APOBEC3A/B deletion polymorphism and endometrial cancer risk.

BACKGROUND: A common 30 kb deletion affecting the APOBEC3A and APOBEC3B genes has been linked to increased APOBEC activity and APOBEC-related mutational signatures in human cancers. The role of this deletion as a cancer risk factor remains controversial. MATERIALS AND METHODS: We genotyped the APOBEC3A/B deletion in a sample of 1,470 Norwegian endometrial cancer cases and compared to 1,918 healthy controls. For assessment across Caucasian populations, we mined genotypes of the SNP rs12628403, which is in strong linkage disequilibrium with the deletion, in a GWAS dataset of 4,274 cases and 18,125 healthy controls, through the ECAC consortium. RESULTS: We found the APOBEC3A/B deletion variant to be significantly associated with reduced risk of endometrial cancer among Norwegian women (OR = 0.75; 95% CI = 0.62-0.91; p = 0.003; dominant model). Similar results were found in the subgroup of endometrioid endometrial cancer (OR = 0.64; 95% CI = 0.51-0.79; p = 3.6 × 10-5 ; dominant model). The observed risk reduction was particularly strong among individuals in the range of 50-60 years of age (OR = 0.51; 95% CI = 0.33-0.78; p = 0.002; dominant model). In the different populations included in the ECAC dataset, the ORs varied from 0.85 to 1.05. Although five out of six populations revealed ORs <1.0, the overall estimate was nonsignificant and, as such, did not formally validate the findings in the Norwegian cohort. CONCLUSION: The APOBEC3A/B deletion polymorphism is associated with a decreased risk of endometrial cancer in the Norwegian population.

Impact of the APOBEC3A/B deletion polymorphism on risk of ovarian cancer.

A germline 29.5-kb deletion variant removes the 3' end of the APOBEC3A gene and a large part of APOBEC3B, creating a hybrid gene that has been linked to increased APOBEC3 activity and DNA damage in human cancers. We genotyped the APOBEC3A/B deletion in hospital-based samples of 1398 Norwegian epithelial ovarian cancer patients without detected BRCA1/2 germline mutations and compared to 1,918 healthy female controls, to assess the potential cancer risk associated with the deletion. We observed an association between APOBEC3A/B status and reduced risk for ovarian cancer (OR = 0.75; CI = 0.61-0.91; p = 0.003) applying the dominant model. Similar results were found in other models. The association was observed both in non-serous and serous cases (dominant model: OR = 0.69; CI = 0.50-0.95; p = 0.018 and OR = 0.77; CI = 0.62-0.96; p = 0.019, respectively) as well as within high-grade serous cases (dominant model: OR = 0.79; CI = 0.59-1.05). For validation purposes, we mined an available large multinational GWAS-based data set of > 18,000 cases and > 26,000 controls for SNP rs12628403, known to be in linkage disequilibrium with the APOBEC3A/B deletion. We found a non-significant trend for SNP rs12628403 being linked to reduced risk of ovarian cancer in general and similar trends for all subtypes. For clear cell cancers, the risk reduction reached significance (OR = 0.85; CI = 0.69-1.00).

Polymorphisms in the TP53-MDM2-MDM4-axis in patients with rheumatoid arthritis.

BACKGROUND: In addition to being a tumour suppressor, TP53 is a suppressor of inflammation, and dysfunction of this gene has been related to autoimmune diseases. Patients with autoimmunity, such as rheumatoid arthritis (RA) have an increased risk of certain cancers, like lymphomas, indicating that some underlying mechanisms may modulate risk of both cancers and autoimmunity. METHODS: We genotyped 5 common genetic variants in TP53 and its main regulators MDM2 and MDM4 in a sample of 942 RA patients and 3,747 healthy controls, and mined previously published GWAS-data, to assess the potential impact of these variants on risk of RA. RESULTS: For the TP53 Arg72Pro polymorphism (rs1042522), MDM4 SNP34091 (rs4245739) and MDM2 SNP285C (rs117039649), we found no association to risk of RA. For MDM2 SNP309 (rs2279744), the minor G-allele was associated with a reduced risk of RA (OR: 0.87; CI: 0.79-0.97). This association was also seen in genotype models (OR: 0.86; CI: 0.74-0.99 and OR: 0.79; CI 0.63-0.99; dominant and recessive model, respectively), but was not validated in a large GWAS data set. For MDM2 del1518 (rs3730485), the minor del-allele was associated with an increased risk of RA in the dominant model (OR: 1.18; CI: 1.02-1.38). Stratifying RA cases and controls into phylogenetic subgroups according to the combined genotypes of all three MDM2 polymorphism, we found individuals with the del158-285-309 genotype del/ins-G/G-T/T to have an increased risk of RA as compared to those with the ins/ins-G/G-G/G genotype (OR: 1.56; CI: 1.18-2.06) indicating opposite effects of the del1518 del-allele and the SNP309 G-allele. CONCLUSION: We find a potential association between the MDM2 del1518 variant and RA, and indications that combinatorial genotypes and haplotypes in the MDM2 locus may be related to RA.

