Is the association between cigarette smoking and breast cancer modified by genotype? A review of epidemiologic studies and meta-analysis

Xeroderma pigmentosum complementation group C genotypes/diplotypes play no independent or interaction role with polycyclic aromatic hydrocarbons-DNA adducts for breast cancer risk

Xeroderma pigmentosum complementation group C (XPC) is an important DNA nuclear excision repair (NER) gene that recognises the damage caused by a variety of bulky DNA adducts. We evaluated the association of two common non-synonymous polymorphisms in XPC (Ala499Val and Lys939Gln) with breast cancer risk in the Long Island Breast Cancer Study Project (LIBCSP), a population-based case-control study. Genotyping of 1067 cases and 1110 controls was performed by a high throughput assay with fluorescence polarisation. There were no overall associations between XPC polymorphisms and breast cancer risk. A diplotype CC-CC was significantly associated with increased breast cancer risk compared with diplotype CA-CA (OR=1.4, 95%CI: 1.0-1.9), but was not significant when compared with all other diplotypes combined (OR=1.22, 95%CI: 0.97-1.53). No modification effects were observed for XPC genotypes by cigarette smoking status, smoking pack-years or polycyclic aromatic hydrocarbons (PAH)-DNA adducts. The increase in breast cancer risk was slightly more pronounced among women with detectable PAH-DNA adducts and carrying the diplotype CC-CC (OR=1.6, 95%CI: 1.1-2.2) compared to women with non-detectable PAH-DNA adducts carrying other diplotypes combined, but no statistically significant interaction was observed (P(interaction)=0.69). These data suggest that XPCs have neither independent effects nor interactions with cigarette smoking and PAH-DNA adducts for breast cancer risk. Further studies with multiple genetic polymorphisms in NER pathway are warranted.

A meta-analysis of the association of N-acetyltransferase 2 gene (NAT2) variants with breast cancer

The N-acetyltransferase 2 gene (NAT2) product is an enzyme important in carcinogen metabolism via activation and detoxification pathways. Therefore, NAT2 variants may represent underlying susceptibility to breast cancer. Because a number of studies of the association of NAT2 with breast cancer have been published, the authors performed a meta-analysis. They extracted all relevant data to examine evidence for a main effect (i.e., the effect in a model that does not include any interactions) of NAT2 phenotype and genotype on breast cancer risk. They summarized the evidence for modification by smoking and meat intake, sources of exposure to aromatic and heterocyclic amines, respectively, which are metabolized by NAT2. The authors identified seven studies that measured NAT2 phenotype and 20 studies that deduced phenotype via genotyping. They found no evidence for heterogeneity (Cochran's Q statistic p=0.74) and no statistically significant increased risk from NAT2 acetylation (slow/rapid) for breast cancer (summary odds ratio=1.02, 95% confidence interval: 0.95, 1.08). These results suggest that there is no overall association between the NAT2 slow- or rapid-acetylation phenotype and breast cancer risk. However, some evidence suggests that smoking may modify this association.

Glutathione S-transferase M1 and P1 polymorphisms and risk of breast cancer and fibrocystic breast conditions in Chinese women

Enzymes encoded by the glutathione S-tranferase mu 1 (GSTM1) and pi 1 (GSTP1) genes, which are expressed in breast tissue, catalyze the detoxification of endogenous and exogenous electrophiles. Reduced enzyme activity, due to carriage of the GSTM1 deletion or the GSTP1 Ile105Val Val allele, may therefore affect susceptibility to breast cancer and related conditions. In a case-control study of Chinese women, we examined whether these polymorphisms were associated with risk of breast cancer and fibrocystic breast conditions. Women diagnosed with breast cancer (n=615) or fibrocystic breast conditions (n=467) were compared to women without clinical breast disease (n=878). We also examined whether these associations differed by menopausal status or by presence of proliferation in the extra-tumoral epithelium among women with breast cancer and in lesions among women with fibrocystic conditions. No overall association of either GST polymorphism with risk of breast cancer or fibrocystic breast conditions was observed. There was some evidence of slightly elevated cancer risk associated with carriage of the GSTM1 null genotype and at least one GSTP1 105-Val allele (OR=1.33, 95% CI, 0.99-1.80), compared to carriage of the GSTM1 non-null and GSTP1 Ile/Ile genotypes. This relationship was stronger in women who had breast cancer with extra-tumoral tissue proliferation (OR=1.77, 95% CI, 1.03-3.04). Our results suggest that GSTM1 and GSTP1 genotypes do not individually influence susceptibility to breast cancer or fibrocystic breast conditions. The observed increased risk of breast cancer associated with joint carriage of the GSTM1 null genotype and GSTP1 105-Val allele needs confirmation in other studies.

