A polymorphism in the CDKN1B gene is associated with increased risk of hereditary prostate cancer

The loss of cell cycle control is believed to be an important mechanism in the promotion of carcinogenesis. CDKN1B (p27) belongs to the Cip/Kip family and functions as an important cell cycle gatekeeper. Several lines of evidence from clinical studies and laboratory experiments demonstrate that CDKN1B is an important tumor suppressor gene in prostate cancer etiology. In addition, a case-control study has shown that the 326T/G (V109G) polymorphism in CDKN1B is associated with advanced prostate cancer. In light of the evidence for linkage between the chromosomal location of the CDKN1B gene (12p13) and prostate cancer susceptibility in several hereditary prostate cancer (HPC) populations, we hypothesized that sequence variants of CDKN1B play a role in HPC. To test this hypothesis, we first resequenced this gene in 96 HPC probands to identify germ-line mutations and sequence variants. We then genotyped the identified sequence variants among all family members of 188 HPC families and tested for their cosegregation with prostate cancer. In total, 10 sequence variants were identified, including three nonsynonymous changes. A family-based test, which is free from the effects of population stratification, revealed a significant association between single nucleotide polymorphism (SNP) -79C/T and prostate cancer (with a nominal P of 0.0005). The C allele of -79C/T was overtransmitted from parents to their affected offspring. Evidence for this association was primarily contributed by affected offspring whose age at diagnosis was <65 years. Together with the previous association study in a sporadic prostate cancer population, our new findings additionally suggest that germ-line variants of this gene play a role in prostate cancer susceptibility.     

Cytochrome P450 1B1 polymorphisms and risk of renal cell carcinoma in men

The cytochrome P450 1B1 (CYP1B1) enzyme activates xenobiotics to reactive forms as well as convert estradiol to 4-hydroxy-estradiol that has been shown to play a role in the carcinogenesis process of the kidney in male but not female animals. Prior reports show polymorphic variants of CYP1B1 to alter catalytic activity, and thus, we hypothesize that polymorphisms of the CYP1B1 gene are involved in the malignant transformation of the renal cell in men. The genetic distributions of five CYP1B1 polymorphisms were analyzed by polymerase chain reaction–restriction fragment length polymorphism in 480 normal healthy subjects and 403 sporadic renal cell carcinoma cases. All subjects were Caucasian men. The sites evaluated were codons 48 (C?→?G, Arg?→?Gly, rs10012), 119 (G?→?T, Ala?→?Ser, rs1056827), 432 (C?→?G, Leu?→?Val, rs1056836), 449 (C?→?T, Asp, rs1056837), and 453 (A?→?G, Asn?→?Ser, rs1800440). A trend was demonstrated for the 432 Val/Val (χ2, P?=?0.06) and 449 T/T (χ2, P?=?0.1) genotypes to play a protective role against renal cancer. Odds ratio (95 % confidence interval) for Val/Val compared to Leu/Leu at codon 432 was 0.65 (0.44–0.95) and T/T compared to C/C at codon 449 was 0.67 (0.45–0.99). Codons 432 and 449 were observed to be linked (D?=?0.24), and haplotype involving 432 Val and 449 T was significantly reduced in cancer cases (P?=?0.04). No association was found, however, when analyzing polymorphic sites with clinical stage of cancer. These results demonstrate polymorphisms of CYP1B1 to be associated with renal carcinogenesis and are of importance in understanding their role in the pathogenesis of renal cell carcinoma.     

Variant genotypes of CDKN1A and CDKN1B are associated with an increased risk of breast cancer in Chinese women

p21(Cip1) and p27(Kip1) are cyclin-dependent kinase inhibitors, which can arrest cell proliferation and serve as tumor suppressors. Reduced protein expression of p21(Cip1) and p27(Kip1) was frequently observed in a subset of cancers, including breast cancer. In this study, we hypothesized that genetic variants in CDKN1A (encode for p21(Cip1)) and CDKN1B (encode for p27(Kip1)) may modulate the risk of breast cancer. To test this hypothesis, we evaluated the associations of the polymorphisms of Ser31Arg and C+20T in CDKN1A and C-79T and Gly109Val in CDKN1B, as well as their combinations, with breast cancer risk in a case-control study of 368 breast cancer cases and 467 cancer-free controls in a Chinese population. We found that a significantly increased risk of breast cancer was associated with the variant genotypes of CDKN1B C-79T [adjusted OR = 1.43 (95% CI = 1.03-1.98) for -79TC/TT], compared with the -79CC genotype, but no associations were observed for other variant genotypes. However, the combined variant genotypes of the 4 loci were associated with a significantly increased breast cancer risk (adjusted OR = 1.49, 95% CI = 1.11-2.01 among subjects carrying 3 or more variant alleles), especially among premenopausal women (adjusted OR= 2.30, 95% CI = 1.45-3.66). Furthermore, in premenopausal women, this significant association remained unchanged, after including other individual risk factors in the multivariate logistic regression model, suggesting an independent role of CDKN1A and CDKN1B variants in breast cancer risk. Although the exact biological mechanism remains to be explored, our findings suggest possible involvement of CDKN1A and CDKN1B variants in the etiology of breast cancer. Further large and functional studies are needed to confirm our findings.     