Impact of MDM2 promoter SNP55 (rs2870820) on risk of endometrial and ovarian cancer.

BACKGROUND: While large GWAS analyses have not found convincing associations between MDM2 promoter SNP55 and gynaecological cancers, SNP55 is in linkage disequilibrium with two other functional SNPs in the same promoter, likely to obscure associations between single SNPs and cancer risk. Here, we assessed the impact of SNP55 on risk of endometrial and ovarian cancer, including sub-analyses stratified for other functional SNPs in the region. MATERIAL AND METHODS: Using a custom LightSNiP assay, we genotyped SNP55 in two large hospital-based cohorts of patients with ovarian (n = 1,332) and endometrial (n = 1,363) cancer and compared genotypes to healthy female controls (n = 1,858). RESULTS: Among individuals harbouring the SNP309TT genotype, the minor SNP55T-allele was associated with a reduced risk of endometrial (dominant model: OR = 0.63; CI = 0.45-0.88; p = 0.01). Regardless of the genotype in neighbouring SNPs, the SNP55T-allele was also associated with a reduced risk of endometrial cancer before 50 years of age (dominant model: OR = 0.56; CI = 0.34-0.90; p = 0.02). No association between SNP55 status and ovarian cancer risk was observed. CONCLUSIONS: MDM2 SNP55T-allele may correlate with reduced risk for endometrial cancer in a SNP309T-, but not SNP309G, context.

APOBEC3A/B deletion polymorphism and cancer risk.

Activity of the apolipoprotein B mRNA editing enzyme, catalytic-polypeptide-like (APOBEC) enzymes has been linked to specific mutational processes in human cancer genomes. A germline APOBEC3A/B deletion polymorphism is associated with APOBEC-dependent mutational signatures, and the deletion allele has been reported to confer an elevated risk of some cancers in Asian populations, while the results in European populations, so far, have been conflicting. We genotyped the APOBEC3A/B deletion polymorphism in a large population-based sample consisting of 11 106 Caucasian (Norwegian) individuals, including 7279 incident cancer cases (1769 breast, 1360 lung, 1585 colon, and 2565 prostate cancer) and a control group of 3827 matched individuals without cancer (1918 females and 1909 males) from the same population. Overall, the APOBEC3A/B deletion polymorphism was not associated with risk of any of the four cancer types. However, in subgroup analyses stratified by age, we found that the deletion allele was associated with increased risk for lung cancer among individuals <50 years of age (OR 2.17, CI 1.19-3.97), and that the association was gradually reduced with increasing age (P = 0.01). A similar but weaker pattern was observed for prostate cancer. In support of these findings, the APOBEC3A/B deletion was associated with young age at diagnosis among the cancer cases for both cancer forms (lung cancer: P = 0.02; dominant model and prostate cancer: P = 0.03; recessive model). No such associations were observed for breast or colon cancer.

The Functional Roles of the MDM2 Splice Variants P2-MDM2-10 and MDM2-∆5 in Breast Cancer Cells.

