Publications by MACGN Members

Book

Prostate Cancer

Breast/Ovarian Cancer

Title:
Participation in Breast Cancer Susceptibility Testing Protocols: Influence of Recruitment Source, Altruism, and Family Involvement on Women's Decisions

Authors:
Geller G; Doksum T; Bernhardt BA; Metz SA

Source:
Cancer Epidemiol Biomarkers Prev 1999 Apr;8(4 Pt 2):377-83

Abstract:
OBJECTIVES: We offered education, counseling, and family-based BRCA1/2 testing to women at increased risk of breast cancer and assessed (a) their reasons for participating and (b) whether source of recruitment, desire to help research (altruism), and the need to communicate with their affected relative about testing distinguish those who did and those who did not complete each phase of our protocol. MATERIALS AND METHODS: We sent invitations to 403 women who had completed a questionnaire on BRCA1/2 testing, 178 of whom were considered high risk because they had more than one relative on the same side of the family with early-onset breast cancer. RESULTS: Among the 132 high-risk respondents from the mid-Atlantic states (where testing was offered), 36% (n = 47) were interested in counseling. Those who actually attended counseling were more likely to have some college education, a higher perceived risk of breast cancer, and a greater fear of stigma and were less likely to have a daughter than those who did not attend. The reasons for attending that were rated "very important" were to learn about the test (80%), to have the test (43%), and to help research (38%). High-risk women were eligible for testing only if their affected relative was willing to be tested and tested positive. After the session, 83% intended to ask their affected relative to be tested, but only half of the affected relatives actually came for pretest counseling. The proportion of participants who ultimately involved an affected relative was 2.5 times higher among women from a clinical population (25%) than among those from a registry population (10%); in this latter population, an altruistic desire to help research was a greater motivator for participation than interest in being tested. CONCLUSIONS: Source of recruitment influences both motivations to attend education and counseling and actual testing behavior. These results have implications for interpretation of findings from studies in research settings as well as for informed consent and decision- making in the context of family-based testing.

Title:
Epidemiology, prevention, and early detection of breast cancer

Authors:
Alberg AJ; Visvanathan K; Helzlsouer KJ

Source:
Curr Opin Oncol 1998 Nov;10(6):492-7

Abstract:
The evidence that alcohol consumption increases a woman's chances of getting breast cancer is now more persuasive. Higher blood concentrations of organochlorine compounds were not associated with increased risk of breast cancer in recent studies. The relationship of exogenous estrogen use to breast cancer risk is now clarified: current users of both oral contraceptives and hormone replacement therapy experience a slightly elevated risk that dissipates after cessation of use. Alcohol consumption and hormone replacement therapy are both associated with slightly increased breast cancer risk, but the overall health benefits of hormone replacement therapy and low levels of alcohol consumption appear to outweigh the risks in the general population. These circumstances underscore the complex decisions facing women and the need to consider individual risk factor profiles. For the genes BRCA1 and BRCA2, more data are needed to understand the risks associated with specific mutations, optimal implementation of genetic testing, and prevention and early detection strategies for women who have positive test results. Interesting leads in identifying women at increased risk for breast cancer have been generated via the study of genetic polymorphisms. The results of tamoxifen in the Breast Cancer Prevention Trial have made the possibility of chemoprevention for breast cancer a reality. Raloxifene, another antiestrogen, has emerged as a potential chemopreventive agent. Its efficacy in reducing breast cancer risk will be compared with that of tamoxifen in a randomized trial.

Title:
Association between CYP17 polymorphisms and the development of breast cancer

Authors:
Helzlsouer KJ; Huang HY; Strickland PT; Hoffman S; Alberg AJ; Comstock GW; Bell DA

Source:
Cancer Epidemiol Biomarkers Prev 1998 Oct;7(10):945-9

Abstract:
A nested case-control study was conducted to determine whether agenetic polymorphism in the CYP17 gene, which encodes for an enzyme that mediates steroid hormone metabolism, was associated with an increased risk of breast cancer. No association was found between the presence of an A2 allele and the subsequent development of breast cancer [A1/A2 odds ratio, 0.61 (95% confidence interval, 0.33-1.14); A2/A2 odds ratio, 0.89 (95% confidence interval, 0.41-1.95)]. No significant association was observed with risk factors presumed to be surrogates for endogenous estrogen exposure, nor was there an association observed with the stage of disease at diagnosis. Genotype frequencies in this Caucasian population were similar to those reported for African-American, Asian, and Latino women. Additional studies of larger size are needed to achieve a consensus regarding the relevance of CYP17 genotypes to the risk of developing breast cancer.

