Genetic Polymorphisms Involved in Insulin-like Growth Factor (IGF) Pathway in Relation to Mammographic Breast Density and IGF Levels

Genetic architecture of mammographic density as a risk factor for breast cancer: a systematic review

BACKGROUND

Mammography Density (MD) is a potential risk marker that is influenced by genetic polymorphisms and can subsequently modulate the risk of breast cancer. This qualitative systematic review summarizes the genes and biological pathways involved in breast density and discusses the potential clinical implications in view of the genetic risk profile for breast density.

METHODS

The terms related to "Common genetic variations" and "Breast density" were searched in Scopus, PubMed, and Web of Science databases. Gene pathways analysis and assessment of protein interactions were also performed.

RESULTS

Eighty-six studies including 111 genes, reported a significant association between mammographic density in different populations. ESR1, IGF1, IGFBP3, and ZNF365 were the most prevalent genes. Moreover, estrogen metabolism, signal transduction, and prolactin signaling pathways were significantly related to the associated genes. Mammography density was an associated phenotype, and eight out of 111 genes, including COMT, CYP19A1, CYP1B1, ESR1, IGF1, IGFBP1, IGFBP3, and LSP1, were modifiers of this trait.

CONCLUSION

Genes involved in developmental processes and the evolution of secondary sexual traits play an important role in determining mammographic density. Due to the effect of breast tissue density on the risk of breast cancer, these genes may also be associated with breast cancer risk.

Plasma Growth Factor Gene Expression and Mammographic Breast Density in Postmenopausal Women

Mammographic breast density (MBD) is a risk factor for breast cancer, but its molecular basis is poorly understood. Growth factors stimulate cellular and epithelial proliferation and could influence MBD via these mechanisms. Studies investigating the associations of circulating growth factors with MBD have, however, yielded conflicting results especially in postmenopausal women. We, therefore, investigated the associations of plasma growth factor gene expression (IGF-1, IGFBP-3, FGF-1, FGF-12, TGFB-1 and BMP-2) with MBD in postmenopausal women. We used NanoString nCounter platform to quantify plasma growth factor gene expression and Volpara to evaluate volumetric MBD measures. We investigated the associations of growth factor gene expression with MBD using both multiple linear regression (fold change) and multinomial logistic regression models, adjusted for potential confounders. The mean age of the 368 women enrolled was 58 years (range: 50-64). In analyses using linear regression models, one unit increase in IGF-1 gene expression was associated with a 35% higher VPD (1.35, 95%CI 1.13-1.60, p-value=0.001). There were suggestions that TGFB-1 gene expression was positively associated with VPD while BMP gene expression was inversely associated with VPD, but these were not statistically significant. In analyses using multinomial logistic regression, TGFB-1 gene expression was 33% higher (OR=1.33, 95%CI 1.13-1.56, p-value=0.0008) in women with extremely dense breasts than those with almost entirely fatty breasts. There were no associations between growth factor gene expression and dense volume or non-dense volume. Our study provides insights into the associations of growth factors with MBD in postmenopausal women and require confirmation in other study populations.

Mammographic breast density and IGF-1 gene polymorphisms rs1520220, rs2946834 and rs6219 in Polish women

Aim of the study

The aim of the study was to analyze three single nucleotide polymorphisms – rs1520220, rs2946834, rs6219 – of the IGF-1 gene in the context of breast mammographic density.

Material and methods

The research material included 202 samples of the peripheral blood of women with increased mammographic breast density and 238 samples of the epithelium from the oral mucosa of women without diagnosed pathological changes of the breast and with no family history of breast and/or ovarian cancer. The real-time polymerase chain reaction method was applied for analysis of polymorphisms.

Results

rs1520220 polymorphism was associated with increased mammographic density of the breasts. The presence of the CC genotype in the IGF-1 gene increased the risk of developing higher breast density visible in mammography by 2.43-fold. CC homozygotes (rs1520220) correlated with higher Breast Imaging-Reporting and Data System scale (3 vs. 4 and 5) (OR = 5.6; 95% CI: 1.82–16.3, p = 0.001). In the present study no relationship was detected between rs6219 and rs2946834 polymorphism and mammographic breast density.

Conclusions

The results suggest that the rs1520220 polymorphism of the IGF-1 gene plays an important role in the occurrence of increased mammographic breast density.

Single nucleotide polymorphisms of insulin-like growth factor gene and mammographic breast density

Aim of the study

To analyze six single nucleotide polymorphisms (SNPs): rs1520220, rs2945834, rs5747694, rs6214, rs6219, rs5742678. An attempt was made to assess the significance of the above IGF-1 gene polymorphisms as prognostic and predictive factors in Polish women with diagnosed increased breast mammographic density.

Material and methods

The study included women diagnosed with an increased breast mammographic density (n = 98), breast cancer (n = 135) and women as a control group (n = 60). The method used to detect polymorphisms in the IGF-1 gene was the analysis of single-stranded DNA conformation polymorphism (SSCP-PCR) and Sanger’s sequencing.

Results

In the case of rs1520220 polymorphism, the genotype CC was found to increase the risk of breast cancer (OR = 2.6 95% CI 1.01-6.5, p = 0.04). Analysis of the rs2945834 polymorphism revealed that the occurrence of the G allele reduced the risk of breast cancer, while the occurrence of the A allele increased the risk of disease almost twice (OR = 0.55 95% CI). Among women who are heterozygous in terms of rs5747694 polymorphism (TG), the risk of breast cancer is twice as high as in the control group. The SNPs in the study group did not correlate with mammographic breast density.

Conclusions

The results obtained in the course of the analysis indicate that polymorphisms rs1520220, rs2946834, rs5747694 gene IGF-1 are associated with the occurrence of breast cancer but not with increased mammographic density. Summing up, the association between the polymorphisms of IGF-1 and the risk of developing breast cancer is independent of mammographic density.

Association between the polymorphisms in MMP-2 and MMP-9 with adiposity and mammographic features

BACKGROUND

Matrix metalloproteinases (MMP)-2 and -9 may play an important role in adipogenesis and carcinogenesis. We investigated whether some polymorphisms located in these genes are associated with body adiposity and mammographic breast density, which are risk factors for breast cancer.

METHODS

Our study population included 731 premenopausal women. Multivariate generalized linear models were used to evaluate the association of polymorphisms rs243865 in MMP-2 and rs3918242, rs17576, rs2250889 and rs2274756 in MMP-9 with anthropometric factors that refer to adiposity and mammographic features (percent density, dense area and non-dense area) measured by computer-assisted method.

RESULTS

The number of copies of rs243865 T allele in MMP-2 was associated with increased means of anthropometric factors (p_trend < 0.05 for all except waist-to-hip ratio). The same allele of rs243865 was associated with decreased mean percent density (p_trend = 0.036) and increased mean non-dense area (p_trend = 0.031) when adjusted for potential confounders, but these associations were attenuated when further adjusted for adiposity.

CONCLUSION

These findings suggest that the relation between rs243865 in MMP-2 and mammographic features could be mediated by adiposity.

Response to immunohistochemical markers' conversion after neoadjuvant chemotherapy in breast cancer patients: association between imaging and histopathologic analysis

BACKGROUND

Breast ultrasound and mammography were used in the detection of residual tumor after neoadjuvant chemotherapy. The aim of this study was to evaluate the correlation between clinical and pathological responses with breast density and IHC marker conversion to understand how this information might be used in the future to direct treatment.

METHODS

We included 119 patients who underwent CNB and followed NACT. The breast density assessment was based on the mammography examination performed at the time of diagnosis. We evaluated the clinical and pathological responses to NACT by the UICC and Miller-Payne grading systems, respectively.

RESULTS

Of 119 patients who met the inclusion criteria, patients with high pre-treatment IHC markers levels showed higher expression of IHC markers regardless of the post-treatment IHC marker level at baseline. However, breast and node tumor sizes before and after NACT were negatively correlated with hormone receptor conversion and positively correlated with Ki-67 conversion (P < 0.05). Patients with low BD were more likely to have a cCR, pCR, TNBC, and postmenopausal status than those with a high BD (P < 0.05). BD was significantly associated with PR and Ki67 conversion but not ER conversion.

CONCLUSION

Our prospective observational study demonstrated that IHC marker conversion could be used to identify lesion size changes and BD. We also found that a high BD was linked to clinical and pathological responses, molecular subtype, and menopausal status. In the future, additional studies are required to validate the predictive value identified by this research.