BACKGROUND: MDM2 is a negative regulator of p53 and is upregulated in numerous human cancers. While different MDM2 splice variants have been observed in both normal tissues and malignant cells, their functions are poorly understood. METHODS: We evaluated the effect of MDM2 splice variants by overexpression in MCF-7 cells and analyses of expression of downstream genes (qPCR and Western blot), subcellular localization (immunofluorescence), cell cycle assays (Nucleocounter3000), apoptosis analysis (Annexin V detection), and induction of senescence (ß-galactosidase analysis). RESULTS: In a screen for MDM2 splice variants in MCF-7 breast cancer cells, extended with data from healthy leukocytes, we found P2-MDM2-10 and MDM2-Δ5 to be the splice variants expressed at highest levels. Contrasting MDM2 full-length protein, we found normal tissue expression levels of P2-MDM2-10 and MDM2-Δ5 to be highest in individuals harboring the promoter SNP309TT genotype. While we detected no protein product coded for by MDM2-Δ5, the P2-MDM2-10 variant generated a protein markedly more stable than MDM2-FL. Both splice variants were significantly upregulated in stressed cells (P=4.3 × 10-4 and P=7.1 × 10-4, respectively). Notably, chemotherapy treatment and overexpression of P2-MDM2-10 or MDM2-Δ5 both lead to increased mRNA levels of the endogenous MDM2-FL (P=.039 and P=.070, respectively) but also the proapoptotic gene PUMA (P=.010 and P=.033, respectively), accompanied by induction of apoptosis and repression of senescence. CONCLUSION: We found P2-MDM2-10 and MDM2-Δ5 to have distinct biological functions in breast cancer cells. GENERAL SIGNIFICANCE: Alternative splicing may influence the oncogenic effects of the MDM2 gene.

Impact of the MDM2 splice-variants MDM2-A, MDM2-B and MDM2-C on cytotoxic stress response in breast cancer cells.

BACKGROUND: The murine double minute 2 (MDM2) is an oncogene and a negative regulator of the tumor suppressor protein p53. MDM2 is known to be amplified in numerous human cancers, and upregulation of MDM2 is considered to be an alternative mechanism of p53 inactivation. The presence of many splice variants of MDM2 has been observed in both normal tissues and malignant cells; however their impact and functional properties in response to chemotherapy treatment are not fully understood. Here, we investigate the biological effects of three widely expressed alternatively spliced variants of MDM2; MDM2-A, MDM2-B and MDM2-C, both in unstressed MCF-7 breast cancer cells and in cells subjected to chemotherapy. We assessed protein stability, subcellular localization and induction of downstream genes known to be regulated by the MDM2-network, as well as impact on cellular endpoints, such as apoptosis, cell cycle arrest and senescence. RESULTS: We found both the splice variants MDM2-B and -C, to have a much longer half-life than MDM2 full-length (FL) protein after chemotherapy treatment indicating that, under stressed conditions, the regulation of degradation of these two variants differs from that of MDM2-FL. Interestingly, we observed all three splice variants to deviate from MDM2-FL protein with respect to subcellular distribution. Furthermore, while MDM2-A and -B induced the expression of the pro-apoptotic gene PUMA, this effect did not manifest in an increased level of apoptosis. CONCLUSION: Although MDM2-B induced slight changes in the cell cycle profile, overall, we found the impact of the three MDM2 splice variants on potential cellular endpoints upon doxorubicin treatment to be limited.

MDM2 promoter polymorphism del1518 (rs3730485) and its impact on endometrial and ovarian cancer risk.

BACKGROUND: The del1518 (rs3730485) polymorphism is an in/del variant in the MDM2 promoter P1. The variant is in complete linkage disequilibrium with MDM2 SNP309 (rs2279744) and has previously been found associated with an increased risk of colon cancer. In this study we assessed the impact of MDM2 del1518 on risk of ovarian and endometrial cancer. METHODS: Here, we genotyped del1518 in two large hospital-based series of patients diagnosed with ovarian (n = 1,385) or endometrial (n = 1,404) cancer and performed risk estimations as compared to the genotype distribution among 1,872 healthy female controls. RESULTS: In overall analysis we observed no association between del1518 and risk of either ovarian or endometrial cancer. However, stratifying according to SNP309 status, we found the del1518 variant to be associated with a reduced risk of endometrial cancer among individuals carrying the SNP309TT genotype both in the dominant (OR = 0.64; 95% CI = 0.45 - 0.90) and the recessive model (OR = 0.80; 95% CI = 0.65 - 1.00). No such association was observed for ovarian cancer risk. CONCLUSION: We found the MDM2 del1518 del variant to be associated with reduced risk of endometrial cancer among individuals carrying the MDM2 SNP309TT genotype.

Detection of mutant KRAS and TP53 DNA in circulating exosomes from healthy individuals and patients with pancreatic cancer.