Title:
Decision-making about breast cancer susceptibility testing: how similar are the attitudes of physicians, nurse practitioners, and at-risk women?

Authors:
Geller G; Bernhardt BA; Doksum T; Helzlsouer KJ; Wilcox P; Holtzman NA

Source:
J Clin Oncol 1998 Aug;16(8):2868-76

Abstract:
PURPOSE: To determine what consumers and providers would want to discuss about breast cancer susceptibility testing (BCST) and their preferred role in testing decisions. METHODS: We surveyed 426 at-risk women, 143 nurse practitioners, and 296 physicians in five specialties in Maryland. RESULTS: All groups believe it is important to discuss how the chance of breast cancer can be reduced and what the chances are of getting breast cancer if the test is positive. Both provider groups attributed more importance than consumers to discussing whether cancer can occur if the test is negative. Discussing the risk of depression and anxiety was more important to providers than consumers. Eighty-two percent of women would want their providers to make a recommendation about testing, but only 43% of nurse practitioners and 68% of physicians would do so. Eighteen percent of physicians underestimated the importance of informed consent for testing and 34% of discussing the risk of insurance discrimination. Fewer than 6% of women, if found to have a mutation, would be likely to undergo prophylactic mastectomy, whereas 12% of nurse practitioners and 34% of physicians would be likely to recommend such surgery. One third of respondents in all three groups supported testing a 13-year old daughter of a mutation-carrier. CONCLUSION: Physicians should place greater value on informed consent and discussing practical aspects of testing, and physicians and nurse practitioners should pay more attention to the limitations of testing children, insurance discrimination, and consumers' desire for provider recommendations. In light of the limited discordance between nurse practitioners and consumers, nurse practitioners can play an increasing role in education and counseling about BCST.

Title:
Association between glutathione S-transferase M1, P1, and T1 genetic polymorphisms and development of breast cancer

Authors:
Helzlsouer KJ; Selmin O; Huang HY; Strickland PT; Hoffman S; Alberg AJ; Watson M; Comstock GW; Bell D

Source:
J Natl Cancer Inst 1998 Apr 1;90(7):512-8 [comment]

Abstract:
BACKGROUND: Glutathione S-transferases (GSTs) are encoded by a superfamily of genes and play a role in the detoxification of potential carcinogens. In a nested case-control study, we investigated associations between genetic variability in specific GST genes (GSTM1, GSTT1, and GSTP1) and susceptibility to breast cancer. METHODS: In 1989, a total of 32 898 individuals donated blood samples to a research specimen bank established in Washington County, MD. Genotypes of blood specimen DNA were determined for 110 of 115 women with incident cases of breast cancer diagnosed during the period from 1990 through 1995 and up to 113 of 115 control subjects. Associations between specific genotypes and the development of breast cancer were examined by use of logistic regression to calculate odds ratios (ORs) and 95% confidence intervals (CIs). RESULTS: The GSTM1 homozygous null genotype was associated with an increased risk of developing breast cancer (OR = 2.10; 95% CI = 1.22-3.64), principally due to an association with postmenopausal breast cancer (OR = 2.50; 95% CI = 1.34-4.65). For GSTP1, the data were suggestive of a trend of increasing risk with higher numbers of codon 105 valine alleles (compared with isoleucine alleles); a 1.97-fold increased risk of breast cancer (95% CI = 0.77- 5.02) was associated with valine/valine homozygosity. The risk of breast cancer associated with the GSTT1 homozygous null genotype was 1.50 (95 % CI = 0.76-2.95). The risk of breast cancer increased as the number of putative high-risk genotypes increased (P for trend < .001) (OR = 3.77; 95% CI = 1.10-12.88 for a combined genotype of GSTM1 null, GSTT1 null, and either GSTP1 valine heterozygosity or GSTP1 valine homozygosity). CONCLUSIONS: Our findings suggest that genetic variability in members of the GST gene family may be associated with an increased susceptibility to breast cancer.

