Lysyl oxidase G473A (rs1800449) polymorphism influences the risk of cancer progression: a meta-analysis

The genetics of cancer progression is important for the design of optimal therapeutic strategies. Lysyl oxidase (LOX) is a cancer progression gene that has been studied enough to warrant a synthesis of its primary data from association studies. However, reported associations between the LOX G473A (rs1800449) gene polymorphism and cancer have been inconsistent, prompting a meta-analysis so that we could obtain more precise estimates. Database searches of the published literature yielded seven case-control studies. We calculated pooled odds ratios (ORs) and 95% confidence intervals (CIs) using four genetic models: homozygous (H), recessive (R), dominant (D) and codominant (C). Subgroup analysis was based on ethnicity and cancer type. Outlier analysis was used to examine sources of heterogeneity. The strength of evidence was based on the magnitude of effects, high associative significance, consistency and homogeneity. H/R outcomes exerted more associative effects than D/C results. Two reasons for this are as follows: (i) H/R analyses precluded outlier treatment; and (ii) the magnitude of H/R (ORs of > 2.0) was twice that of D/C (ORs > 1.0). All else being equal, significant pooled ORs in all genetic models had high significance (Pa < 10-5). Strong evidence for associations was found in the outcomes for Asian and gastrointestinal (GI) cancers. In summary, the LOX rs1800449 polymorphism confers significant overall susceptibility, particularly in GI cancers, and places Asians at risk.

components (tenascins and collagens) in cancer patients [2][3][4]. Furthermore, increased expression of LOX has been found to significantly correlate with increased metastasis and reduced patient survival in a number of clinical cancer studies [1,5]. Thus, the role of LOX in the metastatic milieu of various cancers [6][7][8][9] renders this protein a useful clinical target [10]. However, clinical differences in mRNA and protein expression attributed to tumor type and tissue specificity warrant caution in the interpretation of associations [10].
The LOX gene has seven exons that encode several functional domains of the LOX protein [11]. LOX undergoes a series of transformations with size changes expressed in kilo Daltons (kDa) from a preproenzyme (46 kDa) to a proenzyme (50 kDa) to a propeptide (18 kDa) and ends up as a functional protein (32 kDa) in the ECM [12]. The LOX gene has an important single-nucleotide polymorphism (SNP) located at exon 1 of chromosome 5q23. 1-q23 (rs1800449). At this location, the open reading frame at position 473 contains the guanine (G)-adenine (A) bases [13]. A shift from 473G to 473A changes the amino acid arginine (Arg) at residue 158 to glutamine (Gln) (Arg158Gln) in the LOX propeptide [11].
Since it was discovered [11], LOX rs1800449 has been extensively studied for its relationship with carcinogenesis [14][15][16][17][18]. At the gene level, single-study reports of LOX rs1800449 associations with cancer have not been consistent. It is thus opportune to statistically synthesize the findings of these studies using meta-analysis. Here, we examine the role of the LOX rs1800449 SNP in the risk of cancer progression, which might guide potential future directions in cancer genetics. To obtain less ambiguous, clearer estimates of the role of SNPs in this investigation, we assessed the strength of evidence using statistical and meta-analytical criteria. This study aims to highlight the genetic role of LOX rs1800449 in cancer progression and to provide important information that could be useful in clinical decision making.

Selection of studies
We searched MEDLINE using PubMed, Google Scholar and Science Direct for association studies as of August 17, 2019. The terms used were "Lysyl oxidase", "LOX", "polymorphism" and "cancer" as medical subject headings and text. References cited in the retrieved articles were also screened manually to identify additional eligible studies.
Inclusion criteria were (i) case-control studies evaluating the association between LOX polymorphisms and cancer risk and (ii) sufficient genotype frequency data presented to calculate the odds ratios (ORs) and 95% confidence intervals (CIs). The exclusion criteria were as follows: (i) reviews; (ii) studies whose control frequencies deviated from the Hardy-Weinberg equilibrium (HWE); (iii) articles that were not case-control studies; and (iv) studies with unusable genotype data.

Data extraction
Two investigators (RM and NP) independently extracted data and arrived at consensus.
The following information was obtained from each publication: first author's name, the year of publication, the country of origin, ethnicity, cancer type, study design, studies that matched their controls with cases and the criteria used, sample sizes and genotype frequencies.
Armonk, NY, USA). Gaussian (normal) distribution (P > 0.05) warranted the use of the mean ± standard deviation (SD). Otherwise, the median (with interquartile range) was used. Using the G*Power program [20], we evaluated statistical power as its adequacy bolsters the level of associative evidence. Assuming an OR of 1.5 at a genotypic risk level of α = 0.05 (two-sided), power was considered adequate at ≥ 80%.