Growth factor genes and change in mammographic density after stopping combined hormone therapy in the California Teachers Study

Background

The contribution of genetic polymorphisms to the large inter-individual variation in mammographic density (MD) changes following starting and stopping use of estrogen and progestin combined therapy (EPT) has not been well-studied. Previous studies have shown that circulating levels of insulin-like growth factors are associated with MD and cross-talk between estrogen signaling and growth factors is necessary for cell proliferation in the breast. We evaluated single nucleotide polymorphisms (SNPs) in growth factor genes in association with MD changes after women stop EPT use.

Methods

We genotyped 191 SNPs in 13 growth factor pathway genes in 284 non-Hispanic white California Teachers Study participants who previously used EPT and collected their mammograms before and after quitting EPT. Percent MD was assessed using a computer-assisted method. Change in percent MD was calculated by subtracting percent MD of an ‘off-EPT’ mammogram from percent MD of an ‘on-EPT’ (i.e. baseline) mammogram. We used multivariable linear regression analysis to investigate the association between SNPs and change in percent MD. We calculated P-values corrected for multiple testing within a gene (P_adj).

Results

Rs1983210 in INHA and rs35539615 in IGFBP1/3 showed the strongest associations. Per minor allele of rs1983210, the absolute change in percent MD after stopping EPT use decreased by 1.80% (a difference in absolute change in percent MD) (P_adj= 0.021). For rs35539615, change in percent MD increased by 1.79% per minor allele (P_adj= 0.042). However, after applying a Bonferroni correction for the number of genes tested, these associations were no longer statistically significant.

Conclusions

Genetic variation in growth factor pathway genes INHA and IGFBP1/3 may predict longitudinal MD change after women quit EPT. The observed differences in EPT-associated changes in percent MD in association with these genetic polymorphisms are modest but may be clinically significant considering that the magnitude of absolute increase in percent MD reported from large clinical trials of EPT ranged from 3% to 7%.

Electronic supplementary material

The online version of this article (10.1186/s12885-018-4981-6) contains supplementary material, which is available to authorized users.

Stromal characteristics may hold the key to mammographic density: the evidence to date

There is strong epidemiological data indicating a role for increased mammographic density (MD) in predisposing to breast cancer, however, the biological mechanisms underlying this phenomenon are less well understood. Recently, studies of human breast tissues have started to characterise the features of mammographically dense breasts, and a number of in-vitro and in-vivo studies have explored the potential mechanisms through which dense breast tissue may exert this tumourigenic risk. This article aims to review both the pathological and biological evidence implicating a key role for the breast stromal compartment in MD, how this may be modified and the clinical significance of these findings. The epidemiological context will be briefly discussed but will not be covered in detail.

Association study of IGFBP1 and IGFBP3 polymorphisms with hypertension and cardio-cerebral vascular diseases in a Chinese Han population

Previous studies have showed that insulin-like growth factor (IGF) axis is involved in the development of hypertension. It is unclear whether genetic variants in the IGF-binding proteins (IGFBPs) contribute to the susceptibility to hypertension. Three single-nucleotide polymorphisms (SNPs) in IGFBP1 and four SNPs in IGFBP3 were selected for genotyping in 2,012 hypertension cases and 2,210 healthy controls and 4,128 subjects were followed up for a median of 5.01 years. Multiple logistic regression and Cox regression were performed to evaluate the association of these seven SNPs with hypertension and cardio-cerebral vascular disease (CCVD). In the case-control study, rs2132572 and rs3110697 at IGFBP3 were significantly associated with hypertension, and the odds ratios (ORs) of rs2132572 (CT+TT vs. CC) and rs3110697 (GA+AA vs. GG) were 1.235 (P=0.002) and 1.176 (P=0.013), respectively (PFDR<0.05). The association of rs2132572 (TT vs. CT+CC) with hypertension was further replicated in the follow-up population, with a hazard ratio (HR) of 1.694 (P=0.014). rs1874479 at IGFBP1 was significantly associated with CCVD, particularly with stroke, and the HRs of the additive model were 1.310 (P=0.007) and 1.372 (P=0.015). Moreover, the hypertension cases presented with lower serum IGFBP1 levels than the controls (P=0.011). The serum levels of IGFBP1 significantly varied among the genotypes of rs1065780, rs2854843 and rs13223993, both in the controls and in the hypertension cases (P<0.05). These findings suggest that the genetic variants of IGFBP1 and IGFBP3 were associated with an increased risk of stroke and hypertension, respectively. Lower serum IGFBP1 levels may predict an increased risk of hypertension.

Insulin-like growth factor 1 gene polymorphism in women with breast cancer

Breast cancer is a disease of unknown etiology; however, the major risk factors are genetic alterations. Studies have demonstrated an association between insulin-like growth factor 1 (IGF-1) gene polymorphism and cell proliferation and reduced apoptosis, in addition to its role in breast cancer growth and aggressiveness. Two polymorphic variants of the IGF-1 gene are highlighted in association with breast cancer, rs6220 and rs7136446, although controversy exists as to this relationship. The current study included 137 women (68 breast cancer cases and 69 controls without breast cancer) who had 3 ml of peripheral blood drawn for the study of genomic DNA extracted from leukocytes using the genotyping technique by real-time polymerase chain reaction. The CC genotype (rs7136446) was present in 4 women (5.9%) from the case group and in 2 (3.0%) women from the control group (p = 0.67), while the GG genotype (rs6220) occurred in 8 (11.5%) women from the case group and in 5 (7.2%) women from the control group (p = 0.75). No statistically significant difference was observed between the CC genotype of variant rs7136446 in premenopausal case and control women (p = 0.31), thus as there was also no significant difference between case and control postmenopausal women (p = 1.00). Concerning the GG genotype of rs6220, it occurred in 6 (14.2%) premenopausal case and 4 (8%) control women (p = 0.71) and no difference was found in postmenopausal women (p = 1.00). In the current study, IGF-1 gene polymorphism of SNP variants rs6220 and rs7136446 had no statistically significant association with breast cancer, both in premenopausal and postmenopausal women.

Insulin-like growth factor-1 signaling in renal cell carcinoma

Renal cell carcinoma (RCC) incidence is highest in highly developed countries and it is the seventh most common neoplasm diagnosed. RCC management include nephrectomy and targeted therapies. Type 1 insulin-like growth factor (IGF-1) pathway plays an important role in cell proliferation and apoptosis resistance. IGF-1 and insulin share overlapping downstream signaling pathways in normal and cancer cells. IGF-1 receptor (IGF1R) stimulation may promote malignant transformation promoting cell proliferation, dedifferentiation and inhibiting apoptosis. Clear cell renal cell carcinoma (ccRCC) patients with IGF1R overexpression have 70 % increased risk of death compared to patients who had tumors without IGF1R expression. IGF1R signaling deregulation may results in p53, WT, BRCA1, VHL loss of function. RCC cells with high expression of IGF1R are more resistant to chemotherapy than cells with low expression. Silencing of IGF1R increase the chemosensitivity of ccRCC cells and the effect is greater in VHL mutated cells. Understanding the role of IGF-1 signaling pathway in RCC may result in development of new targeted therapeutic interventions. First preclinical attempts with anti-IGF-1R monoclonal antibodies or fragment antigen-binding (Fab) fragments alone or in combination with an mTOR inhibitor were shown to inhibit in vitro growth and reduced the number of colonies formed by of RCC cells.

Polymorphisms of Insulin-Like Growth Factor 1 Pathway Genes and Breast Cancer Risk

Genetic variants of insulin-like growth factor 1 (IGF1) pathway genes have been shown to be associated with breast density and IGF1 levels and, therefore, may also influence breast cancer risk via pro-survival signaling cascades. The aim of this study was to investigate associations between IGF1 pathway single nucleotide polymorphisms (SNPs) and breast cancer risk among European and East Asian women, and potential interactions with menopausal status and breast tumor subtype. Stratified analyses of 1,037 cases and 1,050 controls from a population-based case–control study were conducted to assess associations with breast cancer for 22 SNPs across 5 IGF1 pathway genes in European and East Asian women. Odds ratios were calculated using logistic regression in additive genetic models. Polytomous logistic regression was used to assess heterogeneity by breast tumor subtype. Two SNPs of the IGF1 gene (rs1019731 and rs12821878) were associated with breast cancer risk among European women. Four highly linked IGF1 SNPs (rs2288378, rs17727841, rs7136446, and rs7956547) were modified by menopausal status among East Asian women only and associated with postmenopausal breast cancers. The association between rs2288378 and breast cancer risk was also modified by breast tumor subtype among East Asian women. Several IGF1 polymorphisms were found to be associated with breast cancer risk and some of these associations were modified by menopausal status or breast tumor subtype. Such interactions should be considered when assessing the role of these variants in breast cancer etiology.

