Anand P. Chokkalingam

Prostate cancer epidemiology.

Prostate cancer is the most common non-skin cancer among men in most western populations, and it is the second leading cause of cancer death among U.S. men. Despite its high morbidity, the etiology of prostate cancer remains largely unknown. Advancing age, race, and a family history of prostate cancer are the only established risk factors. Many putative risk factors, including androgens, diet, physical activity, sexual factors, inflammation, and obesity, have been implicated, but their roles in prostate cancer etiology remain unclear. It is estimated that as much as 42% of the risk of prostate cancer may be accounted for by genetic influences, including individual and combined effects of rare, highly penetrant genes, more common weakly penetrant genes, and genes acting in concert with each other. Numerous genetic variants in the androgen biosynthesis/metabolism, carcinogen metabolism, DNA repair, and chronic inflammation pathways, have been explored, but the results are largely inconclusive. The pathogenesis of prostate cancer likely involves interplay between environmental and genetic factors. To unravel these complex relationships, large well-designed interdisciplinary epidemiologic studies are needed. With newly available molecular tools, a new generation of large-scale multidisciplinary population-based studies is beginning to investigate gene-gene and gene-environment interactions. Results of these studies may lead to better detection, treatment, and, ultimately, prevention of prostate cancer.

Genetic Variants of DNA Repair Genes and Prostate Cancer: A Population-Based Study

As part of a population-based case-control study in Shanghai, China, we investigated whether variants in several DNA repair genes, either alone or in conjunction with other risk factors, are associated with prostate cancer risk. Genomic DNA from 162 patients newly diagnosed with prostate cancer and 251 healthy men randomly selected from the population were typed for five nonsynonymous DNA repair markers. We found that the XRCC1-Arg399Gln AA and the MGMT-Leu84Phe CT+TT genotypes were associated with an increased risk of prostate cancer [odds ratio (OR), 2.18; 95% confidence interval (CI), 0.99-4.81 and OR, 1.99; 95% CI, 1.19-3.34, respectively]. In contrast, XRCC3-Thr241Met, XPD-Lys751Gln, and MGMT-Ile143Val markers showed no significant associations with risk, although due to the much lower frequency of their variant alleles in this population we cannot rule out small to modest effects. There was a significant interaction between the MGMT-84 marker and insulin resistance (Pinteraction = 0.046). Relative to men with the MGMT-84 CC genotype and a low insulin resistance (<0.097), those having the CT-TT genotype and a greater insulin resistance had a 5.4-fold risk (OR, 5.39; 95% CI, 2.46-11.82). In addition, for the XRCC3-241 marker, relative to men with the CC genotype and a low intake of preserved foods (<12.7 g/d), those harboring the CT+TT genotype and having a higher intake of preserved foods (>12.7 g/d), which contain nitrosamines and nitrosamine precursors, had a significantly increased risk of prostate cancer risk (OR, 2.62; 95% CI, 1.13-6.06). In contrast, men with the CT+TT genotype and a low intake of preserved foods had a 69% reduction in risk (OR, 0.31; 95% CI, 0.10-0.96; Pinteraction = 0.005). These results suggest that genetic variants in the DNA repair pathways may be involved in prostate cancer etiology and that other risk factors, including preserved foods and insulin resistance, may modulate prostate cancer risk in combination with genetic susceptibility in these repair pathways. Replication in larger studies is necessary to preclude chance findings, particularly those among subgroups, and clarify the mechanisms involved.

Occupation and prostate cancer risk in Sweden.

To provide new leads regarding occupational prostate cancer risk factors, we linked 36,269 prostate cancer cases reported to the Swedish National Cancer Registry during 1961 to 1979 with employment information from the 1960 National Census. Standardized incidence ratios for prostate cancer, within major (1-digit), general (2-digit), and specific (3-digit) industries and occupations, were calculated. Significant excess risks were seen for agriculture-related industries, soap and perfume manufacture, and leather processing industries. Significantly elevated standardized incidence ratios were also seen for the following occupations: farmers, leather workers, and white-collar occupations. Our results suggest that farmers; certain occupations and industries with exposures to cadmium, herbicides, and fertilizers; and men with low occupational physical activity levels have elevated prostate cancer risks. Further research is needed to confirm these findings and identify specific exposures related to excess risk in these occupations and industries.