Colorectal Cancer

Title:
Attitudes Toward Colon Cancer Gene Testing: Survey of Relatives of Colon Cancer Patients

Authors:
Petersen GM; Larkin E; Codori AM; Wang CY; Booker SV; Bacon J; Giardiello FM; Boyd PA

Source:
Cancer Epidemiol Biomarkers Prev 1999 Apr;8(4 Pt 2):337-44

Abstract:
OBJECTIVES: Various studies have identified psychosocial factors that may influence attitudes toward colon cancer gene testing. Whereas family history of colon cancer has been associated with interest in gene testing, this has not been examined extensively. We hypothesized that the strength of family history of colon cancer is associated with risk perception and willingness to undergo gene testing. MATERIALS AND METHODS: We evaluated attitudes toward colon cancer gene testing among persons who had at least one first-degree relative with colon cancer. A total of 2680 at-risk relatives in 863 kindreds were identified and mailed an extensive survey regarding sociodemographic variables, family history, health behaviors and knowledge, and willingness to take a colon cancer gene test. A total of 56.6% of persons completed and returned surveys. We conducted a brief telephone survey of a random sample of 200 persons who did not respond to the mail survey. RESULTS: The combined study sample of 1373 people was 42% male, had a mean age of 55 +/- 15 years, was 96% white, and had moderate-to-high SES. A total of 77.4% were very likely to take the gene test, and 92.4% were somewhat or very likely to take the gene test. A total of 78% of the sample perceived a higher colon cancer risk, although patterns of risk perception and worry differed significantly between mail survey and telephone survey respondents. More of the telephone survey respondents were also somewhat unlikely or very unlikely to take the gene test compared to the mail survey respondents (13.7% versus 6.9%). In the combined sample, concern about developing colon cancer and risk perception increased with number of relatives with colon cancer (P < 0.0001). Eight percent expressed no concern about developing colon cancer; 4.8% felt their chance of developing colon cancer was lower than others of the same age, sex, and race; and 3.3% felt that they were very unlikely to develop colon cancer in their lifetime. However, there was strong interest in gene testing regardless of the number of affected relatives, and persons with more affected relatives were generally willing to pay more for the gene test (up to $1000). CONCLUSIONS: The strength of family history of colon cancer is associated with risk perception but not with willingness to undergo gene testing.

Title:
Attitudes Toward Colon Cancer Gene Testing: Factors Predicting Test Uptake

Authors:
Codori AM; Petersen GM; Miglioretti DL; Larkin EK; Bushey MT; Young C; Brensinger JD; Johnson K; Bacon JA; Booker SV

Source:
Cancer Epidemiol Biomarkers Prev 1999 Apr;8(4 Pt 2):345-51

Abstract:
OBJECTIVES: Genetic discoveries in hereditary nonpolyposis colorectal cancer (HNPCC) have made possible genetic testing to determine susceptibility to this form of colorectal cancer (CRC). This study measured the uptake of genetic testing for HNPCC among first-degree relatives of CRC patients and conducted a preliminary analysis of the predictors of test uptake. MATERIALS AND METHODS: We compared 77 test acceptors and 181 decliners on demographic, medical history, and psychological characteristics, controlling for distance from the testing center. The psychological factors studied were risk perception for CRC, frequency of cancer thoughts, and perceived ability to cope with unfavorable genetic information. RESULTS: In the final regression model, after accounting for all variables, the significant predictors of test uptake were increased risk perception, greater perceived confidence in ability to cope with unfavorable genetic information, more frequent cancer thoughts, and having had at least one colonoscopy. The association between risk perception and uptake was dependent on frequency of cancer thoughts. Among those who thought about getting CRC more often, the probability of testing increased as perceived risk increased to approximately 50% likelihood of getting CRC and then leveled off. In contrast, among those who never or rarely thought about getting CRC, risk perception was unrelated to testing decision. CONCLUSIONS: Our findings are consistent with the associations reported between psychological factors and other cancer screening behaviors.

Title:
Analysis of masked mutations in familial adenomatous polyposis

Authors:
Laken SJ; Papadopoulos N; Petersen GM; Gruber SB; Hamilton SR; Giardiello FM; Brensinger JD; Vogelstein B; Kinzler KW

Source:
Proc Natl Acad Sci U S A 1999 Mar 2;96(5):2322-6

Abstract:
Familial adenomatous polyposis (FAP) is an autosomal-dominant disease characterized by the development of hundreds of adenomatous polyps of the colorectum. Approximately 80% of FAP patients can be shown to have truncating mutations of the APC gene. To determine the cause of FAP in the other 20% of patients, MAMA (monoallelic mutation analysis) was used to independently examine the status of each of the two APC alleles. Seven of nine patients analyzed were found to have significantly reduced expression from one of their two alleles whereas two patients were found to have full-length expression from both alleles. We conclude that more than 95% of patients with FAP have inactivating mutations in APC and that a combination of MAMA and standard genetic tests will identify APC abnormalities in the vast majority of such patients. That no APC expression from the mutant allele is found in some FAP patients argues strongly against the requirement for dominant negative effects of APC mutations. The results also suggest that there may be at least one additional gene, besides APC, that can give rise to FAP.