Insulin-like growth factor 1 receptor expression and IGF1R 3129G > T polymorphism are associated with response to neoadjuvant chemotherapy in breast cancer patients: results from the NEOZOTAC trial (BOOG 2010-01)

Background

The insulin-like growth factor 1 (IGF-1) pathway is involved in cell growth and proliferation and is associated with tumorigenesis and therapy resistance. This study aims to elucidate whether variation in the IGF-1 pathway is predictive for pathologic response in early HER2 negative breast cancer (BC) patients, taking part in the phase III NEOZOTAC trial, randomizing between 6 cycles of neoadjuvant TAC chemotherapy with or without zoledronic acid.

Methods

Formalin-fixed paraffin-embedded tissue samples of pre-chemotherapy biopsies and operation specimens were collected for analysis of IGF-1 receptor (IGF-1R) expression (n = 216) and for analysis of 8 candidate single nucleotide polymorphisms (SNPs) in genes of the IGF-1 pathway (n = 184) using OpenArray® RealTime PCR. Associations with patient and tumor characteristics and chemotherapy response according to Miller and Payne pathologic response were performed using chi-square and regression analysis.

Results

During chemotherapy, a significant number of tumors (47.2 %) showed a decrease in IGF-1R expression, while in a small number of tumors an upregulation was seen (15.1 %). IGF-1R expression before treatment was not associated with pathological response, however, absence of IGF-1R expression after treatment was associated with a better response in multivariate analysis (P = 0.006) and patients with a decrease in expression during treatment showed a better response to chemotherapy as well (P = 0.020). Moreover, the variant T allele of 3129G > T in IGF1R (rs2016347) was associated with a better pathological response in multivariate analysis (P = 0.032).

Conclusions

Absent or diminished expression of IGF-1R after neoadjuvant chemotherapy was associated with a better pathological response. Additionally, we found a SNP (rs2016347) in IGF1R as a potential predictive marker for chemotherapy efficacy in BC patients treated with TAC.

Trial registration

ClinicalTrials.gov NCT01099436. Registered April 6, 2010.

Mutational analysis of the insulin-like growth factor 1 receptor tyrosine kinase domain in non-small cell lung cancer patients

The insulin-like growth factor 1 receptor (IGF1R) pathway plays an important role in the pathogenesis of non-small cell lung cancer (NSCLC) and also provides a mechanism of resistance to targeted therapies. IGF1R is therefore an ideal therapeutic target and several inhibitors have entered clinical trials. However, thus far the response to these inhibitors has been poor, highlighting the importance of predictive biomarkers to identify patient cohorts who will benefit from these targeted agents. It is well-documented that mutations and/or deletions in the epidermal growth factor receptor (EGFR) tyrosine kinase (TK) domain predict sensitivity of NSCLC patients to EGFR TK inhibitors. Single-nucleotide polymorphisms (SNPs) in the IGF pathway have been associated with disease, including breast and prostate cancer. The aim of the present study was to elucidate whether the IGF1R TK domain harbours SNPs, somatic mutations or deletions in NSCLC patients and correlates the mutation status to patient clinicopathological data and prognosis. Initially 100 NSCLC patients were screened for mutations/deletions in the IGF1R TK domain (exons 16-21) by sequencing analysis. Following the identification of SNP rs2229765, a further 98 NSCLC patients and 866 healthy disease-free control patients were genotyped using an SNP assay. The synonymous SNP (rs2229765) was the only aberrant base change identified in the IGF1R TK domain of 100 NSCLC patients initially analysed. SNP rs2229765 was detected in exon 16 and was found to have no significant association between IGF1R expression and survival. The GA genotype was identified in 53.5 and 49.4% of NSCLC patients and control individuals, respectively. No significant difference was found in the genotype (P=0.5487) or allele (P=0.9082) frequencies between the case and control group. The present findings indicate that in contrast to the EGFR TK domain, the IGF1R TK domain is not frequently mutated in NSCLC patients. The synonymous SNP (rs2229765) had no significant association between IGF1R expression and survival in the cohort of NSCLC patients.

Mammographic breast density: Predictive value for pathological response to neoadjuvant chemotherapy in breast cancer patients

BACKGROUND

This study aims to evaluate the relation between mammographic breast density (BD) and pathological response to neoadjuvant chemotherapy.

METHODS

In this retrospective study, 241 breast cancer patients who received neoadjuvant chemotherapy were included. BD was assessed in mammograms already performed at diagnosis. Pathological complete response (pCR) and pathological stage were correlated with BD, tumour phenotype and other clinico-pathological factors.

RESULTS

Patients with low BD had better pCR compared to those with high density (30.5% vs 19.5% respectively, OR = 1.8, 95% CI = 0.98-3.3, p = 0.056) which was more pronounced after adjustment with body mass index (BMI) (OR = 2.4, 95% CI = 1.2-4.8, p = 0.011). HER2-positive disease (32.5% vs. 18.4%, OR = 2.2, 95% = 1.2-4.0, p = 0.01), lower BMI (OR = 1.1, 95% CI = 1.03-1.15, p = 0.004) and lower clinical stage (p = 0.002) were significant predictors of pCR in univariate analysis. In multivariate analysis, low BD (OR = 2.7, 95% CI = 1.3-5.5, p = 0.006) and lower BMI (OR = 1.1, 95% CI = 1.03-1.17, p = 0.003) were independent predictors of better pCR, while early clinical stage (I, II) was of borderline significance (OR = 2.6, 95% CI = 0.99-6.7, p = 0.052). High BD (OR = 1.8, 95% CI = 1.1-3.2, p = 0.03), advanced clinical stage (III) (OR = 1.5, 95% CI = 1.03-2.1, p = 0.03) and higher BMI (OR = 1.06, 95% CI = 1.02-1.11, p = 0.006) were significant predictors of advanced pathological stage.

CONCLUSION

Low mammographic BD, low BMI and early clinical stage were associated with improved pCR rate and lower pathological stage after neoadjuvant chemotherapy. BD had more pronounced association with response to chemotherapy after adjustment with BMI.

Association between germline single nucleotide polymorphisms in the PI3K-AKT-mTOR pathway, obesity, and breast cancer disease-free survival

Obesity-related hormones and cytokines alter PI3 K-AKT-mTOR pathway activation in breast tumors contributing to poorer disease-free survival (DFS) and decreased responsiveness to tamoxifen and trastuzumab. We hypothesized that single nucleotide polymorphisms (SNPs) in candidate genes in the PI3 K-AKT-mTOR signaling pathway may act as genetic modifiers of breast cancer DFS. We analyzed the association of 106 tagging SNPs in 13 genes (ADIPOQ, IGF1, INS, IRS1, LEP, LEPR, LEPROT, PIK3CA, PIK3R5, PTEN, TSC1, TSC2, and AKT1) in the P13K-AKT-mTOR pathway with DFS in a sample of 1,019 women with stage I-II breast cancer. SNPs significantly associated with DFS in any genetic model (additive, dominant, or recessive) after correcting for false discovery rate (FDR = 0.10) were included in Cox proportional hazards multivariable analyses. After adjusting for race/ethnicity, age at diagnosis, tumor stage, and treatment, rs1063539 in ADIPOQ, rs11585329 in LEPR, and rs2519757 in TSC1 were associated with improved DFS, and rs1520220 in IGF1 and rs2677760 in PIK3CA were associated with worse DFS. The associations were not significantly modified by the type of systemic treatment received or body mass index. The SNPs were not associated with tumor characteristics such as tumor size, lymph node status, nuclear grade, or hormone receptor status. In this study, germline SNPs in the PI3 K-AKT-mTOR pathway were associated with breast cancer DFS and may be potential prognostic markers. Future studies are needed to replicate our results and to evaluate the relationship between these polymorphisms and activation of the PI3 K-AKT-mTOR pathway in breast tumors.

