can be of particular importance in genetically heterogeneous populations such as man.

GPNN: power studies and applications of a neural network method for detecting gene-gene interactions in studies of human disease

Background

The identification and characterization of genes that influence the risk of common, complex multifactorial disease primarily through interactions with other genes and environmental factors remains a statistical and computational challenge in genetic epidemiology. We have previously introduced a genetic programming optimized neural network (GPNN) as a method for optimizing the architecture of a neural network to improve the identification of gene combinations associated with disease risk. The goal of this study was to evaluate the power of GPNN for identifying high-order gene-gene interactions. We were also interested in applying GPNN to a real data analysis in Parkinson's disease.

Results

We show that GPNN has high power to detect even relatively small genetic effects (2–3% heritability) in simulated data models involving two and three locus interactions. The limits of detection were reached under conditions with very small heritability (<1%) or when interactions involved more than three loci. We tested GPNN on a real dataset comprised of Parkinson's disease cases and controls and found a two locus interaction between the DLST gene and sex.

Conclusion

These results indicate that GPNN may be a useful pattern recognition approach for detecting gene-gene and gene-environment interactions.

Genome wide in silico SNP-tumor association analysis

Background

Carcinogenesis occurs, at least in part, due to the accumulation of mutations in critical genes that control the mechanisms of cell proliferation, differentiation and death. Publicly accessible databases contain millions of expressed sequence tag (EST) and single nucleotide polymorphism (SNP) records, which have the potential to assist in the identification of SNPs overrepresented in tumor tissue.

Methods

An in silico SNP-tumor association study was performed utilizing tissue library and SNP information available in NCBI's dbEST (release 092002) and dbSNP (build 106).

Results

A total of 4865 SNPs were identified which were present at higher allele frequencies in tumor compared to normal tissues. A subset of 327 (6.7%) SNPs induce amino acid changes to the protein coding sequences. This approach identified several SNPs which have been previously associated with carcinogenesis, as well as a number of SNPs that now warrant further investigation

Conclusions

This novel in silico approach can assist in prioritization of genes and SNPs in the effort to elucidate the genetic mechanisms underlying the development of cancer.

Genetic epidemiology of cancer: From families to heritable genes

A reliable determination of familial risks for cancer is important for clinical counseling, prevention and understanding cancer etiology. Family-based gene identification efforts may be targeted if the risks are well characterized and the mode of inheritance is identified. Medically verified data on familial risks have not been available for all types of cancer but they have become available through the use of the nationwide Swedish Family-Cancer Database, which includes all Swedes born in 1932 and later with their parents, totaling over 10 million individuals. Over 150 publications have emanated from this source. The familial risks of cancer have been characterized for all main cancers and the contribution of environmental and heritable effects to the familial aggregation has been assessed. Furthermore, the mode of inheritance has been deduced by comparing risks from parental and sibling probands. Examples are shown on familial clustering of cancers, for which heritable susceptibility genes are yet unknown, such as squamous cell carcinoma of the skin, intestinal carcinoids, thyroid papillary tumors, brain astrocytomas and pituitary adenomas. Some common cancers, such as lung and kidney cancers, appear to show an early-onset recessive component because familial risks among siblings are much higher than those in families where parents are probands. Many of the cancer sites showing high familial risks lack guidelines for clinical counseling or action level. In conclusion, we recommend that any future gene identification efforts, either using linkage or association designs, devise their strategies based on data from family studies. Clinical genetic counseling would benefit from reviewing established familial risks on all main types of cancer.