Cytochrome P450 1A1 genetic polymorphisms and risk of hepatocellular carcinoma among chronic hepatitis B carriers.

Cigarette smoking has been associated with increased risk of hepatocellular carcinoma (HCC) in some epidemiological studies. Cytochrome P450 1A1 (CYP1A1) is involved in the biotransformation of tobacco-derived polycyclic aromatic hydrocarbons (PAHs) into carcinogenic metabolites. The aim of this study was to determine whether CYP1A1 polymorphisms were related to HCC risk among chronic hepatitis B virus (HBV) carriers. Genotypic variants of CYP1A1 were determined using polymerase chain reaction in 81 incident cases of HCC and 409 controls nested in a cohort study of 4841 male chronic HBV carriers. No overall association between CYP1A1 genotypes and HCC was observed. The presence of the Mspl (odds ratio (OR) 3.15, P = 0.0196) or Ile-Val (OR 1.99, P = 0.0855) variant allele of CYP1A1 increased HCC risk among smokers, but posed no increased risk among non-smokers. The smoking-related HCC risk was most pronounced among those who had a susceptible allele of the CYP1A1 and a deficient genotype of glutathione S-transferase M1, which detoxifies PAH electrophilic metabolites produced by CYP1A1. In the absence of the Ile-Val variant allele, the Mspl polymorphism was still associated with smoking-related HCC. This study suggests that tobacco-derived PAHs play a role in HCC risk among chronic HBV carriers, and CYP1A1 polymorphism is an important modulator of the hepatocarcinogenic effect of PAHs. The Mspl and Ile-Val polymorphisms of CYP1A1 may have different mechanisms for increasing susceptibility to smoking-related HCC.     

IL-1B基因多态性与胃癌易感相关性研究

目的:探讨河南地区汉族人白细胞介素(IL)-1B基因多态性与胃癌的相关性以及是否与胃癌组织学分型相关联.方法: 采用聚合酶链反应-单链构象多态性技术(PCR-SSCP)和琼脂糖凝胶电泳(AGE)检测了220例对照和452例胃癌患者(肠型176例,弥散型137例,萎缩型139例)的IL-1B-511C/T基因位点.结果: IL-1B-511C等位基因频率在正常人群和胃癌组患者分别为0.82和0.76,IL-1B-511T 等位基因频率分别为0.18和0.24,两者差异有统计学意义.IL-1B-511T纯合子、携带者患肠型胃癌风险的OR分别为2.7(95% CI:1.5～4.9)和3.1(95% CI:1.5～6.5);T等位基因与肠型胃癌易感密切关联,与萎缩型胃癌易感差异无统计学意义,P＞0.05.结论: IL-1B-511C/T基因多态性与胃癌发生风险密切关联,T等位基因可能是肠型胃癌的易感标志.     

MiR-221 controls CDKN1C/p57 and CDKN1B/p27 expression in human hepatocellular carcinoma

