Predicting the performance of a genetic testing service for cancer susceptibility

A genetic testing service can determine which members of a population might benefit most from cancer prevention. The eligibility criteria will affect the number of people who use a service and the proportion who test positive. This affects both the service's costs and benefits. The goal of this study was to create computer software that predicts the effect of eligibility restrictions on the performance of a genetic testing service. The software allows eligibility restrictions based on age, gender, and family history of disease. As performance measures, we considered the sensitivity and specificity of eligibility criteria to identify people with genetic cancer susceptibility, the likelihood of genetic susceptibility among people who are eligible for the service, and the likelihood of genetic susceptibility among people who are ineligible. We compared the performance predicted by our model with the observed performance of the Hereditary Cancer Program at the BC Cancer Agency, and studied the effects of changes to model parameters. There was good agreement between model predictions and observed outcomes, however, performance measures were affected by changes to the underlying model parameters. Computer software to predict the performance of a genetic testing service for cancer susceptibility is implemented on the website http://142.103.207.51:8080/gtsim.     

A breast-ovarian cancer susceptibility gene maps to chromosome 17q21.

Nineteen North American Caucasian families that contain a minimum of four confirmed cases of breast or ovarian cancer have been studied. Four polymorphisms (cLB17.1, D17S579, D17S588, and D17S74), which span a region of approximately 15 cM on chromosome 17q12, were typed. Our data confirm the location of a dominant gene conferring susceptibility to breast and ovarian cancer (maximum lod = 9.78) and suggest that the breast-ovarian cancer syndrome is genetically heterogeneous. Two recombinants in one large family suggest that the breast-ovarian cancer locus lies between D17S588 and D17S579.     

Impact of genetic counseling and testing on colorectal cancer screening behavior

One goal of cancer genetic counseling is to improve early detection and prevention of cancers by identifying individuals at risk and providing screening recommendations. This study determined the impact of genetic counseling and testing on patient's post-genetic risk assessment colorectal cancer screening behaviors. Follow-up data from patients seen August, 1996, through May, 1998, at the Johns Hopkins Cancer Risk Assessment Clinic were analyzed. Eligible patients included those without cancer who were due for a colon examination by the time of follow-up, based on recommendations given during genetic risk assessment (GRA). We analyzed the role of gender, age, time since GRA, prior screening, genetic testing decision, mutation status, and post-GRA screening. Of 65 patients evaluated, 50 (76.9%) had undergone at least one endoscopic colon exam prior to visiting the Cancer Risk Assessment Clinic. At the time of GRA, 37 of 65 (56.9%) were overdue for a colon exam and at the time of follow-up, 15/65 (23.1%) were past due (p < 0.001). Patients with mutation-positive genetic tests were more likely to adhere to screening guidelines than those with negative gene tests (100% vs. 40.5%, p = 0.05). Genetic counseling and testing increases overall patient adherence with recommended colon screening, especially for those with positive genetic test results. However, patients with negative results may receive false reassurance about cancer risks and fail to follow recommended screening. Emphasis should be placed on the importance of screening even when genetic test results are negative.     

Psychological impact of genetic testing for breast cancer susceptibility in women of Ashkenazi Jewish background: a prospective study

The recognition that the prevalence of three founder mutations in the BRCA1 and BRCA2 genes is over 2% in Ashkenazi Jews has resulted in numerous epidemiological research studies of this ethno-religious group. To determine the effects of incorporating research into clinical practice, a psychological impact study of women participating in an epidemiological study was conducted. Sixty women of Ashkenazi Jewish background who underwent genetic testing for founder mutations were assessed using mailed, self-administered questionnaires with validated measures of psychological outcome. Forty-three women elected to learn their results and 17 women declined to do so. Women who elected to learn their results were also assessed 7-10 days, 4 months, and 12 months after results disclosure. Women who chose to learn their results had significantly higher baseline breast cancer anxiety, compared to those who elected not to learn their results (z = -2.27; p = 0.023). Unaffected women who elected to learn their results showed a significant decrease in breast cancer anxiety 4 months (z = -2.37, p = 0.018) and 12 months (z = -3.06, p = 0.002) post-notification compared to baseline. Genetic testing for mutations common in Ashkenazi Jewish women with result disclosure does not lead to adverse psychological outcomes.     

Attitude toward genetic testing for cancer risk in Istanbul

To identify attitudes toward genetic testing, and the effects of this information on decisions regarding issues such as pregnancy, abortion, and prophylactic surgery, several subsets of the Turkish population were surveyed in hospital settings. Individuals (n = 179) chosen arbitrarily from four different subsets of a Turkish population were asked to participate in a confidential 23-question survey. Survey participants were familiar with the concept of cancer being a familial disease (85.5%), and 84.7% of them expressed interest in genetic testing to determine cancer risk, 83.9% would have their fetuses tested for such cancer risk, 65.1% would terminate their pregnancies, 92.2% would have their children tested if they were determined to have an increased cancer risk, 71.9% would agree to undergo prophylactic oophorectomy or orchiectomy and 67.6% would have mastectomy/prostatectomy should there be an increased cancer risk to these organs. It appears that at least the sampled segment of a Turkish population is willing to undergo genetic testing to determine if they are at increased risk for cancer. The feasibility and acceptance of genetic testing and the influence of education and genetic counseling in the Turkish people should further be evaluated with a larger stratified sample of the population.     

