Radiol Oncol 2018; 52(2): 160-166. doi: 10.2478/raon-2018-0005 160 research article Matrix metalloproteinases polymorphisms as baseline risk predictors in malignant pleural mesothelioma Danijela Strbac¹, Katja Goricar², Vita Dolzan², Viljem Kovac¹ ¹ Institute of Oncology Ljubljana, Ljubljana, Slovenia ² Pharmacogenetics Laboratory, Institute of Biochemistry, Faculty of Medicine, University of Ljubljana, Ljubljana, Slovenia Radiol Oncol 2018; 52(2): 160-166. Received: 10 December 2017 Accepted: 17 December 2017 Correspondence to: Assist. Prof. Viljem Kovač, M.D., Ph.D., Institute of Oncology Ljubljana, Zaloška 2, SI-1000 Ljubljana, Slovenia. Phone: +386 1 5879 117; Fax: +386 1 5879 400; E-mail: vkovac@onko-i.si Disclosure: No potential conflicts of interest were disclosed Background. Malignant mesothelioma (MM) is a rare disease, linked to asbestos exposure in more than 80% of the cases. Matrix metalloproteinases (MMPs) have been identified as modulators of the tumour microenvironment and carcinogenesis. Polymorphisms of selected MMPs have been studied as potential biomarkers of time to progression (TTP) and overall survival (OS) in MM. The aim of our study was to investigate selected MMP polymorphisms as base- line risk predictors in MM development in combination with other well known risk factors, such as asbestos exposure. Patients and methods. The study included 236 patients and 161 healthy blood donors as the control group. Ten different polymorphisms in three MMP genes were genotyped using a fluorescence-based competitive allele-specific assay (KASPar): MMP2 rs243865, rs243849 and rs7201, MMP9 rs17576, rs17577, rs2250889 and rs20544, and MMP14 rs1042703, rs1042704 and rs743257. In statistical analyses continuous variables were described using median and range (25%–75%), while frequencies were used to describe categorical variables. Deviation from the Hardy-Weinberg equi- librium (HWE) was assessed using the standard chi-square test. The additive and dominant genetic models were used in statistical analyses. The association of genetic polymorphism with MM risk were examined by logistic regression to calculate odds ratios (ORs) and their 95% confidence intervals (CIs). Results. Carriers of at least one polymorphic MMP2 rs243865 allele tended to have a decreased risk for MM (OR = 0.66, 95% CI = 0.44–1.00; P = 0.050). The association was more pronounced in patients with known asbestos exposure: carriers of at least one polymorphic allele had significantly lower MM risk (OR = 0.55, 95% CI = 0.35–0.86; P = 0.009). None of the other tested polymorphisms showed association with the risk of malignant pleural mesothelioma. Conclusions. The MMP2 rs243865 polymorphism may have a protective role in malignant pleural mesothelioma development. This finding is even more evident in patients exposed to asbestos, implying a strong gene-environment interaction. Key words: matrix metalloproteinases; genetic polymorphism; malignant mesothelioma Introduction Malignant mesothelioma (MM) is a rare disease, linked to asbestos exposure in more than 80% of the cases. The latency period can last up to thir- ty years and estimated median survival is 9–12 months. The worldwide incidence of mesothe- lioma is slowly rising, with approximately 94 000 new cases per year. The most affected areas are parts of Europe, Australia and the USA.1 The rise in the MM incidence has been noticed in the Slovene population as well. The Slovenian nation- al registry follows the data on MM since 1961. The incidence in 2014 was 37 new cases per year in a population of approximately 2 million.2 Radiol Oncol 2018; 52(2): 160-166. Strbac D et al. / Matrix metalloproteinases and malignant mesothelioma 161 Several preclinical studies have identified ma- trix metalloproteinases (MMPs) as modulators of the tumour microenvironment and having an important role in carcinogenesis.3 MMPs are cal- cium-dependent, zinc-containing