A subset of familial colorectal neoplasia kindreds linked to chromosome 9q22.2-31.2

Colorectal cancer is the second most leading cause of cancer death among adult Americans. Two autosomal dominant hereditary forms of the disease, familial adenomatous polyposis and hereditary nonpolyposis colorectal cancer, together account for perhaps 5% of all cases. However, in approximately 20% of additional colon cancer cases, the affected individuals report a family history of colon cancer in a first-degree relative. Similar familial clusters of colon cancer and early-onset colon adenomas have also been reported. To determine whether such familial aggregations arise by chance or reflect a hereditary colon cancer susceptibility, we conducted a whole genome scan to test for genetic linkage in 53 kindreds in which two or more siblings were affected by age 65 or younger with colon cancer or with advanced colon adenomas that were >1 cm in size or that showed high-grade dysplasia. In this cohort we found genetic linkage of disease (P = 0.00045) to chromosomal region 9q22.2-31.2 in a pattern consistent with autosomal dominant disease alleles. These data suggest that a single locus can contribute to disease susceptibility in a subset of patients with nonsyndromic forms of familial colorectal neoplasia.

Evidence of a preferred molecular pathway in patients with synchronous colorectal cancer

BACKGROUND

A small proportion of patients with colorectal carcinoma (CRC) have synchronous tumors at the time of diagnosis. A subset of sporadic CRCs display microsatellite instability (MSI) that is associated with MLH1 silencing due to promoter methylation. In the current study, the authors investigated the proportion of tumors with MSI in patients with synchronous colorectal carcinoma (SCRC) and the concordance in MSI status among tumors in a given individual. In addition, the authors examined MLH1 and MSH2 expression and MLH1 promoter methylation in SCRCs.

METHODS

The current study included 77 patients, with a combined total of 170 invasive SCRCs, who were identified from a database of 2884 patients with CRC. Instability was determined by polymerase chain reaction (PCR) amplification using a set of five markers. Tumors that were unstable at two or more markers were considered unstable (MSI); otherwise, they were considered microsatellite stable (MSS). Expression of MLH1 and MSH2 was determined by immunohistochemistry. Methylation of the MLH1 gene promoter was determined by a methylation-specific PCR assay. Statistical comparisons were made using the chi-square test or the Student t test.

RESULTS

Of the 77 patients in the study, 21 (27%) had a family history of hereditary nonpolyposis colon carcinoma-related malignancy, but none fulfilled the Amsterdam II criteria. Fifty-four of 170 tumors (32%) were found to be MSI. Patients with MSI tumors were older and more frequently female. All but 1 MSI tumor lacked expression of MLH1 (n = 44) or MSH2 (n = 8), or both (n = 1). All MLH1-negative tumors, compared with only 3 MLH1-positive tumors, were methylated at the MLH1 promoter. Most patients (n = 67; 87%) had either all MSS tumors (n = 48; 62%) or all MSI tumors (n = 19; 25%); 10 patients (13%) had both MSS and MSI tumors. The observed MSI/MSS distribution was significantly different from the distribution expected based on an assumption of independence (P < 0.0001).

CONCLUSIONS

There is a strong concordance in MSI/MSS status among tumors in the same individual. This finding suggests that the tumors in patients with SCRC develop along a preferred molecular pathway.

Familial risk of cancer: Data for clinical counseling and cancer genetics

Familial risks for cancer are important for clinical counseling and understanding cancer etiology. Medically verified data on familial risks have not been available for all types of cancer. The nationwide Swedish Family-Cancer Database includes all Swedes born in 1932 and later (0-to 68-year-old offspring) with their parents, totaling over 10.2 million individuals. Cancer cases were retrieved from the Swedish Cancer Registry up to year 2000. Standardized incidence ratios (SIR) and 95% confidence limits (CI) were calculated for age-specific familial risk in offspring by an exact proband status. The familial risks for offspring cancer were increased at 24/25 sites from concordant cancer in only the parent, at 20/21 sites from a sibling proband and at 12/12 sites from a parent and sibling proband. The highest SIRs by parent were for Hodgkin's disease (4.88) and testicular (4.26), non-medullary thyroid (3.26), ovarian (3.15) and esophageal (3.14) cancer and for multiple myeloma (3.33). When a sibling was affected, even prostate, renal, squamous cell skin, endocrine, gastric and lung cancer and leukemia showed SIRs in excess of 3.00. The highest cumulative risks were found for familial breast (5.5%) and prostate (4.2%) cancers. We identified reliable familial risks for 24 common neoplasms, most of which lack guidelines for clinical counseling or action level. If, for example, a familial SIR of 2.2 would be use as an action level, counseling would be needed for most cancers at some diagnostic age groups. The present data provide the basis for clinical counseling.