Acquired and genetic susceptibility to cervical cancer

Infection with high-risk human papilloma virus (HPV) is a necessary risk factor for the development of cervical cancer (CC). However, there are many factors that contribute to the development of CC. We have been investigating the role of polymorphisms in chemical metabolizing genes and life-style factors in the development of CC between two countries with significantly different prevalence of CC. Our data confirm that infection with high-risk HPV is the most significant risk factor for CC in both Venezuela and US. In Venezuela, having multiple sex partners and early sexual activities are significant risk factors (OR=4.7, 95% CI=1.7-13.1; OR=6.7, 95% CI=2.3-20.1, respectively). On the other hand, cigarette smoking is the significant risk factor for women in the US (OR=6.4, 95% CI=1.8-23.2). Genotype analyses were conducted using specimens from the US population only. The GSTM1 null genotype was associated with a significant 3.4 fold increase in risk (95% CI=1.0-11.8) compared with those who were GSTM1 positive, after adjustment for smoking and HPV infection. Polymorphosis in CYP2E1 and mEH are associated with a non-significant increase in risk. Our study indicates that different acquired and genetic susceptibility factors can make significant contributions to the development of environmental disease such as cervical cancer.     

Factors associated with an individual's decision to withdraw from genetic testing for breast and ovarian cancer susceptibility: implications for counseling

Our study aimed to examine why individuals withdraw from genetic testing for breast and ovarian cancer susceptibility. We explored the characteristics of 334 individuals from high-risk breast and ovarian cancer families who declined genetic testing for BRCA1/2 mutations, when, and why they did so. Individuals who declined genetic testing were older, and a greater proportion had never developed breast or ovarian cancer. Fifty one per cent (51.1%) of individuals withdrew after the first genetic counseling session. Most of those who declined were afraid of the psychological effects of genetic testing (36.3%). The next most-cited explanations concerned logistic problems such as a limited ability to travel, lack of time, personal issues, advanced age, or health problems (21.7%). The third category included individuals who did not see any advantage in being tested (14.5%). Insurability was a concern (5.9%), mainly for men. Surprisingly, confidentiality was not a frequently reported issue (1.3%). Sixty eight per cent (68%) of individuals belonging to a family in which at least one individual has been tested withdrew after the presence of a deleterious BRCA1/2 mutation in a relative was disclosed, compared to 42% after the disclosure of a nonconclusive test result in at least one relative. Concern about the psychological effects of the result was still one of the major reasons. Several factors may influence an individual's decision to decline genetic testing; a greater understanding of these issues may help health professionals to better meet the needs and concerns of individuals from high-risk families, thus possibly improving their health outcomes.     

The role of test accuracy in predicting acceptance of genetic susceptibility testing for Alzheimer's disease

A survey questionnaire regarding perceptions of risk and genetic susceptibility to Alzheimer's disease (AD) was completed by 518 offspring of AD cases from families with multiple affected, ascertained as part of a genetic linkage study of late onset AD. The questionnaire focused on respondents' perceptions of their own risk for AD as well as on the properties of real and hypothetical susceptibility tests, including error rates for false-positive and false-negative test results. Our findings showed that about 20% of the sample would refuse a susceptibility test with zero error rates, about 40% would accept tests with very high error rates in both directions, and the remainder would exercise some discrimination. Acceptance of high test error rates was significantly associated with male gender, low education, and high perceived lifetime risk of AD. In a previous paper related to this work, we showed that physicians caring for these families exercised much more discrimination in judging the acceptability of genetic tests they would offer to these same respondents. The findings show that there is a pressing need to educate the public, particularly those with relatives affected by a complex disease, to expect standards of accuracy for genetic tests comparable to those that prevail in other diagnostic and prognostic testing efforts in the broad field of clinical medicine.     

Linkage analysis of 26 Canadian breast and breast-ovarian cancer families

We have examined 26 Canadian families with hereditary breast or ovarian cancer for linkage to markers flanking the BRCA1 gene on chromosome 17q12–q21. Of the 15 families that contain cases of ovarian cancer, 94% were estimated to be linked to BRCA1. In contrast, there was no overall evidence of linkage in the group of 10 families with breast cancer without ovarian cancer. A genetic recombinant in a breast-ovarian cancer family indicates a placement of BRCA1 telomeric to D17S776, and helps to define the region of assignment of the cancer susceptibility gene. Other cancers of interest that appeared in the BRCA1-linked families included primary peritoneal cancer, cancer of the fallopian tube, and malignant melanoma.     