Pancreatic cancer presents with a dismal mortality rate and is in urgent need of methods for early detection with potential for timely intervention. All living cells, including cancer cells, generate exosomes. We previously discovered double stranded genomic DNA in exosomes derived from the circulation of pancreatic cancer patients, which enabled the detection of prevalent mutations associated with the disease. Here, we report a proof-of-concept study that demonstrates the potential clinical utility of circulating exosomal DNA for identification of KRASG12D and TP53R273H mutations in patients with pancreas-associated pathologies, including pancreatic ductal adenocarcinoma (PDAC), chronic pancreatitis (CP) and intraductal papillary mucinous neoplasm (IPMN), and in healthy human subjects. In 48 clinically annotated serum samples from PDAC patients, digital PCR analyses of exosomal DNA identified KRASG12D mutation in 39.6% of cases, and TP53R273H mutation in 4.2% of cases. KRASG12D and TP53R273H mutations were also detected in exosomal DNA from IPMN patients (2 out of 7 with KRASG12D, one of which also co-presented with TP53R273H mutation). Circulating exosomal DNA in 5 out of 9 CP patients enabled the detection of KRASG12D mutation. In 114 healthy subject-derived circulating exosomal DNA, 2.6% presented with KRASG12D mutation and none with TP53R273H mutation. This study highlights the value of circulating exosomal DNA for a rapid, low-cost identification of cancer driving mutations. The identification of mutations in IPMN patients and healthy subjects suggests that liquid biopsies may allow potential assessment of cancer risk but with a cautionary note that detection of clinical cancer cannot be assumed.

Prevalence of the CHEK2 R95* germline mutation.

BACKGROUND: While germline CHEK2 mutations have been linked to a moderately elevated cancer risk, to date, a limited number of such mutations have been identified. Recently, we reported a germline nonsense mutation (C283T; R95*), introducing an early stop-codon, in two Norwegian patients diagnosed with locally advanced breast cancer. Both patients were resistant to anthracycline therapy, resembling what has been observed for TP53 mutations. METHODS: In the present study, we screened a large population based sample, including 3748 non-cancer individuals and 7081 incident cancer cases (breast cancer, n = 1717; prostate cancer n = 2501, lung cancer n = 1331 and colorectal cancer n = 1532), for the distribution of CHEK2 R95*. RESULTS: We found that 12 individuals (0.11 %) carried the R95* variant: 4 non-cancer individuals (0.11 %), 4 breast cancer cases (0.23 %), and 4 prostate cancer cases (0.16 %). Although the low number of observations precluded formal statistical assessment, our data may indicate an elevated risk for breast (OR: 2.19, 95 % CI: 0.55-8.75) and prostate cancer (OR: 1.5, 95 % CI: 0.36-6.00) associated with CHEK2 R95*. By mining international databanks, we found no individuals carrying the R95* mutation, indicating it to be restricted to the Norwegian population. CONCLUSION: We provide proof-of-concept that previously unknown CHEK2 germline mutations may be present in certain populations. Notably, germline mutations in tumours are in general missed by contemporary massive parallel sequencing strategies, since tumour mutations are usually filtered against the germline. The fact that the CHEK2 R95* mutation may be associated with resistance to anthracyclines in cancer patients emphasizes its possible clinical importance.

MDM2 promoter SNP55 (rs2870820) affects risk of colon cancer but not breast-, lung-, or prostate cancer.

Two functional SNPs (SNP285G > C; rs117039649 and SNP309T > G; rs2279744) have previously been reported to modulate Sp1 transcription factor binding to the promoter of the proto-oncogene MDM2, and to influence cancer risk. Recently, a third SNP (SNP55C > T; rs2870820) was also reported to affect Sp1 binding and MDM2 transcription. In this large population based case-control study, we genotyped MDM2 SNP55 in 10,779 Caucasian individuals, previously genotyped for SNP309 and SNP285, including cases of colon (n = 1,524), lung (n = 1,323), breast (n = 1,709) and prostate cancer (n = 2,488) and 3,735 non-cancer controls, as well as 299 healthy African-Americans. Applying the dominant model, we found an elevated risk of colon cancer among individuals harbouring SNP55TT/CT genotypes compared to the SNP55CC genotype (OR = 1.15; 95% CI = 1.01-1.30). The risk was found to be highest for left-sided colon cancer (OR = 1.21; 95% CI = 1.00-1.45) and among females (OR = 1.32; 95% CI = 1.01-1.74). Assessing combined genotypes, we found the highest risk of colon cancer among individuals harbouring the SNP55TT or CT together with the SNP309TG genotype (OR = 1.21; 95% CI = 1.00-1.46). Supporting the conclusions from the risk estimates, we found colon cancer cases carrying the SNP55TT/CT genotypes to be diagnosed at younger age as compared to SNP55CC (p = 0.053), in particular among patients carrying the SNP309TG/TT genotypes (p = 0.009).

