Yuyan Liao

Short Telomere Length and Breast Cancer Risk: A Study in Sister Sets

Telomeres consist of a tandem repeats of the sequence TTAGGG at the ends of chromosomes and play a key role in the maintenance of chromosomal stability. Previous studies indicated that short telomeres are associated with increased risk for human bladder, head and neck, lung, and renal cell cancer. We investigated the association between white blood cell telomere length and breast cancer risk among 268 family sets (287 breast cancer cases and 350 sister controls). Telomere length was assessed by quantitative PCR. The mean telomere length was shorter in cases (mean, 0.70; range, 0.03-1.95) than in unaffected control sisters (mean, 0.74; range, 0.03-2.29), but no significant difference was observed (P = 0.11). When subjects were categorized according to the median telomere length in controls (0.70), affected sisters had shorter telomeres compared with unaffected sisters after adjusting for age at blood donation and smoking status [odds ratio (OR), 1.3; 95% confidence interval (95% CI), 0.9-1.8], but the association was not statistically significant. The association by quartile of telomere length (Q4 shortest versus Q1 longest) also supported an increase in risk from shorter telomere length, although the association was not statistically significant (OR, 1.6; 95% CI, 0.9-2.7). This association was more pronounced among premenopausal women (OR, 2.1; 95% CI, 0.8-5.5) than postmenopausal women (OR, 1.3; 95% CI, 0.5-3.6 for Q4 versus Q1). If these associations are replicated in larger studies, they provide modest epidemiologic evidence that shortened telomere length may be associated with breast cancer risk.

Global methylation profiles in DNA from different blood cell types

DNA methylation measured in white blood cell DNA is increasingly being used as in studies of cancer susceptibility. However, little is known about the correlation between different assays to measure global methylation and whether the source of DNA matters when examining methylation profiles in different blood cell types. Using information from 620 women, 217 and 403 women with DNA available from granulocytes (Gran), and total white blood cells (WBC), respectively, and 48 women with DNA available from four different sources (WBC, Gran, mononuclear (MN), and lymphoblastoid cell lines (LCL)), we compared DNA methylation for three repetitive elements (LINE1, Sat2, Alu) by MethyLight, luminometric methylation assay (LUMA), and [3H]-methyl acceptance assay. For four of the five assays, DNA methylation levels measured in Gran were not correlated with methylation in LBC, MN, or WBC; the exception was Sat2. DNA methylation in LCL was correlated with methylation in MN and WBC for the [3H]-methyl acceptance, LINE1, and Alu assays. Methylation in MN was correlated with methylation in WBC for the [3H]-methyl acceptance and LUMA assays. When we compared the five assays to each other by source of DNA, we observed statistically significant positive correlations ranging from 0.3-0.7 for each cell type with one exception (Sat2 and Alu in MN). . Among the 620 women stratified by DNA source, correlations among assays were highest for the three repetitive elements (range 0.39-0.64). Results from the LUMA assay were modestly correlated with LINE1 (0.18-0.20). These results suggest that both assay and source of DNA are critical components in the interpretation of global DNA methylation patterns from WBC.

Prenatal Smoke Exposure and Genomic DNA Methylation in a Multiethnic Birth Cohort