Environmental risk factors for breast cancer among African-American women

There are few unequivocably established environmental carcinogens for breast cancer in women. Nevertheless, environmental factors are believed to explain much of the international variation in breast cancer risk and possibly differences among racial/ethnic groups. Along with lifestyle, some adverse exposures may be higher in minority racial/ethnic groups and in underserved populations that experience higher ambient contamination. Associations have been found between environmental agents and breast cancer in subgroups of women who can be identified by common susceptibility traits as well as by timing of exposures at certain milestones of reproductive life. Susceptibility can be defined by social, environmental, and genetic modalities-factors that may predominate in certain racial/ethnic groups but that also transcend racial/ethnic boundaries. For example, genes involved in transcription and estrogen metabolism have rapid variants that are more prevalent among African-Americans, yet risk accompanying metabolic changes from these genes will prevail in all racial/ethnic groups. Lack of reliable exposure assessment remains a principal obstacle to elucidating the role of environmental exposures in breast cancer. Resources must be identified and consolidated that will enable scientists to improve exposure assessment and to assemble studies of sufficient size to address questions regarding exposure, susceptibility, and vulnerability factors in breast cancer. Breast cancer studies should be expanded to examine combinations of chemicals as well as competing or complementary exposures such as endogenous hormones, dietary intake, and behavioral factors.

High throughput genotyping technologies for pharmacogenomics

Genetic differences between individuals play a role in determining susceptibility to diseases as well as in drug response. The challenge today is first to discover the range of genetic variability in the human population and then to define the particular gene variants, or alleles, that contribute to clinically important outcomes. Consequently, high throughput, automated methods are being developed that allow rapid scoring of microsatellite alleles and single nucleotide polymorphisms (SNPs). Many detection technologies are being used to accomplish this goal, including electrophoresis, standard fluorescence, fluorescence polarization, fluorescence resonance energy transfer, and mass spectrometry. SNP alleles may be distinguished by any one of several methods, including single nucleotide primer extension, allele-specific hybridization, allele-specific primer extension, oligonucleotide ligation assay, and invasive signal amplification. Newer methods require less sample manipulation, increase sensitivity, allow more flexibility, and decrease reagent costs. Recent developments show promise for continuing these trends by combining amplification and detection steps and providing flexible, miniaturized platforms for genotyping.

Skilled use of DNA polymorphisms as a tool for polygenic cancers

Association studies are assumed to be an efficient method of deciding whether a gene or its variant is important for cancer. Sequencing data on 30 000 human genes suggest that an average gene contains one to two single nucleotide polymorphisms (SNP), and high through-put technologies have become available for fast genotyping. Because no functional data are available for most SNPs, the result of the large-scale genotyping effort will be a huge amount of data of unknown biological significance. We discuss here the approaches in study design and reporting that will reduce the spread of false positive data and optimize scientific progress in the genotyping field.

Genetic Epidemiology--science and ethics on familial cancers

Genetic epidemiology provides data on cancer etiology, familial risks and genotype-specific risks. These data are useful for clinical counselling and gene identification. The studies require large, unbiased sample sizes and collaboration between research teams, nationally and internationally. A recent study on Nordic twins suggests that in colorectal, breast and prostate cancer, the inherited component ranges between 27 and 42%, far in excess of the known susceptibility genes. The data from the Swedish Family-Cancer Database, particularly on second cancers, also suggest that a main genetic component in cancer is polygenic. The results have implications for design of genetic studies and for clinical counselling.