Associations between the MDM2 promoter P1 polymorphism del1518 (rs3730485) and incidence of cancer of the breast, lung, colon and prostate.

The MDM2 promoter region contains several polymorphisms, some of which have been associated with MDM2 expression, cancer risk and age at cancer onset. del1518 (rs3730485) is an indel polymorphism residing in the MDM2 promoter P1 and is in almost complete linkage disequilibrium with the MDM2 promoter P2 polymorphism SNP309T>G (rs2279744). Cancer risk assessments of del1518 have previously been conducted in relatively small Chinese populations only. In this study we assessed the genotype distribution of del1518 among healthy Caucasians, African Americans and Chinese, and we estimated the Odds Ratios (OR) for incident cancer of the breast, colon, lung and prostate (n=7,081) as compared to controls (n=3,749) in a large Caucasian (Norwegian) cohort.We found the genotypes of the del1518 to vary significantly between healthy Caucasians, African-Americans and Chinese (p< 1×10-5). Further, we found a positive association of the del1518 del-allele with risk of colon cancer (dominant model: OR = 1.15; 95 % CI = 1.01 - 1.31). Stratifying according to SNP309 status, this association remained among carriers of the SNP309TG genotype (OR = 1.21; 95 % CI = 1.01 - 1.46), but with no clear association among carriers of the SNP309TT genotype. In conclusion, our findings suggest del1518 to be associated with increased risk of colon cancer.

The MDM4 SNP34091 (rs4245739) C-allele is associated with increased risk of ovarian-but not endometrial cancer.

The MDM4 protein (also known as MDMX or HDMX) is a negative regulator of p53, not only by direct interaction but also through its interaction with MDM2. Further, MDM4 overexpression and amplification have been observed in several cancer forms. Recently, a single nucleotide polymorphism (SNP) in the 3' untranslated region of the MDM4 gene, SNP34091A > C (rs4245739) was reported to alter MDM4 messenger RNA (mRNA) stability by modulating a microRNA binding site, thereby leading to decreased MDM4 levels. In this case-control study, we aimed to evaluate the possible association between MDM4 SNP34091 status and cancer risk by comparing the genotype frequencies in large hospital-based cohorts of endometrial- (n = 1404) and ovarian (n = 1385) cancer patients with healthy female controls (n = 1870). Genotype frequencies were compared by odds ratio (OR) estimates and Fisher exact tests. We found that individuals harboring the MDM4 SNP34091AC/CC genotypes had a significantly elevated risk for serous ovarian cancer (SOC) in general and high-grade serous ovarian cancer (HGSOC) in particular (SOC: OR = 1.18., 95 % CI = 1.01-1.39; HGSOC: OR = 1.25, CI = 1.02-1.53). No association between SNP34091 genotypes and endometrial cancer risk was observed. Our data indicate the MDM4 SNP34091AC/CC genotypes to be associated with an elevated risk for SOC and in particular the HGSOC type.

MDM4 SNP34091 (rs4245739) and its effect on breast-, colon-, lung-, and prostate cancer risk.

The MDM4 protein plays an important part in the negative regulation of the tumor suppressor p53 through its interaction with MDM2. In line with this, MDM4 amplification has been observed in several tumor forms. A polymorphism (rs4245739 A>C; SNP34091) in the MDM4 3' untranslated region has been reported to create a target site for hsa-miR-191, resulting in decreased MDM4 mRNA levels. In this population-based case-control study, we examined the potential association between MDM4 SNP34091, alone and in combination with the MDM2 SNP309T>G (rs2279744), and the risk of breast-, colon-, lung-, and prostate cancer in Norway. SNP34091 was genotyped in 7,079 cancer patients as well as in 3,747 gender- and age-matched healthy controls. MDM4 SNP34091C was not associated with risk for any of the tumor forms examined, except for a marginally significant association with reduced risk for breast cancer in a recessive model (OR = 0.77: 95% CI = 0.59-0.99). Stratifying according to MDM2 SNP309 status, we observed a reduced risk for breast cancer related to MDM4 SNP34091CC among individuals harboring the MDM2 SNP309GG genotype (OR = 0.41; 95% CI = 0.21-0.82). We conclude, MDM4 SNP34091 status to be associated with reduced risk of breast cancer, in particular in individuals carrying the MDM2 SNP309GG genotype, but not to be associated with either lung-, colon- or prostate cancer.

Influence of MDM2 SNP309 and SNP285 status on the risk of cancer in the breast, prostate, lung and colon.