MDR1 gene variants, indoor insecticide exposure, and the risk of childhood acute lymphoblastic leukemia

Objective: The multidrug resistance (MDR) 1 gene encodes a membrane transporter called P-glycoprotein, which plays an important role in protecting cells against lipophilic xenobiotics by way of an ATP-dependent cellular efflux mechanism. Among children enrolled in the Northern California Childhood Leukemia Study, we examined the susceptibility conferred by MDR1 single nucleotide polymorphisms (SNP) and predicted haplotypes and whether they modify the association between indoor insecticide exposure and risk of childhood acute lymphoblastic leukemia (ALL). Methods: Buccal cell DNA from ALL cases (n = 294) and controls (n = 369) individually matched on gender, date of birth, Hispanic status, and maternal race were whole genome amplified and genotyped for four MDR1 SNPs, T−129C (rs3213619), C1236T (rs1128503), G2677T/A (rs2032582), and C3435T (rs1045642). Detailed and time-specific information on household pesticide use was obtained using in-home interviews with the mother. Results: Allele frequencies in non-Hispanic White and Hispanic controls were similar, and with the exception of T−129C, seemed to be in strong linkage disequilibrium. Overall, the SNPs considered individually or within haplotypes (C1236T-G2677T/A-C3435T) were not significantly associated with childhood ALL. However, we observed strong evidence of a differential effect of indoor insecticide exposure (interaction odds ratio, 0.31; 95% confidence interval, 0.15-0.64; P = 0.025) on risk of ALL between carriers and noncarriers of haplotype CGC. Conclusion: These preliminary data suggest that children carrying the haplotype CGC may be less susceptible to the leukemogenic effects of indoor insecticide exposures. Future studies are needed to confirm these findings. (Cancer Epidemiol Biomarkers Prev 2007;16(6):1172–7)

A global DNA methylation and gene expression analysis of early human B-cell development reveals a demethylation signature and transcription factor network

The epigenetic changes during B-cell development relevant to both normal function and hematologic malignancy are incompletely understood. We examined DNA methylation and RNA expression status during early B-cell development by sorting multiple replicates of four separate stages of pre-B cells derived from normal human fetal bone marrow and applied high-dimension DNA methylation scanning and expression arrays. Features of promoter and gene body DNA methylation were strongly correlated with RNA expression in multipotent progenitors (MPPs) both in a static state and throughout differentiation. As MPPs commit to pre-B cells, a predominantly demethylating phenotype ensues, with 79% of the 2966 differentially methylated regions observed involving demethylation. Demethylation events were more often gene body associated rather than promoter associated; predominantly located outside of CpG islands; and closely associated with EBF1, E2F, PAX5 and other functional transcription factor (TF) sites related to B-cell development. Such demethylation events were accompanied by TF occupancy. After commitment, DNA methylation changes appeared to play a smaller role in B-cell development. We identified a distinct development-dependent demethylation signature which has gene expression regulatory properties for pre-B cells, and provide a catalog reference for the epigenetic changes that occur in pre-B-cell leukemia and other B-cell-related diseases.

NQO1 Polymorphisms and De Novo Childhood Leukemia: A HuGE Review and Meta-Analysis

Polymorphisms in NQO1, a gene coding for the phase II enzyme involved in the detoxification of quinone carcinogens, have been associated with childhood leukemia in some studies, although the observed direction and magnitude of effects have been inconsistent. Therefore, the authors systematically reviewed all published reports describing the effect of NQO1 in de novo childhood leukemia and conducted a meta-analysis of 7 case-control studies that examined the association between NQO1*2 and childhood leukemia. Although a family-based study previously demonstrated over-transmission of this allele among childhood acute lymphoblastic leukemia cases, the meta-analysis showed that the presence of a NQO1*2 variant allele, which reduces the activity of the enzyme NAD(P)H:quinone oxidoreductase 1 (NQO1), had no significant effect on childhood leukemia. However, there was an increased risk associated with having at least 1 copy of the NQO1*2 allele in a subset of cases with MLL translocations (summary odds ratio = 1.39, 95% confidence interval: 0.98, 1.97). Heterogeneity between studies may be due to differences in population exposures to NQO1 substrates and small sample sizes, as well as potential population stratification in non-family-based studies. Therefore, further research is warranted on the role of NQO1 polymorphisms in the etiology of childhood leukemia, especially among MLL-positive leukemias.