Genetic susceptibility according to three metabolic pathways in cancers of the lung and bladder and in myeloid leukemias in nonsmokers

BACKGROUND

We chose a set of candidate single nucleotide polymorphisms (SNPs) to investigate gene-environment interactions in three types of cancer that have been related to air pollution (lung, bladder and myeloid leukemia).

PATIENTS AND METHODS

The study has been conducted as a nested case-control study within the European Prospective Investigation into Cancer and Nutrition cohort (409 cancer cases and 757 matched controls). We included never and ex-smokers. SNPs were in genes involved in oxidative stress, phase I metabolizing genes, phase II metabolizing genes and methylenetetrahydrofolate reductase (MTHFR).

RESULTS

The most notable findings are: GSTM1 deletion and bladder cancer risk [odds ratio (OR) = 1.60; 95% confidence interval 1.00-2.56]; CYP1A1 and leukemia (2.22, 1.33-3.70; heterozygotes); CYP1B1 and leukemia (0.47, 0.27-0.84; homozygotes); MnSOD and leukemia (1.91, 1.08-3.38; homozygotes) and NQO1 and lung cancer (8.03, 1.73-37.3; homozygotes). Other statistically significant associations were found in subgroups defined by smoking habits (never or ex-smokers), environmental tobacco smoke or gender, with no obvious pattern. When gene variants were organized according to the three main pathways, the emerging picture was of a strong involvement of combined phase I enzymes in leukemia, with an OR of 5 (1.63-15.4) for those having three or more variant alleles. The association was considerably stronger for leukemias arising before the age of 55.

Active and passive smoking, IL6, ESR1, and breast cancer risk

We evaluated the association between smoking and risk of breast cancer in non-Hispanic white (NHW) and Hispanic or American Indian (HAI) women living in the Southwestern United States. Data on lifetime exposure to active and passive smoke data were available from 1527 NHW cases and 1601 NHW controls; 798 HAI cases and 924 HAI controls. Interleukin 6 (IL6) and Estrogen Receptor alpha (ESR1) polymorphisms were assessed in conjunction with smoking. Pack-years of smoking (>or=15) were associated with increased risk of pre-menopausal breast cancer among NHW women (OR 1.6, 95% CI 1.1-2. 4). Passive smoke increased risk of pre-menopausal breast cancer for HAI women (OR 1.9, 95% CI 1.1-3.1 everyone; OR 2.3, 95% CI 1.2-4.5 nonsmokers). HAI pre-menopausal women who were exposed to 10+ h of passive smoke per week and had the rs2069832 IL6 GG genotype had over a fourfold increased risk of breast cancer (OR 4.4, 95% CI 1.5-12.8; P for interaction 0.01). Those with the ESR1 Xba1 AA genotype had a threefold increased risk of breast cancer if they smoked>or=15 pack-years relative to non-smokers (P interaction 0.01). These data suggest that breast cancer risk is associated with active and passive smoking.

A systematic approach to analysing gene-gene interactions: polymorphisms at the microsomal epoxide hydrolase EPHX and glutathione S-transferase GSTM1, GSTT1, and GSTP1 loci and breast cancer risk

OBJECTIVE

We undertook a case-control study in an Australian Caucasian population-based sample of 1,246 cases and 664 controls to assess the roles of detoxification gene polymorphisms EPHX T>C Tyr(113)His, GSTT1 deletion, GSTM1 deletion, and GSTP1 A>G Ile(105)Val on risk of breast cancer.