Mammographic density-a review on the current understanding of its association with breast cancer

There has been considerable recent interest in the genetic, biological and epidemiological basis of mammographic density (MD), and the search for causative links between MD and breast cancer (BC) risk. This report will critically review the current literature on MD and summarize the current evidence for its association with BC. Keywords 'mammographic dens*', 'dense mammary tissue' or 'percent dens*' were used to search the existing literature in English on PubMed and Medline. All reports were critically analyzed. The data were assigned to one of the following aspects of MD: general association with BC, its relationship with the breast hormonal milieu, the cellular basis of MD, the generic variations of MD, and its significance in the clinical setting. MD adjusted for age, and BMI is associated with increased risk of BC diagnosis, advanced tumour stage at diagnosis and increased risk of both local recurrence and second primary cancers. The MD measures that predict BC risk have high heritability, and to date several genetic markers associated with BC risk have been found to also be associated with these MD risk predictors. Change in MD could be a predictor of the extent of chemoprevention with tamoxifen. Although the biological and genetic pathways that determine and perhaps modulate MD remain largely unresolved, significant inroads are being made into the understanding of MD, which may lead to benefits in clinical screening, assessment and treatment strategies. This review provides a timely update on the current understanding of MD's association with BC risk.

Insulin-like growth factor receptor polymorphism defines clinical outcome in estrogen receptor-positive breast cancer patients treated with tamoxifen

Compelling evidence points to a key role for insulin-like growth factor 1 (IGF1) signaling in breast cancer development and progression. In addition, IGF1 receptor (IGF1R) expression has been correlated and functionally linked with estrogen receptor (ER) signaling. Recent translational studies support a cross talk between IGF1R and ERα at different levels and data suggest enhanced IGF1R signaling as a causative mechanism of tamoxifen (TAM) resistance. We tested whether functional germline variations in the IGF pathway are associated with clinical outcome in ER-positive primary invasive breast cancer patients, who were treated with surgery and adjuvant TAM. Tissue samples of 222 patients with ER+ primary invasive breast cancer, who had undergone surgery at Charing Cross Hospital, London, UK between 1981 and 2003, were analyzed. Genomic DNA was extracted from formalin-fixed, paraffin-embedded tissue samples and six functional IGF1 pathway polymorphisms were analyzed using direct DNA sequencing and PCR-restriction fragment length polymorphism. In multivariable analysis, patients with primary invasive breast cancer carrying IGF1R_rs2016347 G allele had a significantly increased risk of early tumor progression (hazard ratio (HR) 2.01; adjusted P=0.004) and death (HR 1.84; adjusted P=0.023) compared with patients carrying G/T or T/T, independent of established clinicopathological determinants. This association remained significant after adjusting for multiple testing. In addition, we were able to demonstrate that IRS1_rs1801123 and IGFBP3_rs2854744 were significantly associated with lymph node involvement and tumor size, respectively. We provide the first evidence for IGF1R_rs2016347 as an independent prognostic marker for ER+ breast cancer patients treated with TAM and support a rational for combined treatment strategies.

Does mammographic density reflect the expression of breast cancer markers?

Mammographic density reflects variation in breast tissue composition as detected on mammogram. It is associated with a number of well-known breast cancer risk factors and itself is considered one of the strongest risk factors for breast cancer. If the expression of several proteins and genes within the breast tissue influences mammographic density in the same way as it influences breast cancer risk, then mammographic density might serve as an intermediate biomarker in future epidemiological studies on breast cancer. This has the potential to provide a quick means for predicting the effect of changes in the breast microenvironment on breast cancer risk without having to wait for an eventual development of breast cancer. In this review, the expression of several proteins and genes (growth factors, enzymes, proteoglycans and pro-inflammatory markers) within the breast tissue is shown to be associated with mammographic density. These proteins and genes are suspected to play a role in breast carcinogenesis. More studies assessing differential expression of proteins and genes in mammary epithelium and stroma and their association with mammographic density among premenopausal and postmenopausal women are required. Identification of proteins and genes influencing mammographic density may provide further insight on the molecular causes of breast cancer.

Common variants in IGF1 pathway genes and clinical outcomes after radical prostatectomy

BACKGROUND

Insulin-like growth factor-1 (IGF1) pathway plays a critical role in malignant transformation, and epidemiology studies have also shown that single nucleotide polymorphisms (SNPs) in IGF1 pathway genes are associated with prostate cancer risk. However, the clinical significance of these SNPs on prostate cancer aggressiveness and prognosis after radical prostatectomy (RP) has not been determined.

METHODS

We evaluated the associations of 4 common SNPs in IGF1 and IGF1R with age at diagnosis, preoperative prostate-specific antigen (PSA) level, pathologic Gleason score, pathologic stage, surgical margin, lymph node metastasis, and PSA recurrence in a cohort of 320 localized prostate cancer patients receiving RP. The prognostic significance on time to PSA recurrence was also assessed by Cox proportional hazards model.

RESULTS

IGF1 rs2946834 alleles/genotypes and an IGF1 specific haplotype AT, containing the minor allele of rs2946834, were associated (P ≤ 0.028) with a 1.49- to 2.22-fold higher risk of having advanced-stage prostate cancer. In addition, a genetic interaction profile consisting of IGF1 rs2946834 and IGF1R rs2016347 was significantly associated with PSA recurrence (P = 0.033).

CONCLUSIONS

Our study is the first to evaluate the impact of SNPs in IGF1 pathway genes on PSA recurrence. A genetic interaction between IGF1 rs2946834 and IGF1R rs2016347 might be a predictor of outcomes following RP.

Diabetes and cancer II: role of diabetes medications and influence of shared risk factors

An association between type 2 diabetes mellitus (DM) and cancer has long been postulated, but the biological mechanism responsible for this association has not been defined. In part one of this review, we discussed the epidemiological evidence for increased risk of cancer, decreased cancer survival, and decreased rates of cancer screening in diabetic patients. Here we review the risk factors shared by cancer and DM and how DM medications play a role in altering cancer risk. Hyperinsulinemia stands out as a major factor contributing to the association between DM and cancer, and modulation of circulating insulin levels by DM medications appears to play an important role in altering cancer risk. Drugs that increase circulating insulin, including exogenous insulin, insulin analogs, and insulin secretagogues, are generally associated with an increased cancer risk. In contrast, drugs that regulate insulin signaling without increasing levels, especially metformin, appear to be associated with a decreased cancer risk. In addition to hyperinsulinemia, the effect of DM medications on other shared risk factors including hyperglycemia, obesity, and oxidative stress as well as demographic factors that may influence the use of certain DM drugs in different populations are described. Further elucidation of the mechanisms behind the association between DM, cancer, and the role of DM medications in modulating cancer risk may aid in the development of better prevention and treatment options for both DM and cancer. Additionally, incorporation of DM medication use into cancer prediction models may lead to the development of improved risk assessment tools for diabetic patients.

Insulin-like growth factor axis gene polymorphisms modify risk of pancreatic cancer

OBJECTIVE

Insulin-like growth factor (IGF)-axis genes plays a critical role in cancer development and progression via their impact on the RAS/MAPK/ERK and PI3K/AKT/mTOR signaling pathways. We hypothesized that IGF-axis genetic variants modify individual susceptibility to pancreatic cancer.

METHODS

We retrospectively genotyped 41 single-nucleotide polymorphisms of 10 IGF-axis genes (IGF1, IGF2, IGF1R, IGF2R, IGFBP1, IGFBP3, IGFBP5, IRS1, IRS2, and IRS4) in 706 pancreatic cancer patients and 706 cancer-free controls using Sequenom and TaqMan technology. The association between genotype and pancreatic cancer risk was evaluated using multivariate logistic regression. A P value ≤.007 at a false discovery rate of 10% was set as the significance level.

RESULTS

We observed that the IGF1 *10212C>A and Ex4+2776G>A and IGF1R IVS2-70184A>G and IVS2+46329T>C variant genotypes were significantly associated with decreased pancreatic cancer risk (odds ratio [OR] range, 0.60-0.75) and that IGFBP1 Ex4+111A>G (I253M) was significantly associated with increased pancreatic cancer risk (OR=1.46) after adjusted for other risk factors and multiple comparisons (P≤.007). IGF2R and IGFBP3 variant haplotypes were associated with increased and decreased pancreatic cancer risk, respectively (P<.001). We also observed a weak interaction of the IGF1R IVS2+46329T>C and IGF2R Ex45+11C>T (L2222L) genotypes with diabetes (P(interaction)=.05) and interaction of IGF2R and IRS1 genotypes with alcohol consumption (P(interaction)=.03 and .019, respectively) on increased pancreatic cancer risk.

CONCLUSION

These findings support our hypothesis that polymorphic variants of IGF-axis genes act alone or jointly with other risk factors to affect susceptibility to pancreatic cancer.

Genetic variants, prediagnostic circulating levels of insulin-like growth factors, insulin, and glucose and the risk of colorectal cancer: the Multiethnic Cohort study

BACKGROUND

Increased exposure of colonic and rectal epithelial cells to the promitotic and antiapoptotic effects of insulin and insulin-like growth factors (IGF) is hypothesized to increase colorectal cancer risk.