Immunological and genetic factors influencing development and susceptibility to cancer

The results of a variety of studies on the genetic and immunological aspects of reproduction can be integrated into a hypothesis about the factors that regulate implantation and development and that may also cause an increased susceptibility to cancer. The primary condition for successful reproduction is genetic compatibility between the mating partners: there must be no recessive lethal genes that could act alone or epistatically to cause embryonic or fetal death. Such recessive lethal genes have been identified in the mouse (t-haplotypes) and in the rat (grc), and there is some evidence that they also exist in humans. Immunological factors may modulate the implantation of the fertilized ovum under some cireumstances after the genetic condition has been met. The same genetic factors that affect development may also affect susceptibility to cancer. This part of the hypothesis is supported by a number of clinical correlations between congenital defects and a higher incidence of cancer and by the demonstration of an increased susceptibility to the effects of chemical carcinogens in rats carrying the grc.     

Attitudes toward genetic testing for cancer risk after genetic counseling and decision support: a qualitative comparison between hereditary cancer types

This study aimed to qualitatively assess individuals' attitudes toward genetic testing for cancer risk after genetic counseling and decision support. As part of a larger study, 78 women considering genetic testing for hereditary breast/ovarian cancer (HBOC) risk and 22 individuals considering genetic testing for hereditary nonpolyposis colorectal cancer (HNPCC) completed an open-ended table of their perceived pros and cons of genetic testing. The most frequently reported pros were "to help manage my risk of developing cancer," "to help my family," and "to know my cancer risk." With regards to risk management, the HBOC group perceived genetic testing as most helpful in informing their general risk management practices, while the HN-PCC group focused on the potential to clarify their need for bowel cancer screening, suggesting that patients' perceptions of the benefits of genetic testing may differ across cancer syndromes. Individuals in both groups expressed concern about the potential psychological impact of genetic testing. We also found that some affected individuals may not fully comprehend the meaning of their potential test results. Eliciting patients' perceived pros and cons during genetic counseling is likely to be a valuable tool for improving patient care. This data also provides an improved evidence base for the development of patient education tools.     

Antifungal drug susceptibility testing

The advent of new antifungal drugs provides clinicians with therapeutic options, and it is anticipated requests for fungal susceptibility testing in vitro will increase. Our own laboratory's experience indicates that results can be provided promptly even to distant medical centers. The need in this setting is standardization of procedures, so correlations with in vivo outcome can be made with in vitro results. The variables affecting current testing methods are reviewed. Newer methods of testing are summarized, including our experiences using a spectrophotometer as a tool to assay inhibition. Our understanding of the mechanisms underlying the results with this and classical methods are presented. Several methods were applied to a population survey of Candida albicans isolates, using the drug flucytosine as an example. The results were correlated with in vivo outcome in a mouse model of systemic candidosis. The in vitro results, in general, predicted survival, but exceptions occurred, and it appears the in vitro results provide a relative but not absolute indication of outcome.     

Loss of heterozygosity studies in tumors from families with breast-ovarian cancer syndrome

A gene (BRCA1) predisposing for familial breast and ovarian cancer has been mapped to chromosome band 17q12-21. Based on the observation that ovarian tumors from families with breast and ovarian cancer lose the wild-type allele in the region for the BRCA1 locus, it has been suggested that the gene functions as a tumor suppressor gene. We have studied chromosomal deletions in the BRCA1 region in seven breast tumors, three ovarian tumors, one bladder cancer, and one colon cancer from patients in six families with breast-ovarian cancer, in order to test the hypothesis of the tumor suppressor mechanism at this locus. We have found a low frequency of loss of heterozygosity at this region, and our results do not support the idea that BRCA1 is a tumor suppressor gene. Alternatively, the disease segregating in these families is linked to one or more different loci.     

Evolution of testing strategies for genetic toxicity

Shortly following the inception of genetic toxicology as a distinct discipline within toxicology, questions arose regarding the type and number of tests needed to classify a chemical as a mutagenic hazard or as a potential carcinogen. To some degree the discipline separated into two sub-specialties, (1) genetic risk assessment and (2) cancer prediction since data from experimental oncology also supports the existence of a genotoxic step in tumor initiation. The issue of which and how many tests continued to be debated, but is now focused more tightly around two independent phenomena. Tier or sequential testing was initially proposed as a logical and cost-effective method, but was discarded on the basis that the lower tier tests appeared to have too many false responses to force or exclude further testing of the test agent. Matrix (battery) testing was proposed for screening on the hypothesis that combinations of endpoints and multiple phylogenetic target organisms were needed to achieve satisfactory predictability. As the results from short-term test 'validation' studies for carcinogen prediction and evaluations of EPA's Gene-Tox data accumulated, it became obvious that qualitative differences remained between predictive and definitive tests and by assembling different combinations of short-term assays investigators did not appear to resolve the lack of concordance. Recent trends in genetic toxicology testing have focused on mathematical models for test selection, and standardized systems for multi-test data assessment.