Two susceptibility loci identified for prostate cancer aggressiveness

Most men diagnosed with prostate cancer will experience indolent disease; hence discovering genetic variants that distinguish aggressive from non-aggressive prostate cancer is of critical clinical importance for disease prevention and treatment. In a multistage, case-only genome-wide association study of 12,518 prostate cancer cases, we identify two loci associated with Gleason score, a pathological measure of disease aggressiveness: rs35148638 at 5q14.3 (RASA1, P=6.49×10-9) and rs78943174 at 3q26.31 (NAALADL2, P=4.18×10-8). In a stratified case-control analysis, the SNP at 5q14.3 appears specific for aggressive prostate cancer (P=8.85×10-5) with no association for non-aggressive prostate cancer compared to controls (P=0.57). The proximity of these loci to genes involved in vascular disease suggests potential biological mechanisms worthy of further investigation.

Early life exposure to infections and risk of childhood acute lymphoblastic leukemia.

Evidence from a growing number of studies indicates that exposure to common infections early in life may be protective against childhood acute lymphoblastic leukemia (ALL). We examined the relationship between three measures of early life exposure to infections—daycare attendance, birth order and common childhood infections in infancy—with the risk of ALL in non‐Hispanic white and Hispanic children, two ethnicities that show sociodemographic differences. The analysis included 669 ALL cases (284 non‐Hispanic whites and 385 Hispanics) and 977 controls (458 non‐Hispanic whites and 519 Hispanics) ages 1–14 years enrolled in the Northern California Childhood Leukemia Study (NCCLS). When the three measures were evaluated separately, daycare attendance by the age of 6 months (odds ratio [OR] for each thousand child‐hours of exposure = 0.90, 95% confidence interval [CI]: 0.82–1.00) and birth order (OR for having an older sibling = 0.68, 95% CI: 0.50–0.92) were associated with a reduced risk of ALL among non‐Hispanic white children but not Hispanic children, whereas ear infection before age 6 months was protective in both ethnic groups. When the three measures were assessed simultaneously, the influence of daycare attendance (OR = 0.83, 95% CI: 0.73–0.94) and having an older sibling (OR = 0.59, 95% CI: 0.43–0.83) became stronger for non‐Hispanic white children. In Hispanic children, a strong reduction in risk associated with ear infections persisted (OR = 0.45, 95% CI: 0.25–0.79). Evidence of a protective role for infection‐related exposures early in life is supported by findings in both the non‐Hispanic white and Hispanic populations within the NCCLS.

Profound Deficit of IL10 at Birth in Children Who Develop Childhood Acute Lymphoblastic Leukemia

Background: Childhood acute lymphoblastic leukemia (ALL) may originate via abnormal immune responses to infectious agents. It is unknown whether prenatal immune development may differ in children who develop the disease. The current study examines the association between neonatal cytokine profiles, a proxy measure for a childs prenatal immune development, and childhood ALL. Methods: Neonatal blood spots of 116 childhood ALL cases and 116 controls living in California were ascertained. Eleven cytokines associated with Th1, Th2, and Th17 lymphocytes were measured using a multiplex bead–based assay. Unconditional logistic regression was done to estimate the odds ratio (OR) by measuring the association between neonatal cytokines and ALL adjusted for age, sex, race/ethnicity, and household income. Results: Of the 11 cytokines measured, 5 [interleukin (IL)4, IL6, IL10, IL12, and IL13] were detectable. Except for IL12, the other 4 cytokines were all significantly lower among cases than controls. In a multivariable model including the 5 cytokines, only IL10 remained independently associated with childhood ALL with an OR = 0.04, 95% CI: 0.01 to 0.18, comparing the highest tertile to the lowest tertile. Conclusions: A childs neonatal level of IL10, a key regulator for modulating the intensity and duration of immune responses, is associated with his/her subsequent risk of developing ALL. Impact: The current analysis shows that children with ALL may have a dysregulated immune function present at birth. Cancer Epidemiol Biomarkers Prev; 20(8); 1736–40. ©2011 AACR.

Novel childhood ALL susceptibility locus BMI1-PIP4K2A is specifically associated with the hyperdiploid subtype.

To the editor: A recent genome-wide association study of childhood acute lymphoblastic leukemia (ALL) by Xu et al[1][1] has identified a novel susceptibility locus encompassing BMI1 - PIP4K2A at chr10p12.31-12.2, bringing the number of known ALL risk loci to 5 (including ARID5B , IKZF1 , CEBPE, and