METHODS

In a case-control study nested within the Multiethnic Cohort, we attempted to replicate associations for five genetic variants associated with IGF system biomarkers, insulin, or glucose and to examine their association with the risk of colorectal cancer. In a subset of participants, the association between circulating biomarkers and colorectal cancer risk was examined. Unconditional logistic regression was used to calculate ORs and 95% confidence intervals (CI) for genetic variants (1,954 cases/2,587 controls) and serum biomarkers (258 cases/1,701 controls).

RESULTS

Associations with circulating biomarkers were replicated in the Multiethnic Cohort for IGF1 rs35767 and for IGFBP3 rs2854744, rs2854746, and rs3110697 (P < 0.05). Homozygous carriers of the glucokinase regulator (GCKR) rs780094 variant T-allele were at a decreased risk of colorectal cancer (OR, 0.77; 95% CI, 0.64-0.92). In risk factor-adjusted models, participants with the highest prediagnostic IGF-II levels were at an increased risk [OR (T1 vs. T3), 1.58; 95% CI, 1.09-2.28; P(trend) = 0.011] and participants with the highest prediagnostic IGF-binding protein (IGFBP)-3 levels were at a decreased risk of colorectal cancer (OR, 0.53; 95% CI, 0.34-0.83; P(trend) = 0.003).

CONCLUSION

These data provide further support for a role of prediagnostic IGF and insulin levels in the etiology of colorectal cancer.

IMPACT

Future studies attempting to replicate the association between the GCKR rs780094 variant and the risk of colorectal cancer are warranted.

Genetic and environmental predictors, endogenous hormones and growth factors, and risk of estrogen receptor-positive breast cancer in Japanese women

The incidence of breast cancer in Japanese women has doubled in all age groups over the past two decades. We have recently shown that this marked increase is mostly due to an increase in the estrogen receptor (ER)-positive subtype. It is necessary to establish risk factors capable of predicting the risk of ER-positive breast cancer that will enable the efficient selection of candidates for preventive therapy. We analyzed genetic factors, including 14 single nucleotide polymorphisms (SNPs), environmental risk factors (body mass index, age at menarche, pregnancy, age at first birth, breastfeeding, family history of breast cancer, age at menopause, use of hormone replacement therapy, alcohol intake, and smoking), serum hormones and growth factors (estradiol, testosterone, prolactin, insulin-like growth factor 1 [IGF1] and IGF binding protein 3 [IGFBP3]), and mammographic density in 913 women with breast cancer and 278 disease-free controls. To identify important risk factors, risk prediction models for ER-positive breast cancer in both pre- and postmenopausal women were created by logistic regression analysis. In premenopausal women, one SNP (CYP19A1-rs10046), age, pregnancy, breastfeeding, alcohol intake, serum levels of prolactin, testosterone, and IGFBP3 were considered to be risk predictors. In postmenopausal women, one SNP (TP53-rs1042522), age, body mass index, age at menopause, serum levels of testosterone, and IGF1 were identified as risk predictors. Risk factors may differ between women of different menopausal status, and inclusion of common genetic variants and serum hormone measurements as well as environmental factors might improve risk assessment models. Further validation studies will clarify appropriate risk groups for preventive therapy.

Visceral adiposity, insulin resistance and cancer risk

BACKGROUND

There is a well established link between obesity and cancer. Emerging research is characterising this relationship further and delineating the specific role of excess visceral adiposity, as opposed to simple obesity, in promoting tumorigenesis. This review summarises the evidence from an epidemiological and pathophysiological perspective.

METHODS

Relevant medical literature was identified from searches of PubMed and references cited in appropriate articles identified. Selection of articles was based on peer review, journal and relevance.

RESULTS

Numerous epidemiological studies consistently identify increased risk of developing carcinoma in the obese. Adipose tissue, particularly viscerally located fat, is metabolically active and exerts systemic endocrine effects. Putative pathophysiological mechanisms linking obesity and carcinogenesis include the paracrine effects of adipose tissue and systemic alterations associated with obesity. Systemic changes in the obese state include chronic inflammation and alterations in adipokines and sex steroids. Insulin and the insulin-like growth factor axis influence tumorigenesis and also have a complex relationship with adiposity. There is evidence to suggest that insulin and the IGF axis play an important role in mediating obesity associated malignancy.

CONCLUSIONS

There is much evidence to support a role for obesity in cancer progression, however further research is warranted to determine the specific effect of excess visceral adipose tissue on tumorigenesis. Investigation of the potential mechanisms underpinning the association, including the role of insulin and the IGF axis, will improve understanding of the obesity and cancer link and may uncover targets for intervention.

A randomized, placebo-controlled trial (NCIC CTG MAP.2) examining the effects of exemestane on mammographic breast density, bone density, markers of bone metabolism and serum lipid levels in postmenopausal women

We hypothesized that exemestane (EXE) would reduce mammographic breast density and have unique effects on biomarkers of bone and lipid metabolism. Healthy postmenopausal women were randomized to EXE (25 mg daily) or placebo (PLAC) for 12 months and followed for a total of 24 months. The primary endpoint was change in percent breast density (PD) between the baseline and 12-month mammograms and secondary endpoints were changes in serum lipid levels, bone biomarkers, and bone mineral density (BMD). Ninety-eight women were randomized (49 to EXE; 49 to PLAC) and 65 had PD data at baseline and 12 months. Among women treated with EXE, PD was not significantly changed from baseline at 6, 12, or 24 months and was not different from PLAC. EXE was associated with significant percentage increase from baseline in N-telopeptide at 12 months compared with PLAC. No differences in percent change from baseline in BMD (lumbar spine and femoral neck) were observed between EXE and PLAC at either 12 or 24 months. Patients on EXE had a significantly larger percent decrease in total cholesterol than in the PLAC arm at 6 months and in HDL cholesterol at 3, 6, and 12 months. No significant differences in percent change in LDL or triglycerides were noted at any time point between the two treatment arms. EXE administered for 1 year to healthy postmenopausal women did not result in significant changes in mammographic density. A reversible increase in the bone resorption marker N-telopeptide without significant change in bone specific alkaline phosphatase or BMD during the 12 months treatment period and 1 year later was noted. Changes in lipid parameters on this trial were modest and reversible.

Role of the growth hormone-IGF-1 axis in cancer

A substantial body of evidence supports a role for the growth hormone (GH)-IGF-1 axis in cancer incidence and progression. This includes epidemiological evidence relating elevated plasma IGF-1 to cancer incidence as well as a lack of cancers in GH/IGF-1 deficiency. Rodent models lacking GH or its receptor are strikingly resistant to the induction of a wide range of cancers, and treatment with the GH antagonist pegvisomant slows tumor progression. While GH receptor expression is elevated in many cancers, autocrine GH is present in several types, and overexpression of autocrine GH can induce cell transformation. While the mechanism of autocrine action is not clear, it does involve both STAT5 and STAT3 activation, and probably nuclear translocation of the GH receptor. Development of a more potent GH receptor antagonist or secretion inhibitor is warranted for cancer therapy.

IGFBP1 and IGFBP3 polymorphisms predict circulating IGFBP-3 levels among women from high-risk breast cancer families

The insulin-like growth factor (IGF) pathway has been implicated as risk modifier in premenopausal breast cancer. In this study, associations between single nucleotide polymorphisms (SNPs) and diplotypes in the IGFBP1 and IGFBP3 genes and circulating IGFBP-3 levels, BRCA family status and breast cancer among women from high-risk breast cancer families were investigated. Nine IGFBP1 and IGFBP3 SNPs were genotyped with PCR-based methods in 323 women. Nine IGFBP1 and ten IGFBP3 diplotypes were identified. Plasma IGFBP-3 levels obtained during cycle day 18-23 were available for 231 women, 87 current users of combined oral contraceptives and 144 non-users. IGFBP1 (rs1995051 and rs4988515) and IGFBP3 (rs2471551 and rs2854744) SNPs were associated with circulating IGFBP-3 levels (P < 0.05). IGFBP1 (low) diplotypes were associated with lower IGFBP-3 levels and were more common in BRCA2 families OR 2.05 (95%CI 0.97-4.30). IGFBP3 (high) diplotypes were associated with higher IGFBP-3 levels and were more common in BRCAX families OR 1.68 (95%CI 1.04-2.74). After adjusting the models for BRCA family status, both the BRCA1 and BRCA2 family status (P ≤ 0.006) and the IGFBP1 diplotype GTAC/ACAT (P = 0.004) were associated with lower IGFBP-3 levels. Similarly, both the BRCA1 and BRCA2 family status (P ≤ 0.03) and the IGFBP-3 diplotypes GCA/GCG (P = 0.007) and GCG/CCG (P = 0.002) were significantly associated with lower IGFBP-3 levels, adjusted for age, weight, OC use, and other IGFBP diplotypes. No individual SNP was associated with breast cancer. There were 23 cases of breast cancer and one IGFBP1 diplotype was associated with a decreased risk of breast cancer after age 18 (log rank P=0.05). In conclusion, independent effects from IGFBP1, IGFBP3 diplotypes, and BRCA family status on IGFBP-3 levels were observed. These factors may influence the risk of breast cancer among women from high-risk breast cancer families.