Title:
Pathogenesis of Adenocarcinoma in Peutz-Jeghers Syndrome

Authors:
Gruber SB; Entius MM; Petersen GM; Laken SJ; Longo PA; Boyer R; Levin AM; Mujumdar UJ; Trent JM; Kinzler KW; Vogelstein B; Hamilton SR; Polymeropoulos MH; Offerhaus GJ; Giardiello FM

Source:
Cancer Res 1998 Dec 1;58(23):5267-70

Abstract:
Peutz-Jeghers syndrome (PJS) is an autosomal dominant condition characterized by intestinal hamartomatous polyps, mucocutaneous melanin deposition, and increased risk of cancer. Families with PJS from the Johns Hopkins Polyposis Registry were studied to identify the molecular basis of this syndrome and to characterize the pathogenesis of gastrointestinal hamartomas and adenocarcinomas in PJS patients. Linkage analysis in the family originally described by Jeghers in 1949 and five other families confirmed linkage to 19p13.3 near a recently identified gene responsible for PJS. Germ-line mutations in this gene, STK11, were identified in all six families by sequencing genomic DNA. Analysis of hamartomas and adenocarcinomas from patients with PJS identified loss of heterozygosity (LOH) of 19p markers near STK11 in 70% of tumors. Haplotype analysis indicated that the retained allele carried a germ-line mutation, confirming that STK11 is a tumor suppressor gene. LOH of 17p and 18q was identified in an adenocarcinoma but not in hamartomas, implying that allelic loss of these two regions corresponds to late molecular events in the pathogenesis of cancer in PJS. The adenocarcinomas showing 17p LOH also demonstrated altered p53 by immunohistochemistry. None of the 18 PJS tumors showed microsatellite instability, LOH on 5q near APC, or mutations in codons 12 or 13 of the K-ras proto-oncogene. These data provide evidence that STK11 is a tumor suppressor gene that acts as an early gatekeeper regulating the development of hamartomas in PJS and suggest that hamartomas may be pathogenetic precursors of adenocarcinoma. Additional somatic mutational events underlie the progression of hamartomas to adenocarcinomas, and some of these somatic mutations are common to the later stages of tumor progression seen in the majority of colorectal carcinomas.

Title:
Variable phenotype of familial adenomatous polyposis in pedigrees with 3' mutation in the APC gene

Authors:
Brensinger JD; Laken SJ; Luce MC; Powell SM; Vance GH; Ahnen DJ; Petersen GM; Hamilton SR; Giardiello FM

Source:
Gut 1998 Oct;43(4):548-52 [Comment]

Abstract:
BACKGROUND: Germline mutation in the adenomatous polyposis coli (APC) gene on chromosome 5 causes familial adenomatous polyposis. "Attenuated" phenotype has been reported with mutation in the 5' end of the gene (5' to codon 158), but genotype-phenotype relations at the 3' end (3' to codon 1596) have not been described fully. AIMS: To describe and compare colorectal and extracolonic phenotypes in a case series of families with mutation in the 3' end of the APC gene. METHODS: Thirty one at risk or affected members from four families with a mutation in the APC gene located at codon 1979 or 2644 were evaluated. RESULTS: Variable intrapedigree colorectal phenotype was observed: some members at older age had oligopolyposis (fewer than one hundred colorectal adenomas) whereas other members had classic polyposis at young age. Colorectal cancer was diagnosed at older mean age (50 (7) years) in the four families than in classic FAP pedigrees (39 (14) years). Extracolonic lesions characteristic of FAP occurred with 3' APC mutations, but variability in intrapedigree and interpedigree extracolonic phenotype and dissociation of severity of extracolonic manifestations from number of colorectal polyps was noted. CONCLUSIONS: Families with 3' mutations of the APC gene exhibit variable intrapedigree phenotype similar to the heterogeneity noted in families with proximal 5' mutations. Genotyping of FAP and oligopolyposis pedigrees can guide appropriate surveillance of the upper and lower gastrointestinal tract in affected members.