The identification of target mRNAs is a key step for assessing the role of aberrantly expressed microRNAs in human cancer. MiR-221 is upregulated in human hepatocellular carcinoma (HCC) as well as in other malignancies. One proven target of miR-221 is CDKN1B/p27, whose downregulation affects HCC prognosis. Here, we proved that the cyclin-dependent kinase inhibitor (CDKI) CDKN1C/p57 is also a direct target of miR-221. Indeed, downregulation of both CDKN1B/p27 and CDKN1C/p57 occurs in response to miR-221 transfection into HCC-derived cells and a significant upregulation of both CDKN1B/p27 and CDKN1C/p57 occurs in response to antimiR-221 transfection. A direct interaction of miR-221 with a target site on the 3' UTR of CDKN1C/p57 mRNA was also demonstrated. By controlling these two CDKIs, upregulation of miR-221 can promote growth of HCC cells by increasing the number of cells in S-phase. To assess the relevance of these studies in primary tumors, matched HCC and cirrhosis samples were assayed for miR-221, for CDKN1B/p27 and CDKN1C/p57 expression. MiR-221 was upregulated in 71% of HCCs, whereas CDKN1B/p27 and CDKN1C/p57 proteins were downregulated in 77% of cases. A significant inverse correlation between miR-221 and both CDKN1B/p27 and CDKN1C/p57 was found in HCCs. In conclusion, we suggest that miR-221 has an oncogenic function in hepatocarcinogenesis by targeting CDKN1B/p27 and CDKN1C/p57, hence promoting proliferation by controlling cell-cycle inhibitors. These findings establish a basis toward the development of therapeutic strategies aimed at blocking miR-221 in HCC.     

Sun exposure, vitamin D receptor gene polymorphisms, and risk of advanced prostate cancer

Substantial experimental evidence indicates that the hormonal form of vitamin D promotes the differentiation and inhibits the proliferation, invasiveness, and metastasis of human prostatic cancer cells. Results from epidemiologic studies of vitamin D status and/or vitamin D receptor (VDR) polymorphisms and prostate cancer risk have been mixed. We conducted a population-based, case-control study of advanced prostate cancer among men ages 40 to 79 years from the San Francisco Bay area. Interview data on lifetime sun exposure and other risk factors were collected for 905 non-Hispanic White men (450 cases and 455 controls). Using a reflectometer, we measured constitutive skin pigmentation on the upper underarm (a sun-protected site) and facultative pigmentation on the forehead (a sun-exposed site) and calculated a sun exposure index from these measurements. Biospecimens were collected for 426 cases and 440 controls. Genotyping was done for VDR polymorphisms in the 5' regulatory region (Cdx-2), exon 2 (FokI), and the 3' region (TaqI and BglI). Reduced risk of advanced prostate cancer was associated with high sun exposure determined by reflectometry [odds ratio (OR), 0.51; 95% confidence interval (95% CI), 0.33-0.80] and high occupational outdoor activity (OR, 0.73; 95% CI, 0.48-1.11). Significant risk reductions with the high-activity alleles FokI FF or Ff, TaqI tt, and BglI BB genotypes and a nonsignificant reduction with Cdx-2 AG or AA genotype were observed in the presence of high sun exposure, with ORs ranging from 0.46 to 0.67. Our findings support the hypothesis that sun exposure and VDR polymorphisms together play important roles in the etiology of prostate cancer.     

Quantitative assessment of the influence of CYP1B1 polymorphisms and head and neck squamous cell carcinoma risk

The associations between CYP1B1 polymorphisms and head and neck squamous cell carcinoma (HNSCC) risk have been conflicting. We therefore performed a meta-analysis to derive a more precise relationship. Six published case–control studies were collected; odds ratios (ORs) with 95 % confidence interval (CI) were used to assess the association between CYP1B1 Leu432Val, Asn453Ser polymorphisms, and HNSCC risk. The Sensitivity analysis and publication bias also were performed to guarantee the statistical power. Overall, the pooled OR with 95 % CIs indicated that CYP1B1 Leu432Val polymorphism was significantly related with HNSCC risk (for Val vs. Leu: OR = 1.13, 95 % CI = 1.03–1.25, P?=?0.014, P _{heterogeneity}?=?0.141; for Val/Val vs. Leu/Leu: OR = 1.30, 95 % CI = 1.06–1.60, P?=?0.013, P _{heterogeneity}?=?0.253; for Val/Val vs. Leu/Leu + Leu/Val: OR = 1.23, 95 % CI = 1.05–1.46, P?=?0.013, P _{heterogeneity}?=?0.456). The similar results were also been found in succeeding analysis of HWE and stratified analysis of Caucasian population. Furthermore, no significant association between CYP1B1 Asn453Ser polymorphism and HNSCC risk was found in this meta-analysis. In conclusion, our meta-analysis demonstrates that CYP1B1 Leu432Val polymorphism may be a risk factor for developing HNSCC.     

Association of CYP1B1 polymorphisms and breast cancer risk.