endopeptidases, with three common domains containing the pro- peptide, catalytic and haemopexin-like C-terminal domain.4 They are involved in tissue remodelling by interfering with the cell-cell and cell-extracel- lular matrix interactions. Studies have shown that MMPs, particularly MMP-2 and MMP-9, play a role in tumour angiogenesis, invasion and metas- tasis.5 The studies performed thus far show that MMPs and their inhibitory molecules, tissue in- hibitors of metalloproteinases (TIMPs), have an important role in proliferation and progression of MM and some other, more frequent malignancies, such as colon and breast cancer. Different MMP genes (MMP2, MMP9, MMP11, MMP14) and their expression were studied in mesothelioma tissue as potential prognostic markers.6 In a previous paper we studied the possible role of single nu- cleotide polymorphisms (SNPs) as potential mark- ers of treatment response.7 We identified MMP9 rs2250889, MMP9 rs20544, MMP14 rs1042703 as statistically significantly associated with overall survival (OS) in MM. Carriers of the polymorphic MMP9 rs2250889 and MMP14 rs1042703 alleles had shorter OS, compared to non-carriers, while carriers of polymorphic MMP9 rs20544 allele had longer OS.7 Many studies investigated the role of MMP poly- morphisms in the baseline genetic risk for common diseases and tumours, however, the role of MMP polymorphisms was found to be conflicting in dif- ferent diseases. In a large nested case-control study investigating skin cancer risk, MMP9 Arg668Gln polymorphism has been associated with a de- creased risk of squamous cell skin cancer (SCC).8 The opposite effect was observed in T-cell acute lymphoblastic leukaemia (T-ALL), where MMP2 rs243865 and MMP9 rs3918242 polymorphisms were associated with an increased risk of T-ALL.9 The data from the literature, linking MMP polymorphisms with tumour risk and the statisti- cally significant associations between the selected MMP2, MMP9 and MMP14 SNPs and time to pro- gression (TTP) and OS in MM, led us to further in- vestigate their potential role in baseline genetic risk of MM development. Our aim was to investigate selected MMP polymorphisms as baseline risk pre- dictors in MM development in combination with other well known risk factors, such as asbestos ex- posure. Patients and methods Patients Patients with histologically confirmed pleural or peritoneal mesothelioma diagnosed and treated between 2007 and 2016 were included in this retro- spective study. Patients were diagnosed mostly at the University Clinic Golnik and at the Department of Thoracic Surgery of the University Medical Centre Ljubljana. Patients were treated and fol- lowed-up at the Institute of Oncology Ljubljana, Slovenia. Most patients included in the study were also participating in previous studies on pharma- cogenomics of MM treatment, conducted at the Institute of Oncology Ljubljana, Slovenia. Some of the patients were also included in the clinical trial AGILI (Trial registration ID: NCT01281800).10 Clinical characteristics at diagnosis were ob- tained from medical records or assessed during clinical interview. Regarding asbestos exposure, patients were divided in two groups: patients with no known asbestos exposure and patients with known occupational or environmental exposure. The control group consisted of 161 unrelated healthy Slovenian blood donors, aged 49 to 65. The study was approved by the Slovenian National Medical Ethics Committee and was car- ried out according to the Declaration of Helsinki. DNA extraction and genotyping Genomic DNA was extracted from frozen whole- blood samples collected at the inclusion in any of the above mentioned studies using the Qiagen FlexiGene Kit (Qiagen, Hilden, Germany) in ac- cordance with the manufacturer’s instructions. Ten different polymorphisms in three MMP genes were genotyped: MMP2 rs243865, rs243849 and rs7201, MMP9 rs17576, rs17577, rs2250889 and rs20544, and