MDM2 is a key regulator of the p53 tumor suppressor protein and is overexpressed in many human cancers. Two single nucleotide polymorphisms (SNPs) located in the MDM2 intronic promoter (P2) have been found to exert biological function. The G-allele of SNP309T>G; rs2279744 increases MDM2 transcription and has been linked to increased cancer risk. In contrast, the less frequent SNP285G>C; rs117039649, which is in complete linkage disequilibrium with SNP309 (generating a SNP285C/309G variant haplotype), has been related to reduced MDM2 transcription and to reduced risk of breast, endometrial and ovarian cancer. In this large population-based case-control study, we genotyped SNP309 and SNP285 in 10,830 individuals, including cases with cancer of the breast (n=1,717), colon (n=1,532), lung (n=1,331) and prostate (n=2,501), as well as 3,749 non-cancer controls. We found a slightly reduced risk for lung cancer among individuals harboring the SNP309TG/GG genotypes compared to the SNP309TT genotype (OR= 0.86; CI = 0.67-0.98), but this association was restricted to women (OR = 0.77; CI = 0.63-0.95) and was not present among men (OR = 0.91; CI = 0.77-1.08). Consistent with previous findings, we found a reduced risk for breast cancer among individuals carrying the SNP285GC/309GG genotype versus the SNP285GG/309GG genotype (OR = 0.55; CI = 0.33-0.93). In conclusion, our data support the hypothesis that the effects of both SNP285 and SNP309 status are tissue dependent.

Population distribution and ancestry of the cancer protective MDM2 SNP285 (rs117039649).

The MDM2 promoter SNP285C is located on the SNP309G allele. While SNP309G enhances Sp1 transcription factor binding and MDM2 transcription, SNP285C antagonizes Sp1 binding and reduces the risk of breast-, ovary- and endometrial cancer. Assessing SNP285 and 309 genotypes across 25 different ethnic populations (>10.000 individuals), the incidence of SNP285C was 6-8% across European populations except for Finns (1.2%) and Saami (0.3%). The incidence decreased towards the Middle-East and Eastern Russia, and SNP285C was absent among Han Chinese, Mongolians and African Americans. Interhaplotype variation analyses estimated SNP285C to have originated about 14,700 years ago (95% CI: 8,300 - 33,300). Both this estimate and the geographical distribution suggest SNP285C to have arisen after the separation between Caucasians and modern day East Asians (17,000 - 40,000 years ago). We observed a strong inverse correlation (r = -0.805; p < 0.001) between the percentage of SNP309G alleles harboring SNP285C and the MAF for SNP309G itself across different populations suggesting selection and environmental adaptation with respect to MDM2 expression in recent human evolution. In conclusion, we found SNP285C to be a pan-Caucasian variant. Ethnic variation regarding distribution of SNP285C needs to be taken into account when assessing the impact of MDM2 SNPs on cancer risk.

MDM2 promoter SNP344T>A (rs1196333) status does not affect cancer risk.

The MDM2 proto-oncogene plays a key role in central cellular processes like growth control and apoptosis, and the gene locus is frequently amplified in sarcomas. Two polymorphisms located in the MDM2 promoter P2 have been shown to affect cancer risk. One of these polymorphisms (SNP309T>G; rs2279744) facilitates Sp1 transcription factor binding to the promoter and is associated with increased cancer risk. In contrast, SNP285G>C (rs117039649), located 24 bp upstream of rs2279744, and in complete linkage disequilibrium with the SNP309G allele, reduces Sp1 recruitment and lowers cancer risk. Thus, fine tuning of MDM2 expression has proven to be of significant importance with respect to tumorigenesis. We assessed the potential functional effects of a third MDM2 promoter P2 polymorphism (SNP344T>A; rs1196333) located on the SNP309T allele. While in silico analyses indicated SNP344A to modulate TFAP2A, SPIB and AP1 transcription factor binding, we found no effect of SNP344 status on MDM2 expression levels. Assessing the frequency of SNP344A in healthy Caucasians (n = 2,954) and patients suffering from ovarian (n = 1,927), breast (n = 1,271), endometrial (n = 895) or prostatic cancer (n = 641), we detected no significant difference in the distribution of this polymorphism between any of these cancer forms and healthy controls (6.1% in healthy controls, and 4.9%, 5.0%, 5.4% and 7.2% in the cancer groups, respectively). In conclusion, our findings provide no evidence indicating that SNP344A may affect MDM2 transcription or cancer risk.