Cytochrome P450 1B1 catalyzes the conversion of 17-beta-estradiol (E2) to thecatechol estrogen metabolites 2-OH-E2 and 4-OH-E2 that have been postulated to be involved in mammary carcinogenesis. We sought to determine whether two common functional polymorphisms in Cytochrome P450 1B1, V432L (m1), and A453S (m2) are related to breast cancer risk. Using a nested case control design within the Nurses' Health Study cohort, we genotyped 453 cases and 456 controls and found no significant association between m1[val/leu and leu/leu versus val/val, OR = 1 (CI, 0.72-1.45)] or m2 [asn/ser and ser/ser versus asn/asn, OR = 0.8 (CI, 0.62-1.15)] and breast cancer risk. However, we did observe women with the Val/Val (m1) genotype to have a higher percentage of estrogen receptor-positive tumors (P = 0.03). We did not observe any correlation with the m2 genotypes and estrogen receptor status. The association of the m1 and m2 genotypes on plasma hormone levels in postmenopausal control women not using hormone replacement therapy was also evaluated. Carriers of the m1 leu and m2 ser alleles had modestly higher estradiol levels but similar estrone and estrone sulfate levels. The results presented do not support a strong association between m1 and m2 and the risk of breast cancer.     

Genetic polymorphisms of interleukin-1B (IL-1B), IL-6, IL-8, and IL-10 and risk of prostate cancer

Chronic intraprostatic inflammation is suspected to play a role in the pathogenesis of prostate cancer. Polymorphisms in cytokine genes can influence inflammation and immune response and may be related to the risk of prostate cancer. Four common single nucleotide polymorphisms (SNPs) in the genes encoding interleukin-1B (IL-1B), IL-6, and IL-8 were assessed in 503 prostate cancer cases and 652 controls, and three SNPs in IL-10 were assessed in an additional 817 prostate cancer cases and 1,190 controls (for a total of 1,320 prostate cancer cases and 1,255 controls). Cases and controls were selected from the on-going Prostate, Lung, Colorectal and Ovarian Cancer Screening Trial and were frequency matched on age, ethnicity, time-period since initial screening, and date of blood draw. Single-locus analyses were conducted using conditional logistic regression. In addition, we did a haplotype analysis for the three IL-10 SNPs tested. Overall, no associations were detected between the seven polymorphisms in the four cytokine genes examined in this study and prostate cancer risk. Further stratifying by use of nonsteroidal anti-inflammatory drugs did not modify the associations. Findings were similar for early or advanced prostate cancers. Similarly, we observed no association between the major IL-10 haplotypes and the risk of prostate cancer. At least seven common polymorphisms in genes of inflammatory cytokines IL-1B, IL-6, IL-8, and IL-10 do not seem to play a role in the risk of prostate cancer.     

Detection of UGT1A10 polymorphisms and their association with orolaryngeal carcinoma risk

BACKGROUND: UGT1A10 exhibits glucuronidating activity against metabolites of the tobacco smoke carcinogen, benzo(a)pyrene, and is expressed highly in numerous target tissues for tobacco-related cancers including the upper aerodigestive tract. The current study was conducted to determine the prevalence of genetic polymorphisms in the UGT1A10-specific region of the UDP-glucuronosyltransferase family 1A locus and their relationship with risk for orolaryngeal carcinoma. METHODS: The authors analyzed UGT1A10-specific sequences in a population of black, white, and Asian individuals. Ten UGT1A10 alleles were identified by direct sequencing of UGT1A10 sequences amplified by polymerase chain reaction (PCR) using DNA purified from buccal cell swabs that were taken from individual subjects. RESULTS: In addition to three silent polymorphisms, three missense polymorphisms were found at codons 139 (Glu > Lys), 240 (Thr > Met), and 244 (Leu > Ile). Using PCR-restriction fragment length polymorphism analysis of buccal cell DNA, the prevalence of the UGT1A10(240Met) variant was less than 0.01% in whites and blacks. Similarly, the prevalence of both the UGT1A10(139Lys) and UGT1A10(244Ile) variants was less than 0.01% in whites but it was significantly higher (0.04 and 0.05, respectively, P < 0.01) in blacks. None of the missense UGT1A10 variants were found in any of the Asian individuals examined. In a case-control study of black individuals, a significant association with orolaryngeal carcinoma risk was found in persons with at least 1 UGT1A10(139Lys) allele (crude odds ratio, 0.29 [95% confidence interval, 0.10-0.81]; adjusted odds ratio, 0.20 [95% confidence interval, 0.05-0.87]). No association was observed for the codon 244 (Leu > Ile) polymorphism. CONCLUSIONS: The data from the current study show that the UGT1A10 gene has several low-frequency missense polymorphisms and that the codon 139 polymorphism is an independent risk factor for orolaryngeal carcinoma in blacks.     