Polymorphisms in genes involved in the estrogen pathway and mammographic density

Background

Single nucleotide polymorphisms (SNPs) in genes involved in the estrogen pathway appear to be associated with breast cancer risk and possibly with mammographic density (MD), but little is known of these associations among premenopausal women. This study examines the association of 11 polymorphisms in five estrogen-related genes (estrogen receptors alpha and beta (ERα, ERβ), 17β-hydroxysteroid dehydrogenase 1 (HSD17B1), catechol-O-methyltransferase (COMT), cytochrome P450 1B1 (CYP1B1)) with premenopausal MD. Effect modification of four estrogen-related factors (parity, age at menarche, hormonal derivatives use and body mass index (BMI)) on this relation is also assessed.

Methods

Polymorphisms were genotyped in 741 premenopausal Caucasian women whose MD was measured in absolute density (AD, cm²) and percent density using a computer-assisted method. Multivariate linear models were used to examine the associations (P_trend) and interactions (P_i).

Results

None of the SNPs showed a statistically significant association with AD. However, each additional rare allele of rs1056836 CYP1B1 was associated with a reduction in AD among nulliparous women (P_trend = 0.004), while no association was observed among parous women (P_trend = 0.62; P_i = 0.02). An increase in the number of rare alleles of the HSD17B1 SNP (rs598126 and rs2010750) was associated with an increase in AD among women who never used hormonal derivatives (P_trend = 0.06 and P_trend = 0.04, respectively), but with a decrease in AD among past hormonal derivatives users (P_trend = 0.04; P_i = 0.02 and P_trend = 0.08; P_i = 0.01, respectively). Moreover, a negative association of rs598126 HSD17B1 SNP with AD was observed among women with higher BMI (>median) (P_trend = 0.01; P_i = 0.02). A negative association between an increased number of rare alleles of COMT rs4680 SNP and AD was limited to women who never used hormonal derivatives (P_trend = 0.02; P_i = 0.03) or with late age at menarche (>median) (P_trend = 0.03; P_i = 0.02). No significant association was observed between polymorphisms in the ERα or ERβ genes and AD. Similar results, although less significant, were observed when MD was assessed in percent density.

Conclusion

SNPs located in CYP1B1, COMT or HSD17B1 genes seem to be associated with MD in some strata of estrogen-related factors. Our findings suggest that modifying effects of estrogen-related factors should be considered when evaluating associations of polymorphisms in estrogen-related genes with premenopausal mammographic density.

Germline polymorphisms in genes involved in the IGF1 pathway predict efficacy of cetuximab in wild-type KRAS mCRC patients

PURPOSE

The insulin-like growth factor 1 (IGF1) signaling pathway is an important growth-regulatory pathway, which plays a crucial role in colorectal cancer (CRC) proliferation, differentiation, migration, angiogenesis, and apoptosis. Previous studies showed that hyperactivation of the IGF1 receptor (IGF1R) may result in resistance to anti-epidermal growth factor receptor-targeted treatment. We tested whether germline variations within the IGF1 pathway are associated with clinical outcome in wild-type (wt) KRAS drug-refractory metastatic CRC (mCRC) patients who were treated with cetuximab monotherapy (IMC-0144).

EXPERIMENTAL DESIGN

Formalin-fixed, paraffin-embedded (FFPE) tissue samples of 130 drug-refractory mCRC patients enrolled in IMC-0144, a phase II clinical trial of cetuximab monotherapy, were analyzed. gDNA was extracted from dissected FFPE tumor tissue, and KRAS mutation status and six potentially functional IGF1 and IGF1R polymorphisms were analyzed using direct DNA sequencing or PCR-RFLP. Tumor response analysis was based on recursive partitioning, and survival analyses were based on univariate and multivariate hazard regression models.

RESULTS

In univariate and multivariate analyses, five IGF pathway single-nucleotide polymorphisms were significantly associated with progression-free survival (PFS) and/or overall survival (OS). In multivariate combined risk allele analysis, the additive model for PFS and OS was significantly associated with the number of risk alleles in wt KRAS patients (P = 0.001 and P = 0.02, respectively). In addition, wt KRAS patients harboring IGF1 rs2946834 A/A genotype had a 50% objective response rate compared with 0% for A/G genotype.

CONCLUSIONS

These results indicate that IGF1 pathway polymorphisms are potential predictive/prognostic molecular markers for cetuximab efficacy in wt KRAS mCRC patients. Prospective biomarker-embedded clinical trials are warranted to validate our findings. Clin Cancer Res; 16(22); 5591-602. ©2010 AACR.

IGF1, IGFBP1, and IGFBP3 genes and mammographic density: the Multiethnic Cohort

Insulin-like growth factor-I (IGF-I) has mitogenic properties and stimulates cell growth. In this analysis, we investigated the relation between common genetic variation in IGF1, IGFBP1, and IGFBP3, and mammographic density among 819 women of Hawaiian, European, and Japanese ancestry from the Multiethnic Cohort Study. Mammographic density was assessed using a quantitative computer-assisted method. Previously identified tag single nucleotide polymorphisms (SNPs) for IGF1 (26 tag SNPs) and IGFBP1/IGFBP3 (22 tag SNPs) were genotyped among the 819 women. Mixed models were conducted to evaluate the associations between genetic variation and mammographic density. Two SNPs were borderline statistical significantly associated with mammographic density: rs35539615 on IGFBP1 (p = 0.05) and rs2453839 on IGFBP3 (p = 0.01). Rs35767on IGF1 (p = 0.03) was also associated with mammographic density, although in opposite direction of what was expected from previous findings with IGF-I levels. The majority of SNPs were, however, not associated with mammographic density. Analyses stratified by ethnicity showed similar results as the overall analyses for IGF1 and IGFBP1. However, for 4 SNPs in the IGFBP3 gene, the minor allele was associated with lower mammographic density in Japanese Americans and higher mammographic density in Caucasians. Given the large number of SNPs tested and the few borderline significant results, we only found weak evidence that genetic variations in IGFBP1 or IGFBP3 may be related to mammographic density. Ethnicity may modify these relations.

Obesity, hyperinsulinemia and breast cancer: novel targets and a novel role for metformin

The relationship between obesity, metabolic syndrome, diabetes and cancer has been recognized for many years. Multiple studies conducted in the last 20 years have identified molecular mechanisms responsible for this phenomenon. Elucidation of the important role of insulin, IGF receptor, mTOR and AMP-activated protein kinase in breast cancer biology has led to the development and subsequent clinical evaluation of novel targeted therapies, including IGF-1 receptor-specific antibodies or tyrosine kinase inhibitors and inhibitors of mTOR. There is also a growing interest in the use of metformin, which has been shown to possess antitumor activity resulting from activation of AMP-activated protein kinase and subsequent inhibiton of mTOR, as well as from decreased circulating insulin levels. Metformin has been shown to inhibit proliferation, invasion and angiogenesis of neoplastic cells and to overcome resistance of breast cancer to chemotherapy, hormonal therapy and HER2 inhibition. Recently, metformin has been demonstrated to inhibit breast cancer stem cell growth and to synergize with chemotherapy in suppression of tumor growth and prolongation of survival of breast tumor-bearing animals. Several currently ongoing Phase II and III clinical studies are evaluating the therapeutic efficacy of metformin in the treatment of early and advanced breast cancer patients.