HWE
HWE was assessed with the application in https://ihg.gsf.de/cgi-bin/hw/hwa1.pl. A P-value of < 0.05 indicated deviation from the HWE. Deviations were found in six studies [14][15][16][17][18]21] and were thus excluded from the analysis (Table S1).  Of the 20, 13 were excluded for not conforming to our inclusion criteria. A manual search of the references from the publications yielded no additional articles. provides a detailed description of this meta-analysis (Table S3).

Overall and subgroup analysis
Tables 2 and 3 present 15 significant (P a < 0.05) outcomes, 14 (93.3%) of which had P avalues that reached < 10 -5 , indicating both consistency and strong effects. Table 2 shows all the Fe results with three important features: (i) initial Fe precluded outlier treatment; (ii) H/R outcomes (ORs 2.3-2.5) had twice the magnitude of effect over the D/C results (ORs 1.4-1.6) and (iii) a strong case of LOX rs1800449 associations with cancer based on the core outcomes. Judged on the basis of high significance (P a < 10 -5 ) and homogeneity (I 2 = 0%), we identified four core outcomes (é), which were ranked based on the number of studies (n), with elevated n indicating a higher rank. Thus, the Asian outcome (n = 6) in the C model was ranked first (OR 1.53, 95% CI 1.38-1.70, P a < 10 -5 ). This core finding (Table 2) is the same as the overall outcome seen in the PSO panel for the C model (Table   3), with all Asian subjects. Table 2 shows the subordinate-in-rank results with a collective outcome that identified significant associations in GI cancers (R/D/C: ORs 1.45-2.34, 95% CIs 1.24-3.15, P a < 10 -5 ). The P a -values in these outcomes showed that in Bayesian Factor terms [37], this indicates strong evidence of association, underpinned by study compatibility. Of note, sensitivity treatment rendered robustness to all the highly significant outcomes (Table 4).

Summary of findings
The main findings of this study presented layers of evidence pointing to strong associations between LOX rs1800449 and a risk of cancer progression. These layers included a consistency of effects (the significant ORs were > 1.0 across all comparisons) and high associative significance (93.3% of the comparisons had P a < 10 -5 ). This level of significance enabled the outcomes to survive the Bonferroni correction, attesting to their stability (an added layer) and minimizing the risk of type 1 error (false positives). The outcomes that met the criteria for strong evidence (P a < 10 -5 and I 2 = 0%) were found in the C model (Asian) and the R/D/C models (GI cancers), which comprised our core findings.
These Fe-derived core outcomes were initially homogeneous without the necessity of outlier treatment. One purpose of biomedical meta-analysis is to subject the overall summary effects to meta-analytical procedures (outlier and sensitivity treatments, subgrouping) to test for their stability, consistency and robustness (another added layer).
These features have, for the most part, characterized our findings. Furthermore, ethnicity and subgrouping by cancer type did not materially alter the overall results, both in terms of the direction of association and statistical significance. The lack of material differences (all the significant outcomes indicated increased risks) across comparisons suggests the consistency of our results. Our GI cancer findings, in particular, were noteworthy for their high significance and homogeneity in most genetic models. These significant findings underpin the importance of subgrouping in the evaluation of the risk of disease polymorphisms. Primary study findings about the roles of genetic variants in cancer are not only conflicting but also difficult to replicate. These differences may be due to limited statistical power, heterogeneous subjects, the presence of confounders and population stratification [19].

Comparison with a previous meta-analysis
The previous meta-analysis [31] and ours each comprised seven papers, but only two [33, 36] were common in both. These differences in the five included studies between the two meta-analyses impacted the study design with differential subgroupings (ethnicity and The heterogeneity of these values did not differ between the two meta-analyses. The two insights that we offer from our meta-analysis are (i) attention to study quality and (ii) differential findings from subgroup analysis by cancer type.

The LOX gene and LOX protein in cancer
Metastasis is the last stage of cancer progression that warrants a good understanding of  [ 1] have reported that therapeutic targeting of LOX to prevent metastasis in the preclinical milieu involving inhibitors and function-blocking antibodies has been effective.

Strengths and limitations
Interpreting our meta-analysis findings is better contextualized in terms of their strengths and limitations. The limitation is that the majority (84%) of the studies had Asian subjects, indicating an underrepresentation of other ethnic groups. We had one study each for non-