XRCC1 polymorphisms and risk of nasopharyngeal carcinoma: a meta-analysis

Objective: Previous studies on the association between X-ray repair cross-complementing protein 1 (XRCC1) polymorphisms and nasopharyngeal carcinoma (NPC) risk showed inconsistent results. The aim of this study was to evaluate the effects of XRCC1 variants on NPC risk. Methods: A meta-analysis was performed with all eligible studies covering a total of 1,341 cases and 1,425 controls for the Arg194Trp polymorphism, 1,260 cases and 1,207 controls for the Arg280His polymorphism, and 1,644 cases and 1,678 controls for the Arg399Gln polymorphism. Results: No associations was found between Arg194Trp and Arg280His polymorphisms with NPC risk under all contrast models (co-dominant, dominant, and recessive models). However a deleterious effect of the 399Gln genotype was observed under the co-dominant model (Gln/Gln versus Arg/Arg, OR = 1.30, 95% CI : 1.01-1.69, P = 0.04). Under the recessive model (Gln/Gln versus Arg/Arg+Arg/Gln), the P value was marginally significant (OR = 1.28, 95% CI : 1.00-1.65, P = 0.05). However, the effect of the 399Gln genotype on NPC became non-significant after excluding one study from the meta-analysis because of departure from Hardy-Weinberg equilibrium. Conclusions: No associations was found between Arg194Trp and Arg280His polymorphisms with NPC risk, whereas the Arg399Gln genotype was associated with increased risk.     

Inverse association between prostatic polyunsaturated fatty acid and risk of locally advanced prostate carcinoma

BACKGROUND: An effect of fatty acids has been implicated in men with advanced-stage prostate carcinoma and in men who have died of the disease. To evaluate the influence of fatty acids in men with prostate carcinoma at earlier stages, the authors examined the relation between prostatic concentrations of fatty acids and locally advanced prostate carcinoma in men with clinically organ-confined disease. METHODS: Fatty acids were measured by capillary gas chromatography in fresh, nonmalignant prostate tissue specimens collected during surgery from 196 men undergoing radical prostatectomy for localized prostate carcinoma. Two-sided, two-sample Student t tests compared mean concentrations in men with extraprostatic disease (pT3-4N0-1M0) with control men with organ-confined disease. Logistic regression accounted for clinical stage, prostate-specific antigen level, Gleason sum, and other factors. RESULTS: Percent total prostatic polyunsaturated fatty acid (PUFA) was found to be inversely associated with risk of locally advanced prostate carcinoma (n=52) (odds ratio [OR]=0.93, 95% confidence interval [95% CI], 0.87-0.99; P=0.035). Risk of seminal vesicle involvement accounted for this association (OR=0.86, 95% CI, 0.78-0.95; P=0.003). Percent omega-3 fatty acid (eicosapentanoic + docosahexanoic acids) and percent arachidonic acid also were found to be inversely related to the risk of seminal vesicle involvement (OR=0.52, 95% CI, 0.30-0.90; P=0.02; and OR=0.84, 95% CI,; 0.75-0.95; P=0.005, respectively). CONCLUSIONS: Prostatic PUFA levels appear to influence the risk of locally advanced prostate carcinoma in men with clinically organ-confined disease. This association may be mediated through the immune system.     

HBV感染与肝癌组织CDKN2A基因甲基化关系的研究

目的:探讨HBV感染和CDKN2A异常甲基化之间的潜在关联及其相互作用在肝癌形成过程中的作用。方法:对44例肝癌患者癌组织及癌旁组织CDKN2A甲基化状况、血清HBV感染标志物等到进行了检测分析。血清HBV、HCV感染标志物采用全自动化学发光分析仪进行检测。采用酚、氯仿法抽提组织DNA,用CDKN2A甲基化特异性引物进行PCR扩增,并检测特异性产物。患者按HBV感染情况进行分组,统计分析。结果:CDKN2A甲基化产物在肝癌组织中的总检出率为70.5%(31/44)。其中,HBV相关肝癌组和非病毒相关肝癌组CDKN2A甲基化率为90.6%(29/32)和16.7%(2/12),P=0.000。对HBV相关肝癌进一步分组分析,HBsAg /HBeAg 、HBsAg /HBeAg-及HBcAb /HBcAb-三组,三组之间差异无统计学意义(P=0.568)。经非参数相关和logistic回归分析,发现:CDKN2A甲基化与性别、肿瘤分化程度无明显相关(R2=0.11,P=0.650),而与HBV感染,特别是HBsAg密切相关(R2=0.37,P=0.02)。结论:在肝癌形成过程中,HBV可能通过促进抑癌基因,如CDKN2A等的异常甲基化,使CDKN2A失活,肝细胞正常的生长调控机制失常,形成肝癌,这也可能是HBV导致肝癌形成的机制之一。     