Genetic dissection of intermediate phenotypes as a way to discover novel cancer susceptibility alleles

The availability of affordable genome-wide association (GWA) studies has led to the discovery of a large number of cancer risk alleles. The prospects of identifying additional alleles using the same disease-based approach are limited unless very large samples sizes are used in future investigations. An alternative and powerful way to identify additional cancer genes is to study intermediate phenotypes, such as variation in DNA repair capacity, that are known to be associated with increased disease risk. Most of these phenotypes are highly genetic. Their measurement can be achieved using well-established medium-throughput to high-throughput methods and their genetic mapping can be carried out with relatively small sample sizes. The genetic variants associated with these phenotypes will represent ideal functionally validated candidates for cancer susceptibility studies. Unlike hypothesis-free and disease-based GWA-discovered alleles, intermediate phenotype alleles that mediate cancer risk will have a strong biological relevance and will represent excellent modifiable or 'drugable' therapeutic targets.

Genotypes and haplotypes in the insulin-like growth factors, their receptors and binding proteins in relation to plasma metabolic levels and mammographic density

BACKGROUND

Increased mammographic density is one of the strongest independent risk factors for breast cancer. It is believed that one third of breast cancers are derived from breasts with more than 50% density. Mammographic density is affected by age, BMI, parity, and genetic predisposition. It is also greatly influenced by hormonal and growth factor changes in a woman's life cycle, spanning from puberty through adult to menopause. Genetic variations in genes coding for hormones and growth factors involved in development of the breast are therefore of great interest. The associations between genetic polymorphisms in genes from the IGF pathway on mammographic density and circulating levels of IGF1, its binding protein IGFBP3, and their ratio in postmenopausal women are reported here.

METHODS

Samples from 964 postmenopausal Norwegian women aged 55-71 years were collected as a part of the Tromsø Mammography and Breast Cancer Study. All samples were genotyped for 25 SNPs in IGF1, IGF2, IGF1R, IGF2R, IGFALS and IGFBP3 using Taqman (ABI). The main statistical analyses were conducted with the PROC HAPLOTYPE procedure within SAS/GENETICS (SAS 9.1.3).

RESULTS

The haplotype analysis revealed six haploblocks within the studied genes. Of those, four had significant associations with circulating levels of IGF1 or IGFBP3 and/or mammographic density. One haplotype variant in the IGF1 gene was found to be associated with mammographic density. Within the IGF2 gene one haplotype variant was associated with levels of both IGF1 and IGFBP3. Two haplotype variants in the IGF2R were associated with the level of IGF1. Both variants of the IGFBP3 haplotype were associated with the IGFBP3 level and indicate regulation in cis.

CONCLUSION

Polymorphisms within the IGF1 gene and related genes were associated with plasma levels of IGF1, IGFBP3 and mammographic density in this study of postmenopausal women.

Common genetic variation of insulin-like growth factor-binding protein 1 (IGFBP-1), IGFBP-3, and acid labile subunit in relation to serum IGF-I levels and mammographic density

Mammographic density is strongly related to increased breast cancer risk. Accumulating evidence indicates that a role for the IGF-pathway in mammographic density and breast cancer development. Here, we investigate whether common genetic variation in this pathway influences insulin-like growth factor-I (IGF-I) levels and mammographic density. In 1,916 premenopausal women within the Prospect-EPIC cohort, we examined associations of 14 haplotype tagging SNPs in the ALS, IGFBP1, and IGFBP3 genes with IGF-I circulating levels and mammographic density. In 657 women, who became postmenopausal during follow-up, we investigated how these SNPs were related with the decrease in density over menopause. Linear regression models were used for statistical analysis. None of the ALS or IGFBP3 SNPs were statistically significantly associated with IGF-I levels or mammographic density. The CC genotype for rs1908751 (IGFBP1) was associated with lower levels of IGF-I (110.9 ng/ml) compared to the CT/TT genotypes (115.7 ng/ml) (P = 0.04). Women with the CC genotype also had lower percent density, although not statistically significantly (P = 0.12). Women carrying the AA genotype for rs1995051 (IGFBP1) showed that borderline significantly lower IGF-I levels (P = 0.06) and significantly lower mammographic density (40.3% compared to 43.5% in the GG/GA genotypes; P = 0.05). No relationships were found for any of the SNPs in relation with changes in breast density over menopause. These findings suggest that common genetic variation in the IGFBP1 gene is weakly related to IGF-I levels and mammographic density. Our results do not provide support for such a role of genetic variants in the IGFBP3 and ALS genes.

Genetic variation and circulating levels of IGF-I and IGFBP-3 in relation to risk of proliferative benign breast disease

Insulin-like growth factor-I (IGF-I) and its major binding protein IGFBP-3 have been implicated in breast carcinogenesis. We examined the associations between genetic variants and circulating levels of IGF-I and IGFBP-3 with proliferative benign breast disease (BBD), a marker of increased breast cancer risk, in the Nurses' Health Study II (NHSII). Participants were 359 pathology-confirmed proliferative BBD cases and 359 matched controls. Circulating IGF-I and IGFBP-3 levels were measured in blood samples collected between 1996 and 1999. Thirty single nucleotide polymorphisms (SNPs) in IGF-I, IGFBP-1, and IGFBP-3 genes were selected using a haplotype tagging approach and genotyped in cases and controls. Circulating IGF-I levels were not associated with proliferative BBD risk. Higher circulating IGFBP-3 levels were significantly associated with increased risk of proliferative BBD (highest vs. lowest quartile odds ratio (OR) [95% confidence interval (CI)], 1.70 (1.06-2.72); p-trend = 0.03). The minor alleles of 2 IGFBP-3 SNPs were associated with lower proliferative BBD risk (homozygous variant vs. homozygous wild-type OR (95% CI): rs3110697: 0.6 (0.4-0.9), p-trend = 0.02; rs2132570: 0.2 (0.1-0.6), p-trend = 0.02). Three other IGFBP-3 SNPs (rs2854744, rs2960436 and rs2854746) were significantly associated with circulating IGFBP-3 levels (p < 0.01). Although these SNPs were not significantly associated with proliferative BBD risk, there was suggestive evidence that the alleles associated with higher circulating IGFBP-3 levels were also associated with higher risk of proliferative BBD. These results suggest that genetic variants and circulating levels of IGFBP-3 may play a role in the early stage of breast carcinogenesis.

IGF-I and IGFBP-3 polymorphisms in relation to circulating levels among African American and Caucasian women

Circulating insulin-like growth factor-I (IGF-I) and IGF-binding protein-3 (IGFBP-3) levels have been associated with common diseases. Although family-based studies suggest that genetic variation contributes to circulating IGF-I and IGFBP-3 levels, analyses of associations with multiple IGF-I and IGFBP-3 single nucleotide polymorphisms (SNP) have been limited, especially among African Americans. We evaluated 30 IGF-I and 15 IGFBP-3 SNPs and estimated diplotypes in association with plasma IGF-I and IGFBP-3 among 984 premenopausal African American and Caucasian women. In both races, IGFBP-3 rs2854746 (Ala32Gly) was positively associated with plasma IGFBP-3 (CC versus GG mean difference among Caucasians, 631 ng/mL; 95% confidence interval, 398-864; African Americans, 897 ng/mL; 95% confidence interval, 656-1,138), and IGFBP-3 diplotypes with the rs2854746 GG genotype had lower mean IGFBP-3 levels than reference diplotypes with the CG genotype, whereas IGFBP-3 diplotypes with the CC genotype had higher mean IGFBP-3 levels. IGFBP-3 rs2854744 (-202 A/C) was in strong linkage disequilibrium with rs2854746 in Caucasians only, but was associated with plasma IGFBP-3 in both races. Eight additional IGFBP-3 SNPs were associated with >or=5% differences in mean IGFBP-3 levels, with generally consistent associations between races. Twelve IGF-I SNPs were associated with >or=10% differences in mean IGF-I levels, but associations were generally discordant between races. Diplotype associations with plasma IGF-I did not parallel IGF-I SNP associations. Our study supports that common IGFBP-3 SNPs, especially rs2854746, influence plasma IGFBP-3 levels among African Americans and Caucasians but provides less evidence that IGF-I SNPs affect plasma IGF-I levels.

Genetic polymorphisms of the vitamin D binding protein and plasma concentrations of 25-hydroxyvitamin D in premenopausal women

BACKGROUND

Vitamin D status, determined on the basis of 25-hydroxyvitamin D [25(OH)D] concentrations, is associated with the risk of several diseases. Vitamin D binding protein (DBP) is the major carrier of vitamin D and its metabolites, but the role of DBP single nucleotide polymorphisms (SNPs) on 25(OH)D concentrations is unclear.

OBJECTIVE

The objective was to evaluate the association of 2 DBP gene SNPs with 25(OH)D concentrations and explore whether such association varies according to the amount of vitamin D that needs to be transported.