Background: Exposure to prenatal tobacco smoke (PTS) has been associated with a number of health outcomes in the offspring, including some childhood cancers. Lower levels of genomic DNA methylation have also been associated with several types of cancers. We investigated whether PTS was associated with global DNA methylation levels in the offspring. Methods: Our sample was drawn from a birth cohort of women born between 1959 and 1963 in New York City (n = 90). We measured methylation of repetitive elements (Sat2, Alu, LINE-1) from peripheral blood granulocytes. We combined prospectively collected data on PTS with adult epidemiologic data and blood samples collected in 2001 to 2007 (mean age, 43 years). We used linear regression to assess the association between PTS and repetitive element methylation. Results: Thirty-six percent of mothers smoked during pregnancy. We observed an inverse association between PTS and Sat2 methylation. This inverse association remained even after adjustment for potential mediators including child environmental tobacco smoke exposure, birth size, postnatal weight and height changes, and adult smoking status and alcohol intake (β = −0.22, 95% confidence interval = −0.40 to −0.03 for ever exposed to PTS vs. never exposed using models of log-transformed methylation levels). PTS exposure was not statistically significantly associated with LINE-1 or Alu methylation. Conclusions: PTS exposure, measured at the time of pregnancy and not retrospectively reported, was associated with a decrease in Sat2 methylation but not LINE-1 or Alu methylation. Impact: If replicated in larger studies, this study supports a persistent effect of PTS on DNA methylation levels, as measured by Sat2, in adulthood. Cancer Epidemiol Biomarkers Prev; 20(12); 2518–23. ©2011 AACR.

Medical Advances and Racial/ethnic Disparities in Cancer Survival

Background: Although advances in early detection and treatment of cancer improve overall population survival, these advances may not benefit all population groups equally and may heighten racial/ethnic differences in survival. Methods: We identified cancer cases in the Surveillance, Epidemiology and End Results program, who were ages ≥20 years and diagnosed with one invasive cancer in 1995 to 1999 (n = 580,225). We used 5-year relative survival rates to measure the degree to which mortality from each cancer is amenable to medical interventions (amenability index). We used Kaplan-Meier methods and Cox proportional hazards regression to estimate survival differences between each racial/ethnic minority group relative to Whites, by the overall amenability index, and three levels of amenability (nonamenable, partly amenable, and mostly amenable cancers, corresponding to cancers with 5-year relative survival rate <40%, 40-69%, and ≥70%, respectively), adjusting for gender, age, disease stage, and county-level poverty concentration. Results: As amenability increased, racial/ethnic differences in cancer survival increased for African Americans, American Indians/Native Alaskans, and Hispanics relative to Whites. For example, the hazard ratios (95% confidence intervals) for African Americans versus Whites from nonamenable, partly amenable, and mostly amenable cancers were 1.05 (1.03-1.07), 1.38 (1.34-1.41), and 1.41 (1.37-1.46), respectively. Asians/Pacific Islanders had similar or longer survival relative to Whites across amenability levels; however, several subgroups experienced increasingly poorer survival with increasing amenability. Conclusions: Cancer survival disparities for most racial/ethnic minority populations widen as cancers become more amenable to medical interventions. Efforts in developing cancer control measures must be coupled with specific strategies for reducing the expected disparities. (Cancer Epidemiol Biomarkers Prev 2009;18(10):2701–8)

Repetitive element DNA methylation levels in white blood cell DNA from sisters discordant for breast cancer from the New York site of the Breast Cancer Family Registry

Global decreases in DNA methylation, particularly in repetitive elements, have been associated with genomic instability and human cancer. Emerging, though limited, data suggest that in white blood cell (WBC) DNA levels of methylation, overall or in repetitive elements, may be associated with cancer risk. We measured methylation levels of three repetitive elements [Satellite 2 (Sat2)], long interspersed nuclear element-1 (LINE-1) and Alu) by MethyLight, and LINE-1 by pyrosequencing in a total of 282 breast cancer cases and 347 unaffected sisters from the New York site of the Breast Cancer Family Registry (BCFR) using DNA from both granulocytes and total WBC. We found that methylation levels in all markers were correlated between sisters (Spearman correlation coefficients ranged from 0.17 to 0.55). Sat2 methylation was statistically significantly associated with increased breast cancer risk [odds ratio (OR) = 2.09, 95% confidence interval (CI) = 1.09-4.03; for each unit decrease in the natural log of the methylation level, OR = 2.12, 95% CI = 0.88-5.11 for the lowest quartile compared with the highest quartile]. These associations were only observed in total WBC but not granulocyte DNA. There was no association between breast cancer and LINE-1 and Alu methylation. If replicated in larger prospective studies, these findings support that selected markers of epigenetic changes measured in WBC, such as Sat2, may be potential biomarkers of breast cancer risk.