METHODS

We systematically addressed the main effects and possible gene-gene interactions using unconditional logistic regression to estimate odds ratios (OR) adjusted for potential confounders and using standard model building approaches based on likelihood theory.

RESULTS

There was a decreased risk associated with the EPHX CC genotype [OR, 0.60; 95% confidence interval (95% CI), 0.43-0.84; P = 0.003], marginally significant evidence of increased risk with GSTM1 null genotype (OR, 1.21; 95% CI, 1.00-1.47; P = 0.05), but no association with GSTT1 null genotype (OR, 1.12; 95% CI, 0.86-1.45; P = 0.4) or GSTP1 (OR, 0.95; 95% CI, 0.82-1.10; P = 0.5) genotype. The full model with all interactions gave a significantly better fit than a main-effects-only model (P < 0.001), providing evidence for gene-gene interactions. The most parsimonious model included main effects for EPHX, GSTT1, and GSTM1; a two-way interaction between EPHX and GSTM1; and a three-way interaction between EPHX, GSTM1, and GSTT1. Predicted risks were greatest for women carrying deletions of both GSTT1 and GSTM1, with either the EPHX TC genotype (OR, 2.02; 95% CI, 1.19-3.45; P = 0.009) or EPHX CC genotype (OR, 3.54; 95% CI, 1.29-9.72; P = 0.14).

CONCLUSION

Detoxification gene polymorphisms may interact with each other to result in small groups of individuals at modestly increased risk. We caution against overinterpretation and suggest that pooling of similarly large studies is needed to clarify the possible role of such complex gene-gene interactions on breast cancer risk. 2007;16(4):769-74).

Cigarette smoke condensate-induced level of adenomatous polyposis coli blocks long-patch base excision repair in breast epithelial cells

Our previous studies have shown that treatment with cigarette smoke condensate (CSC) transforms normal breast epithelial cell line, MCF-10A. In the present study, the mechanism of CSC-induced transformation of breast epithelial cells was examined. We first determined whether benzo[a]pyrene (B[a]P)- and CSC-induced levels of APC are capable of inhibiting long-patch base excision repair (LP-BER) since our earlier studies had shown that an interaction of APC with DNA polymerase beta (pol-beta) blocks strand-displacement synthesis. With the use of a novel in vivo LP-BER assay, it was demonstrated that increased and decreased APC levels in different breast cancer cell lines were associated with a decrease or increase in LP-BER activity, respectively. The effect of APC on LP-BER in malignant and pre-malignant breast epithelial cell lines was produced by either overexpression or knockdown of APC. Furthermore, it was shown that the decreased LP-BER in B[a]P- or CSC-treated pre-malignant breast epithelial cells is associated with an increased level of APC and decreased cell growth. Our results suggest that the decreased growth allows cells to repair the damaged DNA before mitosis, and failure to repair damaged DNA has the potential to transform pre-malignant breast epithelial cells.

The role of cytochrome P450 enzymes in endogenous signalling pathways and environmental carcinogenesis

Some cytochrome P450 (CYP) heme-thiolate enzymes participate in the detoxication and, paradoxically, the formation of reactive intermediates of thousands of chemicals that can damage DNA, as well as lipids and proteins. CYP expression can also affect the production of molecules derived from arachidonic acid, and alters various downstream signal-transduction pathways. Such changes can be precursors to malignancy. Recent studies in mice have changed our perceptions about the function of CYP1 enzymes. We suggest a two-tiered system to predict an overall inter-individual risk of tumorigenesis based on DNA variants in certain 'early defence' CYP genes, combined with polymorphisms in various downstream target genes.

Hot flash therapies in breast cancer survivors

More than 86% of those diagnosed with invasive breast cancer are expected to survive for >/= 5 years after their diagnosis. Approximately 75% of postmenopausal women who had breast cancer report experiencing hot flashes. More than 90% of young survivors also experience hot flashes, which can be more severe and long lasting, with iatrogenic ovarian ablation or antiestrogen therapy. There are numerous options for the treatment of hot flashes. Not one treatment fits all. Some treatments are generally more effective than others, and each has different side effects. This review is meant to provide the basic information needed to make a decision about the best treatment for a breast survivor experiencing hot flashes.