Title:
Missense mutations in disease genes: a Bayesian approach to evaluate causality

Authors:
Petersen GM; Parmigiani G; Thomas D

Source:
Am J Hum Genet 1998 Jun;62(6):1516-24

Abstract:
The problem of interpreting missense mutations of disease-causing genes is an increasingly important one. Because these point mutations result in alteration of only a single amino acid of the protein product, it is often unclear whether this change alone is sufficient to cause disease. We propose a Bayesian approach that utilizes genetic information on affected relatives in families ascertained through known missense- mutation carriers. This method is useful in evaluating known disease genes for common disease phenotypes, such as breast cancer or colorectal cancer. The posterior probability that a missense mutation is disease causing is conditioned on the relationship of the relatives to the proband, the population frequency of the mutation, and the phenocopy rate of the disease. The approach is demonstrated in two cancer data sets: BRCA1 R841W and APC I1307K. In both examples, this method helps establish that these mutations are likely to be disease causing, with Bayes factors in favor of causality of 5.09 and 66.97, respectively, and posterior probabilities of .836 and .985. We also develop a simple approximation for rare alleles and consider the case of unknown penetrance and allele frequency.

Title:
Cost analysis of alternative approaches to colorectal screening in familial adenomatous polyposis.

Authors:
Cromwell DM; Moore RD; Brensinger JD; Petersen GM; Bass EB; Giardiello FM

Source:
Gastroenterology 1998 May;114(5):893-901

Abstract:
BACKGROUND & AIMS: The commercial availability of gene testing for familial adenomatous polyposis (FAP) represents an important advance in screening for inherited colon cancer. We investigated the financial impact of this diagnostic tool on colorectal screening for FAP. METHODS: Decision analysis was used to compare per-person costs with third-party payers of three colorectal screening strategies used to diagnose FAP in at-risk persons. The strategies included conventional serial flexible sigmoidoscopy and two different APC gene testing approaches. RESULTS: For 1 at-risk relative who begins screening at age 12 years, average screening costs are $2625 when genotyping the proband first, $2674 when genotyping the at-risk relative first, and $3208 for conventional sigmoidoscopy. The cost advantage of genotyping increases as the pedigree size increases. For a pedigree of 5 at-risk relatives, sigmoidoscopy would have to cost less than $85.60 (professional plus facility fee) for conventional screening to compete with genotyping. The cost advantage of genotyping is diminished for at-risk relatives who begin FAP screening at older ages. CONCLUSIONS: The choice of least expensive FAP screening strategy depends on the cost of flexible sigmoidoscopy, patient age when screening starts, and pedigree size. Genotyping can substantially reduce the cost of FAP screening and, when possible, should start with the proband.

Title:
Landscaping the cancer terrain

Authors:
Kinzler KW; Vogelstein B

Source:
Science 1998 May 15;280(5366):1036-7

Abstract:
Comment, no abstract available.

Title:
Size-dependent increase in prostanoid levels in adenomas of patients with familial adenomatous polyposis

Authors:
Yang VW; Shields JM; Hamilton SR; Spannhake EW; Hubbard WC; Hylind LM; Robinson CR; Giardiello FM

Source:
Cancer Res 1998 Apr 15;58(8):1750-3

Abstract:
Recent studies indicate that nonsteroidal anti-inflammatory drugs have a chemopreventive effect against colorectal neoplasia. Nonsteroidal anti-inflammatory drugs inhibit cyclooxygenases, principal enzymes that mediate the formation of prostanoids. To determine whether prostanoids are involved in the pathogenesis of colorectal adenomas, we compared the levels of five major stable metabolic products of the cyclooxygenase pathway in the normal-appearing mucosa and in adenomas of patients with familial adenomatosis polyposis. Of 12 patients tested, 6 had elevated levels of at least one prostanoid in the adenomas. More importantly, the relative levels of three prostanoids [prostaglandin (PG)D2, PGE2, and 6-keto-PGF1alpha] were elevated in adenomas compared to normal-appearing mucosa from the same patients, and the resulting ratios were correlated with the size of the adenoma. These results suggest a role for prostanoids in progression of colorectal polyposis in familial adenomatosis polyposis patients.