MMP14 rs1042703, rs1042704 and rs743257. Predicted function of these poly- morphisms was assessed using SNP Function Prediction tools.11 The genotyping of all the SNPs was carried out using a fluorescence-based competitive allele-spe- cific assay (KASPar), according to the manufactur- er’s instructions (LGC Genomics, UK). For all investigated polymorphisms, 15% of samples were genotyped in duplicates. Genotyping quality control criteria included 100% duplicate call rate and 90% SNP-wise call rate. Radiol Oncol 2018; 52(2): 160-166. Strbac D et al. / Matrix metalloproteinases and malignant mesothelioma162 Statistical analyses Continuous and categorical variables were de- scribed using median and range (25%-75%) and frequencies, respectively. Deviation from the Hardy-Weinberg equilibrium (HWE) was assessed using the standard chi-square test. The additive and dominant genetic models were used in statisti- cal analyses. The associations of genetic polymor- phisms with MM risk were examined by logistic regression to calculate odds ratios (ORs) and their 95% confidence intervals (CIs). All statistical analyses were carried out by IBM SPSS Statistics, version 21.0 (IBM Corporation, Armonk, NY, USA). Haplotypes were reconstruct- ed and analysed using Thesias software, version 3.1. The most frequent haplotype was used as the reference. All statistical tests were two sided and the level of significance was set to P = 0.05. Due to the exploratory nature of the study, no adjust- ments for multiple comparisons were used. Results Patient characteristics In total, we included 236 patients with MM and 161 healthy blood donors as a control group. Clinical characteristics of patients are summarized in Table 1. Among controls, 125 (77.6%) were male and 36 (22.4%) were female. Median age was 55 (52–58.5) years. There were no significant differ- ences between cases and controls regarding gender (P = 0.375), however, controls were significantly younger than MM patients (P < 0.001). Genotyping analysis Variant allele frequencies for investigated SNPs are presented in Table 2. The distributions of all the investigated SNPs in the control group were in agreement with the Hardy-Weinberg equilibrium. Duplicate call rate was 100% for all SNPs. With the exception of one SNP that had a call rate of 92%, all SNPs had a call rate above 97%. Genotype frequencies for cases and controls are presented in Table 3. Carriers of at least one poly- morphic MMP2 rs243865 allele tended to have a de- creased risk for MM (OR = 0.66, 95% CI = 0.44-1.00; P = 0.050). The association was more pronounced in patients with known asbestos exposure: carriers of at least one polymorphic allele had significantly lower MM risk (OR = 0.55, 95% CI = 0.35–0.86; P = 0.009). As the number of homozygotes for poly- TABLE 1. Patients’ characteristics (N = 236) Characteristic N (%) Gender Male 174 (73.7) Female 62 (26.3) Age Median (25%-75%) 66 (58-72) Stage I 18 (7.6) II 60 (25.4) III 70 (29.7) IV 67 (28.4) Peritoneal 20 (8.5) Not determined 1 (0.4) Histological type Epitheloid 169 (71.6) Biphasic 27 (11.4) Sarcomatoid 26 (11.0) Not characterized 14 (5.9) ECOG performance status 0 15 (6.4) 1 114 (48.3) 2 92 (39.0) 3 15 (6.4) Metastases No 206 (87.3) Yes 30 (12.7) Asbestos exposure Not exposed 61 (26.5) [6] Exposed 169 (73.5) Smoking No 123 (57.7) Yes 106 (46.3) Numbers in square brackets denote the number of patients with missing data. ECOG = Eastern Cooperative Oncology Group TABLE 2. Variant allele characteristics, frequencies and agreement with HWE Gene SNP SNP characteristics Variant allele frequency PHWE MMP2 rs243865 c.-1306C>T 0.24 0.165 rs243849 c.999C>T, p.Asp333= 0.14 0.798 rs7201 c.*260A>C 0.41 0.441 MMP9 rs17576 c.836A>G, p.Gln279Arg 0.36 0.785 rs2250889 c.836A>G, p.Gln279Arg 0.05 0.535 rs17577 c.2003G>A, p.Arg668Gln 0.15 0.096 rs20544 c.*3C>T 0.44 0.445 MMP14 rs1042703 c.22T>C, p.Pro8Ser 0.26 0.164 rs1042704 c.817G>A, p.Asp273Asn 0.20 0.830 rs743257 c.