Adult global DNA methylation in relation to pre-natal nutrition

BACKGROUND Exposure to a pre-natal famine environment has been associated with a persistent decrease in DNA methylation of the IGF2 gene, although study findings on other loci have been highly variable. There have been no studies to date of the relation between pre-natal famine and overall global DNA methylation in adulthood. METHODS Our study population includes 350 births with pre-natal exposure to the Dutch famine of 1944-45 selected from three birth clinics, 290 births from these clinics born before or after the famine as unexposed time controls and 307 same-sex siblings of either birth group as unexposed family controls. All study subjects were interviewed and underwent a medical examination at a mean age of 58 years when blood samples were also collected. As measures of genomic DNA methylation, we analysed two repetitive elements, LINE-1 (long interspersed nucleotide element 1) and Sat2 (Satellite 2 DNA sequence) by pyrosequencing and MethyLight, respectively, and overall genomic DNA methylation using the Luminometric methylation assay (LUMA). RESULTS Mean DNA methylation by LUMA was 75.2% [standard deviation (SD) 4.7], by LINE-1 was 77.1% (SD 2.5) and by Sat2 was 122.2 (SD 56.2). Pre-natal famine exposure was associated with negligible changes in all three assays {LUMA: -0.16% [95% confidence interval (95% CI) -0.49 to 0.81], P = 0.63; LINE-1: -0.05 % (95% CI -0.33 to 0.22), P = 0.70; and Sat2: -0.51% (95% CI -7.38 to 6.36), P = 0.88} relative to unexposed controls, adjusting for age at examination and within family clustering. CONCLUSION Our results show no relation between overall global DNA methylation in adults and pre-natal famine exposure. Further work should focus on selected regions in the genome that may be differentially methylated in response to changes in early life exposures and predict adult health outcomes.

Plasma Protein Carbonyls and Breast Cancer Risk in Sisters Discordant for Breast Cancer from the New York Site of the Breast Cancer Family Registry

Reactive oxygen species are important in the pathogenesis of many diseases, including breast cancer. Several population-based case-control studies have shown that various biomarkers of oxidative stress are associated with an increase in breast cancer risk. We selected sisters discordant for breast cancer (n=645) from the New York site of the Breast Cancer Family Registry to explore factors that contribute to variation in plasma protein carbonyls, and to determine whether this biomarker is associated with an increase in breast cancer risk among those with a family history. Late age at menarche, hormone replacement therapy use, and Hispanic race were significantly associated with lower plasma protein carbonyl levels in unaffected sisters. Plasma protein carbonyls were associated with an increase in breast cancer risk [Q2 odds ratio (OR), 1.4; 95% confidence interval (CI), 0.8-2.7; Q3 OR, 2.4; 95% CI, 1.1-4.9; Q4 OR, 1.9; 95% CI, 0.8-4.2], although not in a dose-dependent manner. These data suggest that oxidative damage is a risk factor for breast cancer in high-risk women.

Global DNA methylation levels in white blood cell DNA from sisters discordant for breast cancer from the New York site of the Breast Cancer Family Registry

