Association between Four MMP-9 Polymorphisms and Breast Cancer Risk: A Meta-Analysis

Background

Breast cancer, a global health concern, is the most common cancer worldwide, and ranks as the fifth leading cause of cancer-related death [1]. It represents 22.9% of total female cancers [2]. Approximately 232 670 new cases and 40 000 death are expected to occur in 2014 among women in the United States [3]. The incidence rates in more developed countries and less developed countries were 71.7 and 29.3 per 100 000 persons per year, respectively, and the corresponding mortality rates were 17.1 and 11.8, with 5-year relative survival rate ranging from 12% to 90% [4]. The introduction of population-based screening using mammography and the systemic use of adjuvant therapies contribute to observed improvements in breast cancer survival. A meta-analysis showed that identification of risk factors for breast cancer might be useful for personalized mammography screening [5]. Thus, it is important to discuss the risk factors, explore the mechanism underlying this disease, and identify the best diagnostic marker to diagnose early-stage breast carcinogenesis.

In recent decades, gene mutations were shown to be risk factors for breast cancer occurrence [6] and an independent prognostic marker for patients who received adjuvant therapy [7]. Matrix metalloproteinase (MMPs) are a multifunctional family of endopeptidases participating in the degradation of extracellular matrix and basement membrane barriers [8] and also play key roles in separating the tumor cells from normal surrounding tissues [9,10]. MMP-9, also known as 92-kD type IV collagenase or gelatinase B, is a member of the MMPs family and is a zinc-dependent peptidase. It regulates inflammation in cancer tissues and diseases [11]. Differential expression in breast cancer cells of MMP-9 affects the degree of cellular differentiation and is closely correlated with the most aggressive subtypes [12]. Genetic variation may influence MMP-9 expression, resulting in development of cancer susceptibility. The human MMP-9 gene is located on chromosome region 20q11.2–q13.1 [13]. Several single-nucleotide polymorphisms (SNPs) have been reported to be associated with tumor progression. MMP-9-1562 C/T polymorphism (rs3918242), a C to T substitution at −1562bp, was the most studied and is associated with increased risk of deep vein thrombosis [14] and colorectal cancer [15] in cancer patients. MMP-9 P574R (rs2250889, a C to G substitution in exon 10) and R279Q (rs17576, a G to A substitution in exon 6) functional polymorphisms are biomarkers for the occurrence and metastasis of primary lung cancer [16]. MMP-9 rs3787268, a G to A substitution, was shown to have strongest association with breast cancer among the Native American women [17].

Although research has been performed to explore the effect of MMP-9 polymorphisms in breast cancer susceptibility, results are inconclusive. Grieu et al. found that patients with MMP-9–1562 CT or TT genotypes showed marginally better prognosis compared to CC homozygotes [18] but Roehe et al. found no significant association between MMP-9–1562C/T polymorphism and breast cancer risk [19]. Furthermore, the breast cancer incidence rates vary by country. Therefore, we conducted this meta-analysis to investigate the relationship between MMP-9 polymorphisms and breast cancer risk.

Material and Methods

SEARCH STRATEGY:

We conducted a literature search using the online electronic databases of EBSCO (PubMed and Medline) and China (China National Knowledge Internet and Wanfang) to retrieve related articles published between 2000 and 2014. The MeSH (Medical Subject Headings) search terms were “breast cancer or carcinoma or neoplasms”, “matrix metalloproteinase 9 or MMP-9 or gelatinase B”, and “polymorphism or variant or mutation”, as well as their combinations. The references of identified articles were also searched manually to discover additional eligible studies. When the same authors or laboratory reported several publications on the same issue, only the most recent study was included.

INCLUSION CRITERIA:

Eligibility criteria were: 1) case-control study; 2) cases were histopathologically confirmed and the controls were age-matched; 3) evaluating the association between MMP-9 polymorphisms and breast cancer risk; 4) results presented as odds ratio (ORs) with 95% confidence intervals (CIs); and 5) genotype information of patients and controls can be extracted.

DATA EXTRACTION:

Two experts independently assessed the extracted data of the included studies. The following items from each study were extracted: first author name, publication year, country, ethnicity, total number of breast cancer cases and controls, genotyping method, study design (hospital-based or population-based case-control studies), and the genotype information.

STATISTICAL ANALYSIS:

Pooled ORs with associated 95% CIs were employed to assess the strength of the association between MMP-9 polymorphisms and breast cancer susceptibility. Four genetic models were calculated to evaluate this association: the allele model, the homozygous model, the dominant model, and the recessive model. Statistical heterogeneity between studies was measured by using the Q statistic. A random-effects model was used when the P value was less than 0.1 or I² more than 50%, which was considered statistically significant; otherwise, a fixed-effects model was used. Review Manager 5.2 (the Cochrane Collaboration, Oxford) was used for conducting the statistical analyses. All tests were 2-sided.

Results

STUDY CHARACTERISTICS:

We identified 42 articles that contained our key words. After applying the inclusion and exclusion criteria, we selected 10 articles, including 6177 breast cancer cases and 6726 matched controls. Figure 1 shows the selection process. Of the 10 selected articles, 1 was written in Chinese [20] and 9 in English [17,19,21–27]. Four polymorphisms of MMP-9 were assessed in the present meta-analysis: rs3918242, rs17576, rs2250889, and rs3787268. Table 1 presents the main information of included studies. Table 2 lists the distribution of allele and genotype information for each variant in the included studies.