*83C>T 0.50 0.519 HWE = Hardy-Weinberg equilibrium; SNP = single nucleotide polymorphism Radiol Oncol 2018; 52(2): 160-166. Strbac D et al. / Matrix metalloproteinases and malignant mesothelioma 163 TABLE 3. The association of investigated SNPs with risk for malignant mesothelioma SNP Genotype ControlsN (%) Cases N (%) OR (95% CI) P Cases exposed to asbestos N (%) OR (95% CI) P MMP2 rs243865 CC 90 (55.9) 155 (65.7) Ref. 118 (69.8) Ref. CT 65 (40.4) 77 (32.6) 0.69 (0.45-1.05) 0.081 48 (28.4) 0.56 (0.35-0.89) 0.015 TT 6 (3.7) 4 (1.7) 0.39 (0.11-1.41) 0.150 3 (1.8) 0.38 (0.09-1.57) 0.181 CT+TT 71 (44.1) 81 (34.3) 0.66 (0.44-1.00) 0.050 51 (30.2) 0.55 (0.35-0.86) 0.009 MMP2 rs243849 CC 108 (75.0) [17] 163 (71.5) [8] Ref. 116 (71.2) [6] Ref. CT 33 (22.9) 57 (25.0) 1.14 (0.70-1.87) 0.592 42 (25.8) 1.18 (0.70-2.00) 0.527 TT 3 (2.1) 8 (3.5) 1.77 (0.46-6.81) 0.408 5 (3.1) 1.55 (0.36-6.65) 0.554 CT+TT 36 (25.0) 65 (28.5) 1.20 (0.74-1.92) 0.459 47 (28.8) 1.22 (0.73-2.02) 0.451 MMP2 rs7201 AA 56 (35.9) [5] 78 (33.5) [3] Ref. 63 (37.5) [1] Ref. AC 71 (45.5) 114 (48.9) 1.15 (0.73-1.81) 0.539 78 (46.4) 0.98 (0.60-1.58) 0.923 CC 29 (18.6) 41 (17.6) 1.02 (0.56-1.82) 0.960 27 (16.1) 0.83 (0.44-1.56) 0.560 AC+CC 100 (64.1) 155 (66.5) 1.11 (0.73-1.70) 0.622 105 (62.5) 0.93 (0.59-1.47) 0.765 MMP9 rs17576 AA 64 (40.3) [2] 100 (42.9) [3] Ref. 74 (44.3) [2] Ref. AG 75 (47.2) 114 (48.9) 0.97 (0.63-1.49) 0.900 79 (47.3) 0.91 (0.57-1.44) 0.691 GG 20 (12.6) 19 (8.2) 0.61 (0.30-1.23) 0.165 14 (8.4) 0.61 (0.28-1.30) 0.196 AG+GG 95 (59.8) 133 (57.1) 0.90 (0.59-1.35) 0.599 93 (55.7) 0.85 (0.55-1.31) 0.458 MMP9 rs2250889 GG 146 (90.7) 212 (90.2) [1] Ref. 152 (89.9) Ref. GA 15 (9.3) 23 (9.8) 1.06 (0.53-2.09) 0.876 17 (10.1) 1.09 (0.52-2.26) 0.820 MMP9 rs17577 GG 113 (70.2) 169 (72.8) [4] Ref. 119 (71.3) [2] Ref. GA 47 (29.2) 60 (25.9) 0.85 (0.54-1.34) 0.490 45 (26.9) 0.91 (0.56-1.47) 0.699 AA 1 (0.6) 3 (1.3) 2.01 (0.21-19.53) 0.549 3 (1.8) 2.85 (0.29-27.79) 0.368 GA+AA 48 (29.8) 63 (27.2) 0.88 (0.56-1.37) 0.565 48 (28.7) 0.95 (0.59-1.53) 0.831 MMP9 rs20544 CC 33 (20.6) [1] 38 (16.3) [3] Ref. 29 (17.4) [2] Ref. CT 74 (46.3) 121 (51.9) 1.42 (0.82-2.46) 0.210 82 (49.1) 1.26 (0.70-2.27) 0.441 TT 53 (33.1) 74 (31.8) 1.21 (0.68-2.18) 0.518 56 (33.5) 1.20 (0.64-2.25) 0.563 CT+TT 127 (79.4) 195 (83.7) 1.33 (0.79-2.24) 0.275 138 (82.6) 1.24 (0.71-2.15) 0.453 MMP14 rs1042703 TT 90 (57.0) [3] 147 (63.4) [4] Ref. 109 (65.7) [3] Ref. TC 54 (34.2) 67 (28.9) 0.76 (0.49-1.18) 0.225 44 (26.5) 0.67 (0.41-1.09) 0.110 CC 14 (8.9) 18 (7.8) 0.79 (0.37-1.66) 0.530 13 (7.8) 0.77 (0.34-1.71) 0.518 TC+CC 68 (43.0) 85 (36.6) 0.77 (0.51-1.16) 0.204 57 (34.3) 0.69 (0.44-1.08) 0.108 MMP14 rs1042704 GG 103 (64.0) 160 (68.1) [1] Ref. 113 (66.9) Ref. GA 51 (31.7) 64 (27.2) 0.81 (0.52-1.26) 0.346 47 (27.8) 0.84 (0.52-1.35) 0.475 AA 7 (4.3) 11 (4.7) 1.01 (0.38-2.69) 0.982 9 (5.3) 1.17 (0.42-3.26) 0.761 GA+AA 58 (36.0) 75 (31.9) 0.83 (0.55-1.27) 0.395 56 (33.1) 0.88 (0.56-1.39) 0.581 MMP14 rs743257 CC 40 (26.0) [7] 59 (25.1) [1] Ref. 41 (24.4) [1] Ref. CT 73 (47.4) 104 (44.3) 0.97 (0.59-1.59) 0.892 76 (45.2) 1.02 (0.59-1.75) 0.955 TT 41 (26.6) 72 (30.6) 1.19 (0.68-2.07) 0.538 51 (30.4) 1.21 (0.67-2.21) 0.526 CT+TT 114 (74.0) 176 (74.9) 1.05 (0.66-1.67) 0.848 127 (75.6) 1.09 (0.66-1.80) 0.746 Numbers in square brackets denote the number of patients with missing data. Significant values are printed in bold. CI = confidence interval; OR = odds ratio; SNP = single nucleotide polymorphism Radiol Oncol 2018; 52(2): 160-166. Strbac D et al. / Matrix metalloproteinases and malignant mesothelioma164 morphic allele was low, we only observed a signifi- cant association with decreased MM risk for het- erozygotes in the additive model (Table 3). In haplotype analysis, no significant associa- tions with MM risk were observed, even when as- bestos exposure was taken into account (Table 4). Nevertheless, haplotypes that included the poly- morphic MMP2 rs243865 allele had slightly lower risk, consistent with single SNP analysis, but the association did not reach statistical significance. Discussion This study investigated the influence of MMP2, MMP9 and MMP14 gene polymorphisms on base- line risk for MM in comparison with healthy con- trol subjects. Carriers of MMP2 rs243865 CT or CT/ TT genotypes had significantly decreased risk for developing MM in comparison with CC homozy- gous genotype, especially in patients with known asbestos exposure. MMP2 rs243865 (c.