GSTM1, GSTT1, and GSTP1 polymorphisms and risk of advanced colorectal adenoma.

Cigarette smoking is a risk factor for colon adenoma. The glutathione S-transferase enzymes are involved in the detoxification of carcinogenic compounds including those found in tobacco smoke, and thus, may be important modifiers of individual risk of developing this disease. We examined the prevalence of GSTM1 and GSTT1 gene deletions, and two GSTP1 polymorphisms in 772 cases with advanced colorectal adenomas (>1 cm, villous elements or high-grade dysplasia) of the distal colon (descending or sigmoid colon or rectum) and 777 sigmoidoscopy negative controls enrolled in the screening arm of the Prostate, Lung, Colorectal, and Ovarian Cancer Screening Trial. Epidemiologic data on smoking was collected by self-administered questionnaire and DNA was extracted from whole blood or buffy coat. For GSTM1 and GSTT1, we used a newly developed TaqMan-based assay capable of discriminating heterozygous (+/-) individuals from those with two active alleles (+/+) and homozygous deletions (-/-). For GSTP1, the I105V and the A114V substitutions were identified using end point 5' nuclease assays (TaqMan). Adjusted odds ratios (OR) and 95% confidence intervals (95% CI) were determined using unconditional logistic regression, controlling for age, race, and gender. Advanced adenoma risk was increased in current/former smokers (OR, 1.4; 95% CI, 1.2-1.8). Risks were decreased in subjects with > or =1 inactive GSTM1 alleles (OR, 0.6; 95% CI, 0.4-0.9); and the association was independent of smoking status (P interaction = 0.59). Having > or =1 inactive GSTT1 allele was associated with increased risk among smokers (OR, 1.4; 95% CI, 1.1-1.9; P trend = 0.02) but not among never smokers (OR, 0.9; 95% CI, 0.6-1.3) and a significant interaction between smoking and genotype was observed (P interaction = 0.05). In summary, this is the first study to report associations between colorectal adenomas and GSTM1 wild-type and GSTT1 null allele among smokers. These findings only became apparent using a newly developed assay able to distinguish heterozygous from wild-type individuals. Our data provide evidence that phenotypic differences between these two groups exist.     

DNA repair gene XRCC1 and XPD polymorphisms and risk of prostate cancer.

The X-ray repair cross-complementing group 1 (XRCC1) and xeroderma pigmentosum group D (XPD) genes are involved in base excision repair and nucleotide excision repair of DNA repair pathways, respectively. A growing body of evidence suggests that XRCC1 and XPD are important in environmentally induced cancers, and polymorphisms in both genes have been identified. To determine whether the XRCC1 (codon Arg399Gln) and XPD (codon Asp312Asn and codon Lys751Gln) polymorphisms are associated with prostate cancer susceptibility, we genotyped these polymorphisms in a primarily Caucasian sample of 506 sibships (n = 1,117) ascertained through a brother with prostate cancer. Sibships were analyzed with a Cox proportional hazards model with age at prostate cancer diagnosis as the outcome. Of the three polymorphisms investigated, only the XPD codon 312 Asn/Asn genotype had an odds ratio (OR) significantly different from one (OR, 1.61; 95% CI, 1.03-2.53). Analyses stratified by the clinical characteristics of affected brothers in the sibship did not reveal any significant heterogeneity in risk. In exploring two-way gene interactions, we found a markedly elevated risk for the combination of the XPD codon 312 Asn/Asn and XRCC1 codon 399 Gln/Gln genotypes (OR, 4.81; 95% CI, 1.66-13.97). In summary, our results suggest that the XPD codon 312 Asn allele may exert a modest positive effect on prostate cancer risk when two copies of the allele are present, and this effect is enhanced by the XRCC codon 399 Gln allele in its recessive state.