Title:
Prostaglandin levels in human colorectal mucosa: effects of sulindac in patients with familial adenomatous polyposis

Authors:
Giardiello FM; Spannhake EW; DuBois RN; Hylind LM; Robinson CR; Hubbard WC; Hamilton SR; Yang VW

Source:
Dig Dis Sci 1998 Feb;43(2):311-6

Abstract:
Recent evidence suggests that nonsteroidal antiinflammatory drugs (NSAIDs) may prevent colorectal cancer. The mechanism of action of NSAIDs in chemoprevention is unknown but may be linked to their effect on mucosal prostaglandin levels. Levels of five major prostaglandin metabolites were measured by gas chromatography-mass spectrometry in biopsy specimens of flat rectal mucosa from four patients with familial adenomatous polyposis (FAP) before and after sulindac therapy and from five healthy individuals. The prostaglandin present at highest concentration in rectal mucosa from FAP and control subjects was prostaglandin E2. The concentration of thromboxane B2 alone was significantly elevated in FAP patients compared to controls (P = 0.016). In FAP patients treated with sulindac, all prostaglandin metabolite levels were significantly reduced compared to pretreatment levels (P < 0.05) except prostaglandin D2 (P = 0.07). Prostaglandins D2, E2, F2alpha, and 6-keto-F1alpha levels also were significantly reduced in FAP patients on sulindac compared to healthy controls (P < 0.05). However, interpatient heterogeneity of response to sulindac was evident with changes ranging from +19% to -89%, and the patient with the greatest reductions after sulindac developed colorectal cancer after 35 months of therapy. Sulindac treatment, at drug doses shown to regress colorectal adenomas in FAP patients, has heterogeneous effects on the level of major prostaglandins in their rectal mucosa and may not prevent colorectal cancer due to uncoupling of prostaglandin levels and carcinogenesis.

Title:
Familial colorectal cancer in Ashkenazim due to a hypermutable tract in APC

Authors:
Laken SJ; Petersen GM; Gruber SB; Oddoux C; Ostrer H; Giardiello FM; Hamilton SR; Hampel H; Markowitz A; Klimstra D; Jhanwar S; Winawer S; Offit K; Luce MC; Kinzler KW; Vogelstein B

Source:
Nat Genet 1997 Sep;17(1):79-83

Abstract:
Approximately 130,000 cases of colorectal cancer (CRC) are diagnosed in the United States each year, and about 15% of these have a hereditary component. Two well-defined syndromes, familial adenomatous polyposis (FAP) and hereditary non-polyposis colorectal cancer (HNPCC), account for up to 5% of the total new cases of CRC. Truncating APC mutations are responsible for FAP, and defective mismatch repair genes cause HNPCC. However, the genes responsible for most of the familial cases are unknown. Here we report a mutation (T to A at APC nucleotide 3920) found in 6% of Ashkenazi Jews and about 28% of Ashkenazim with a family history of CRC. Rather than altering the function of the encoded protein, this mutation creates a small hypermutable region of the gene, indirectly causing cancer predisposition.

Prostate Cancer

Title:
Evidence for a prostate cancer susceptibility locus on the X chromosome

Authors:
Xu J; Meyers D; Freije D; Isaacs S; Wiley K; Nusskern D; Ewing C; Wilkens E; Bujnovszky P; Bova GS; Walsh P; Isaacs W; Schleutker J; Matikainen M; Tammela T; Visakorpi T; Kallioniemi OP; Berry R; Schaid D; French A; McDonnell S; Schroeder J; Blute M; Thibodeau S; Trent J; et al

Source:
Nat Genet 1998 Oct;20(2):175-9

Abstract:
Over 200,000 new prostate cancer cases are diagnosed in the United States each year, accounting for more than 35% of all cancer cases affecting men, and resulting in 40,000 deaths annually. Attempts to characterize genes predisposing to prostate cancer have been hampered by a high phenocopy rate, the late age of onset of the disease and, in the absence of distinguishing clinical features, the inability to stratify patients into subgroups relative to suspected genetic locus heterogeneity. We previously performed a genome-wide search for hereditary prostate cancer (HPC) genes, finding evidence of a prostate cancer susceptibility locus on chromosome 1 (termed HPC1; ref. 2). Here we present evidence for the location of a second prostate cancer susceptibility gene, which by heterogeneity estimates accounts for approximately 16% of HPC cases. This HPC locus resides on the X chromosome (Xq27-28), a finding consistent with results of previous population-based studies suggesting an X-linked mode of HPC inheritance. Linkage to Xq27-28 was observed in a combined study population of 360 prostate cancer families collected at four independent sites in North America, Finland and Sweden. A maximum two-point lod score of 4.60 was observed at DXS1113, theta=0.26, in the combined data set. Parametric multipoint and non-parametric analyses provided results consistent with the two-point analysis. Significant evidence for genetic locus heterogeneity was observed, with similar estimates of the proportion of linked families in each separate family collection. Genetic mapping of the locus represents an important initial step in the identification of an X-linked gene implicated in the aetiology of HPC.