-1306C>T) is a promoter polymorphism and our prior in silico analysis has shown that it may influence binding of transcrip- tion factors and may alter chromatin states.7 The data on whether the MMP2 rs243865 T allele has a protective function or if it contributes to higher risk for cancer, is somewhat conflicting for differ- ent malignancies. MMP polymorphisms have been extensively studied in many different common and rarer ma- lignancies.12,13 The most attractive and most sig- nificant MMPs in risk assessment studies were MMP2, MMP9 and MMP3 polymorphisms. MMP2 rs243865, that was associated with modified cancer risk in our study, had the greatest influence on can- cer risk in general. In accordance with our study, two meta-analysis presented the results showing that MMP2 rs243865 polymorphism had a protec- tive role in lung cancer susceptibility in both domi- nant and recessive models, which is consistent with our results. Seventeen studies were included in the meta-analysis and reported that the MMP2 rs2438651 polymorphism had a protective role on- ly in the Asian population.12,13 Considering that lung cancer is the most com- mon thoracic malignancy, these results can be par- allel to a less common thoracic malignancy such as MM. However, MMP polymorphisms in other common malignancies in the Asian population have been frequently studied. A meta-analysis of 12 publications studying urinary (renal and blad- der) cancers showed a lower risk for bladder can- cer with the T allele of MMP2 rs243865 in Asian patients but not in the Caucasian population.14 All of the above discussed publications present the MMP2 rs243865 T allele as having a somewhat protective role in cancer. There are publications that suggest the opposite effect of the T allele in MMP2 rs243865. A control based study that in- cluded a Caucasian population investigated six different polymorphisms in MMPs and TIMPs in bladder cancer patients. They concluded that the combined genotype carrying MMP2 rs243865 al- lele T with MMP9 rs3918242 allele T was found to increase bladder cancer risk.15 These results are the opposite to the previously mentioned Asian based metaanalysis.14 According to the db SNP and HapMap data on rs243865 frequency in genetically different popu- lations, the C allele is more common in Caucasian populations. That can perhaps contribute to the different results in different studied populations.16 Nevertheless, all of the cited studies find that MMP2 rs243865 could play a role as a risk factor in a variety of different malignancies. With regard to the MMP2 rs243865, T allele containing genotypes seem to have a protective role in predominantly thoracic malignancies, such as lung cancer and MM. Genome Wide Associated Study (GWAS) of 759 subjects in the Northern Italian population inves- tigated 15 different SNPs in several genes, and TABLE 4. The association of haplotypes with frequencies above 5% for investigated genes with risk for malignant mesotjelioma in patients with asbestos exposure Gene Haplotype Estimated frequency OR (95% CI) P MMP2 CCA 0.377 Ref. CCC 0.272 1.14 (0.77 - 1.68) 0.518 CTA 0.144 1.14 (0.70 - 1.85) 0.599 TCC 0.144 0.77 (0.48 - 1.25) 0.291 TCA 0.056 0.59 (0.26 - 1.38) 0.223 MMP9 ACGT 0.572 Ref. GCGC 0.204 0.86 (0.59 - 1.26) 0.440 GCAC 0.137 0.81 (0.52 - 1.26) 0.353 MMP14 TGC 0.338 Ref. TGT 0.267 1.39 (0.94 - 2.06) 0.103 CGT 0.125 0.85 (0.52 - 1.37) 0.494 TAT 0.110 1.23 (0.71 - 2.12) 0.461 CGC 0.080 1.33 (0.71 - 2.46) 0.371 The single nucleotide polymorphisms are ordered from the 5’- to 3’-end as follows: MMP2:rs243865, rs243849, rs7201; MMP9:rs17576, rs17577, rs2250889, rs20544; MMP14:rs1042703, rs1042704, rs743257. CI = confidence interval; OR = odds ratio Radiol Oncol 2018; 52(2): 160-166. Strbac D et al. / Matrix metalloproteinases and malignant mesothelioma 165 one of them was MMP14 rs2236304. Almost all of these SNPs had either a significant positive (higher risk after asbestos exposure) or negative (lower risk after asbestos exposure) interaction with as- bestos exposure, even after statistical corrections (Bonferroni) had been applied. But, the study has some limitations, such asthe small sample size, the age unbalanced control group and the possible ra- re genetics variants that could have been excluded from the GWAS statistical analysis.17 The MMP2 rs243865, T allele genotypes seem to have a protective role in predominantly tho- racic malignancies, such as lung cancer and MM. Moreover, thoracic malignancies are also well known to have a strong environmental component (eg. smoking, asbestos exposure).18 The gene-envi- ronment interactions have been studied extensive- ly in MM. The study that investigated the role of microsomal epoxide hydrolase (mEH), glutathione S-transferases (GSTM1, GSTT1), N-acetytransferase 2 (NAT2), and cytochrome P1A1 (CYP1A1) geno- types concluded that the presence of synergisms between genotypes, i.e., mEH and NAT2, mEH and GSTM, and NAT2 and GSTM1 combined with the interaction observed with exposure to asbes- tos, suggests the presence of gene-environment and gene–gene interactions in the development of MM.19 Our results suggest a combined effect of asbestos exposure and MMP2 rs243865. Gene-environment interactions in asbestos related diseases have been previously studied in enzymes such as catalase (CAT), superoxide dismutase (SOD 2, SOD3) and inducible nitric oxide synthase (iNOS), which are part of the enzymatic defence system against re- active oxygen species (ROS). Besides gene-gene interactions between MnSOD Ala -9Val and CAT -262 C>T polymorphisms as well as iNOS and CAT -262 C>T polymorphisms and the risk of asbestosis, gene-environment interactions were also reported. A strong interaction was reported between GSTM1- null polymorphism and smoking, iNOS (CCTTT)n polymorphism and smoking, and between iNOS (CCTTT)n polymorphism and cumulative asbes- tos exposure, suggesting that interactions between different genotypes, genotypes and smoking, and between genotypes and asbestos exposure have an important influence on the development of as- bestosis.20 These studies on asbestosis suggest, that gene-environment interactions should be inves- tigated also in other asbestos related diseases, in- cluding MM, since asbestos exposure is a proven environmental risk factor in MM. Despite some limitations of our study, such as a small sample size and a control group that was not appropriately age balanced, low rate of patient as- bestos exposure and lacking this data of the control group, our results reached statistical significance and showed that there could be a genetic predis- position of certain MMP SNPs for MM and that there is a potential gene-environment interaction between MMP SNPs and asbestos that is a major risk factor for MM. In conclusion, our data suggests that MMP2 rs243865 polymorphism may have a protective role in malignant pleural mesothelioma. This find- ing is even more pronounced in patients exposed to asbestos, implying a strong gene-environment interaction. Acknowledgments Barbara Možina MSc, the head of the Biochemical Laboratory at the Institute of Oncology Ljubljana, provided valuable help in blood sample collection and storage as well as logistical help in managing the blood samples. References 1. 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