META-ANALYSIS:

Table 3 shows the results of statistical analysis for each polymorphism of MMP-9. For rs3918242, 6 studies included 1435 breast cancer cases and 1446 controls. The results showed that the frequency of risk allele C was higher in breast cancer patients than in controls (20.8% vs. 17.7%); however, the C allele was not associated with breast cancer risk (T vs. C: OR=1.36, 95% CI=0.91–1.30, P=0.13). This insignificant association was also found in the homozygous model (TT vs. CC: OR=1.43, 95% CI=0.72–2.86, P=0.30) and the dominant model (TT+CT vs. CC: OR=1.38, 95% CI=0.88–2.16, P=0.16). TT genotype in the recessive model significantly increased the risk of breast cancer (TT vs. CT+CC: OR=1.55, 95% CI=1.12–2.16, P=0.009) in a fixed-effects model. Figure 2 showed the association between rs3918242 of MMP-9 and breast cancer risk.

For rs17576, 3 articles, containing 1176 patients and 1142 controls, were included. Overall, no significant association was found between rs17576 of MMP-9 and breast cancer susceptibility under any genetic model (A vs. G: OR=0.88, 95% CI=0.58–1.34, P=0.55; AA vs. GG: OR=0.71, 95% CI=0.27–1.89, P=0.49; AA+GA vs. GG: OR=0.96, 95% CI=0.64–1.43, P=0.84; AA vs. GA+GG: OR=0.72, 95% CI=0.31–1.71, P=0.46) in a random-effects model (Figure 3).

For rs2250889, we identified 2 articles, including 331 cases and 335 controls. There was no evidence of an association between MMP-9 rs2250889 and breast cancer susceptibility in different genetic models (G vs. C: OR=0.61, 95% CI=0.27–1.36, P=0.23; GG vs. CC: OR=1.96, 95% CI=0.09–45.03, P=0.67; GG+CG vs. CC: OR=2.28, 95% CI=0.27–18.95, P=0.45; GG vs. CG+CC: OR=1.10, 95% CI=0.21–5.72, P=0.91) (Figure 4).

For rs3787268, 2 articles were assessed, including 3804 cases and 4387 controls. No significant relationship was found between GG+GA genotype and breast cancer risk in the dominant model (AA+GA vs. GG: OR=0.95, 95% CI=0.71–1.27, P=0.74) (Figure 5).

SENSITIVITY ANALYSIS AND PUBLICATION BIAS:

We deleted each included study 1 at a time to observe whether the single study influenced the overall results. We found that the significance of pooled ORs was not changed when any individual study was omitted, indicating no bias was present. A funnel plot showed no obvious asymmetry (Figure 6), further indicating that there was no possible publication bias.

Discussion

In the present meta-analysis we explored the relationship between MMP-9 polymorphisms and breast cancer susceptibility. Our results suggest that TT genotype in MMP-9 rs3918242 (−1562 C/T polymorphism) had a significant association with increased risk of breast cancer, but other genotypes or variants were not associated with breast cancer risk. This result was in contrast to a meta-analysis conducted by Zhou et al., which found no significant association between any genotype of MMP-9–1562 C/T polymorphism and breast cancer risk [28].

MMP-9 plays an important role in the malignancy and the growth of the tumor [29], and has been linked to cancer cell proliferation, tumor invasion, and epithelial-to-mesenchymal transformation [30]. Rosella et al. summarized and analyzed the role of MMP-9 in different phases of the tumorigenic process, and found that MMP-9 has vital tumor-suppressing functions, promoting inflammatory anti-tumor activity, producing endogenous angiogenesis inhibitors, and inducing apoptosis [31]. Studies have demonstrated that MMP-9 is involved in breast cancer progression and metastasis due to its ability to degrade denatured collagens and type IV collagen, which is associated with the disruption of basement membranes [32].

Merdad et al. showed that MMP-9 is a reliable potential candidate diagnostic biomarker and drug target in breast cancer [33]. Expression of MMP-9 is up-regulated in breast cancer [34], and higher concentrations of MMP-9 proteins were detected in breast cancer tissue compared to normal breast tissue [29]. MMP-9 was also constitutively expressed in some breast tumor cell lines but not in normal breast epithelial cells [35]. MMP-9 expression has prognostic value of overall survival and relapse-free survival in breast cancer patients. Johanna et al. reported that positive stromal MMP-9 expression indicates poor survival in hormone-responsive small tumors, but that MMP-9 expression favors survival in carcinoma cells [36]. A meta-analysis by Song et al. suggested that positive MMP-9 expression confers a higher risk of relapse and worse survival in patients with breast cancer [37].

MMP-9 variants that influence expression may contribute to cancer susceptibility. The -1562 C/T variant was shown to play a functional role in gene transcription, resulting in the loss of binding of a nuclear protein to this region and an increase in transcriptional activity in macrophages. Przybylowska et al. showed that the T allele of MMP-9–1562 C/T was associated with the malignance and the growth of the tumor [29]. MMP-9 R279Q polymorphism was shown to influence the malignant potential of renal cell carcinoma in a Japanese population [38]. However, Beeghly-Fadiel et al. suggested that common genetic variation of MMP-9 was not significantly associated with breast cancer susceptibility among participants of the Shanghai Breast Cancer Genetics Study [39].

The present meta-analysis has several limitations. First, the number of eligible articles was small, which may affect the reliability of the results. Secondly, MMP-9 may act by interacting with other MMPs or their inhibitors. Thirdly, we only analyzed studies from a few populations, so future research needs to include more ethnic groups.

Conclusions

Our results found that TT genotype of MMP-9–1562 C/T polymorphism in the recessive model was significantly associated with increased the risk of breast cancer. However, no significant association was found between other MMP-9 polymorphisms and breast cancer risk. Further well-designed studies with larger populations are needed to further explore the role of MMP-9 polymorphism in breast cancer risk.