DESIGN

This cross-sectional study included 741 premenopausal white women, mostly of French descent. Plasma 25(OH)D concentrations were measured by radioimmunoassay. DBP-1 (rs7041) and DBP-2 (rs4588) were genotyped with a Sequenom MassArray platform. Associations and interactions were modeled by using multivariate linear regression.

RESULTS

DBP-1 and DBP-2 SNPs were in strong linkage disequilibrium and were both associated with 25(OH)D concentrations. An additional copy of the rare allele of DBP-1 or DBP-2 was associated with lower 25(OH)D concentrations (beta = -3.29, P for trend = 0.0003; beta = -4.22, P for trend < 0.0001, respectively). These DBP polymorphisms explained as much of the variation in circulating 25(OH)D as did total vitamin D intake (r2 = 1.3% for DBP-1, r2 = 2.0% for DBP-2, and r2 < or = 1.2% for vitamin D intake).

CONCLUSION

Circulating 25(OH)D concentrations in premenopausal women are strongly related to DBP polymorphisms. Whether DBP rare allele carriers have a different risk of vitamin D-related diseases and whether such carriers can benefit more or less from dietary interventions, vitamin D supplementation, or sun exposure need to be clarified.

Insulin receptor substrates (IRSs) and breast tumorigenesis

Insulin receptor substrate (IRS)-1 and IRS-2 are adaptor proteins in the insulin-like growth factor I (IGF-I)/IGF-I receptor (IGF-IR) pathway that mediate cell proliferation, migration, and survival. In addition to their role as scaffolding proteins in the cytoplasm, they are able to translocate into the nucleus and regulate gene transcription. IRS levels are developmentally and hormonally regulated in the normal mammary gland and both are essential for normal mammary gland bud formation and lactation. Both IRS-1 and IRS-2 are transforming oncogenes, and induce transformation and metastasis in vitro and in vivo. In breast cancer IRSs have unique functions, with IRS-1 being mainly involved in cell proliferation and survival, whereas IRS-2 has clear roles in cell migration and metastasis. In this review we will discuss the roles of IRSs in mammary gland development and breast cancer.

Effect of insulin-like growth factor gene polymorphisms alone or in interaction with diabetes on the risk of pancreatic cancer

Insulin-like growth factors (IGF) have been associated with risk of common human cancers, but the association between IGFs and pancreatic cancer risk is unclear. To determine whether genetic variations of IGF modify pancreatic cancer risk, we compared the frequency of six single nucleotide polymorphisms of IGF1 and IGF2 in a large-scale case control study. Single nucleotide polymorphisms were investigated using the TaqMan method in 892 patients with pancreatic ductal adenocarcinoma and 783 healthy controls who were recruited from The University of Texas M. D. Anderson Cancer Center from 2000 to 2007. Cases and controls were frequency matched by age (+/-5 years), race, and sex. Risk factor information was collected using direct interviews. We estimated odds ratios (OR) and 95% confidence intervals (95% CI) using unconditional multivariate logistic regression models. A haplotype of IGF1 gene containing the 3'-UTR Ex4 -177 G>C G allele had a significantly lower frequency in cases (0.027) than in controls (0.041; P = 0.039). A statistically significant joint effect of the IGF1 3'-UTR Ex4 -177 G>C C allele and diabetes on pancreatic cancer risk was observed. The OR (95% CI) were 1.07 (0.81-1.42), 2.12 (1.53-2.93), and 5.69 (2.63-12.3) for individuals who had the CC/CG genotype alone, diabetes alone, or both factors, respectively, compared with subjects without either of the two factors with adjustment for other risk factors. The IGF2 3'-UTR Ex4 -233C>T TT genotype was significantly associated with a reduced risk of pancreatic cancer (OR = 0.07; 95% CI = 0.01-0.57; P = 0.013). The polymorphic variants of the IGF genes may serve as a susceptibility factor for pancreatic cancer.

IGF binding proteins (IGFBPs) and regulation of breast cancer biology

The IGFBP family comprises six proteins with high affinity for the IGFs. Changes in the balance of the components of the IGF system may contribute to the progression of breast cancer. In tumours the abundance of IGFBPs relates to the estrogen receptor status and their production in the breast is controlled by hormones, principally estrogen and progesterone. Important interactions occur between IGFBPs and key growth regulators such as TGF-beta, PTEN and EGF which are reviewed. The conflicting observations between the effects of IGFBPs on the risk of breast cancer, in particular IGFBP-3, obtained from epidemiology studies in comparison to in vivo observations are highlighted and potential explanations provided. The functional activity of IGFBPs can also be affected by proteolysis, phosphorylation and glycosylation and the implications of these are described. The IGFs are generally present at levels far in excess of that required for maximal receptor stimulation, and the IGFBPs are critical regulators of their cellular actions. IGFBPs can affect cell function in an IGF-dependent or independent manner. The key mechanisms underlying the intrinsic actions of the IGFBPs are still in debate. IGF bioactivity locally in the breast is influenced not only by local tissue expression and regulation of IGFs, IGFBPs and IGFBP proteases, but also by these factors delivered from the circulation. Finally, the therapeutic potential of IGFBPs-2 and -3 are considered together with key questions that still need to be addressed.

Insulin and insulin-like growth factor signalling in neoplasia

Insulin and insulin-like growth factors (IGFs) are well known as key regulators of energy metabolism and growth. There is now considerable evidence that these hormones and the signal transduction networks they regulate have important roles in neoplasia. Epidermiological, clinical and laboratory research methods are being used to investigate novel cancer prevention and treatment strategies related to insulin and IGF signalling. Pharmacological strategies under study include the use of novel receptor-specific antibodies, receptor kinase inhibitors and AMP-activated protein kinase activators such as metformin. There is evidence that insulin and IGF signalling may also be relevant to dietary and lifestyle factors that influence cancer risk and cancer prognosis. Recent results are encouraging and have justified the expansion of many translational research programmes.

[Hormones and mammographic breast density]

Breast constitutional density may be altered and increased (acquired density) by hormonal interventions such as hormone replacement therapy (HRT). The effects of endogenous (steroids, prolactin, insulin-like factors...) and exogenous (HRT, levonorgestrel IUD, tibolone, tamoxifen, SERMs) hormones will be reviewed. Continuous combined estrogen-progestin preparations are most likely to cause an increase in density. Estrogen alone and tibolone are less likely to cause an increase in density. The sensitivity and specificity of mammography are decreased, with increased risk of interval carcinoma and rate of short interval follow-up from false positive results. The issue with regards to interruption of the hormonal therapy prior to mammography, and the duration of the interruption, are discussed.

Can genes for mammographic density inform cancer aetiology?

Mammographic density (MD) reflects variations in fat, stromal and epithelial tissues that are thought to be regulated by several genes. High MD is an established risk factor for breast cancer; therefore, genes that regulate MD may indirectly influence breast cancer. These genes might also be fewer in number and easier to identify than those for breast cancer risk outside of inherited predisposition syndromes. In this Perspective, we review the limited genetic studies of MD and propose future directions.

Association between IGF1 CA microsatellites and mammographic density, anthropometric measures, and circulating IGF-I levels in premenopausal Caucasian women

BACKGROUND

Results from several studies indicate that mammographic density, a strong risk factor for breast cancer, is greater in premenopausal women with higher circulating IGF-I levels. Both mammographic density and circulating IGF-I levels appear to be partly heritable traits. We hypothesized that in premenopausal women, IGF1 variants are associated with circulating IGF-I concentration, which in turn influences variation in breast density. Therefore, we examined the association of IGF1 polymorphisms with circulating IGF-I levels and mammographic density.

METHODS

Percentage density, amounts of dense and non-dense (fat) tissue, IGF-I levels, and BMI were measured in 163 premenopausal women. Three CA repeat polymorphisms were genotyped, one each at the 5' and 3' ends of IGF1 and one in intron 2.

RESULTS

The number of 19 alleles at the 5' polymorphism was associated with lower circulating levels of IGF-I (P = 0.02), whereas the number of 185 alleles at the 3' polymorphism was associated with higher percentage density (P = 0.03) and a smaller amount of non-dense tissue (P = 0.02). The strength of the effect of the 185 allele at 3' on percentage density was greatly reduced and statistical significance lost when BMI was included in regression models.

CONCLUSIONS

Our results suggest an association between the number of 185 alleles at 3' with percentage density. This association appears to be mediated by body composition and particularly body fat, as indicated by the association of 3' IGF1 genotype with non-dense (fat) tissue and the mediating effect of BMI on the association of 3' genotype with percentage density.