Lower global DNA methylation is associated with genomic instability and it is one of the epigenetic mechanisms relevant to carcinogenesis. Emerging evidence for several cancers suggests that lower overall levels of global DNA methylation in blood are associated with different cancer types, although less is known about breast cancer. We examined global DNA methylation levels using a sibling design in 273 sisters affected with breast cancer and 335 unaffected sisters from the New York site of the Breast Cancer Family Registry. We measured global DNA methylation in total white blood cell (WBC) and granulocyte DNA by two different methods, the [3H]-methyl acceptance assay and the luminometric methylation assay (LUMA). Global methylation levels were only modestly correlated between sisters discordant for breast cancer (Spearman correlation coefficients ranged from -0.08 to 0.24 depending on assay and DNA source). Using conditional logistic regression models, women in the quartile with the lowest DNA methylation levels (as measured by the [3H]-methyl acceptance assay) had a 1.8-fold (95% CI = 1.0–3.3) higher relative association with breast cancer than women in the quartile with the highest DNA methylation levels. When we examined the association on a continuous scale, we also observed a positive association (odds ratio, OR = 1.3, 95% CI = 1.0–1.7, for a one unit change in the natural logarithm of the DPM/μg of DNA). We observed no association between measures by the LUMA assay and breast cancer risk. If replicated in prospective studies, this study suggests that global DNA methylation levels measured in WBC may be a potential biomarker of breast cancer risk even within families at higher risk of cancer.

XRCC1 polymorphisms and breast cancer risk from the New York Site of the Breast Cancer Family Registry: A family-based case-control study

Background: XRCC1 is a scaffold protein involved in the early and late stages of Base Excision Repair (BER). Three DNA polymorphisms occur in XRCC1, resulting in non-synonymous amino acid changes, which could alter the binding or regulatory activities of XRCC1. Materials and Methods: We used a family-based case-control study design to evaluate the association between XRCC1 polymorphisms and breast cancer risk. Participants were breast cancer cases and their unaffected sisters enrolled in the New York Site of the Breast Cancer Family Registry. Conditional logistic regression was used to assess associations between genotype and breast cancer. XRCC1 mRNA levels and DNA nicking activity were measured in lymphoblastoid cell lines from unaffected sisters to determine whether the XRCC1 R399Q polymorphism has a functional effect on expression or protein activity. Results: XRCC1 194W was associated with a non-significant increase in breast cancer, while XRCC1 280H and XRCC1 399Q were associated with a non-significant decrease in breast cancer. We found a significant increase in XRCC1 expression in 399Q/Q lymphoblastoid cell lines from unaffected sisters (n=28, P=0.03). An increase in median nicking activity was not statistically significant. Conclusions: Our results suggest that XRCC1 399Q may alter mRNA expression and DNA repair phenotype, although the main effects of the genotype were not significantly associated with familial cancer risk. Additional research on the regulation of XRCC1 expression will contribute to an understanding of how this polymorphism may impact disease risk.

Reproductive risk factors and oestrogen/progesterone receptor-negative breast cancer in the Breast Cancer Family Registry

Background:Oestrogen receptor (ER)- and progesterone receptor (PR)-negative (ER−PR−) breast cancer is associated with poorer prognosis compared with other breast cancer subtypes. High parity has been associated with an increased risk of ER−PR− cancer, but emerging evidence suggests that breastfeeding may reduce this risk. Whether this potential breastfeeding benefit extends to women at high risk of breast cancer remains critical to understand for prevention.Methods:Using population-based ascertained cases (n=4011) and controls (2997) from the Breast Cancer Family Registry, we examined reproductive risk factors in relation to ER and PR status.Results:High parity (⩾3 live births) without breastfeeding was positively associated only with ER−PR− tumours (odds ratio (OR)=1.57, 95% confidence interval (CI), 1.10–2.24); there was no association with parity in women who breastfed (OR=0.93, 95% CI 0.71–1.22). Across all race/ethnicities, associations for ER−PR− cancer were higher among women who did not breastfeed than among women who did. Oral contraceptive (OC) use before 1975 was associated with an increased risk of ER−PR− cancer only (OR=1.32, 95% CI 1.04–1.67). For women who began OC use in 1975 or later there was no increased risk.Conclusions:Our findings support that there are modifiable factors for ER−PR− breast cancer and that breastfeeding in particular may mitigate the increased risk of ER−PR− cancers seen from multiparity.