RESULTS
Search results and characteristics of studies included
Of 862 potentially relevant articles, 846 articles were excluded due to duplication or the title and abstract not meeting inclusion criteria. Subsequently, 11 articles were excluded because of data duplication or lack of the outcomes of interest. Finally, five cohort studies met all inclusion criteria.10–13,20 One of them was a single-arm cohort study regarding MI and only provided cancer incidence rate. The rest of the studies supplied overall or subgroup effect estimates (OR, RR, HR, or SIR) with 95% CI. The literature retrieval, review, and selection process are shown in Figure 1. The characteristics of cohort studies are shown in Table 1. The quality assessment of observational studies was performed by NOS quality scale (Table 1). Quality assessment results suggested observational studies included had moderate or high quality, which might lead to heterogeneity and risk of bias.
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(To view a larger version of Table 1, click here.)
Meta-analysis results
Cancer risk after MI
Four studies with 221,994 MI patients were included to estimate the incidence rate of cancer among patients with MI history.10,12,13,20 The pooled cancer incidence rate in MI patients was 9.5% (8.3%–10.7%, Figure 2), which was comparable to that in non-MI controls (11.1%; 95% CI=7.3%–14.8). Three studies reported the overall effect estimates in patients with MI.10,12,13 Pooled analyses of OR in the random-effects model showed that the increased cancer risk in patients with MI in comparison with controls had no statistical significance, and the heterogeneity among studies was high (OR=1.08; 95% CI=0.97–1.19, P=0.153; I2=90.8%; P for heterogeneity <0.01; Figure 3).
Subgroup analysis by gender
Subgroup effect estimates based on gender were presented in four studies.10–13 Pooled analyses of OR in random-effects model demonstrated that the overall risk of cancer incidence in male patients with MI was nonsignificant (OR=1.04; 95% CI=0.99–1.10, P=0.124; I2=78.5%; P for heterogeneity <0.01; Figure 4A). However, female patients with MI had a significantly increased risk of incident cancer (OR=1.10; 95% CI=1.01–1.20, P=0.025; I2=82.9%; P for heterogeneity <0.01; Figure 4B).
Subgroup analysis by cancer type
Three studies reported the outcome of cancer types or sites.10,11,13 Although there was much difference in the classification of cancers in these studies, all of them provided the gender-stratified incidence of lung, prostate, and breast cancers. We found lung cancer risk was significantly increased both in male (OR=1.12; 95% CI=1.05–1.19, P<0.01; I2=38.6%; P for heterogeneity =0.196; Figure 5A) and female (OR=1.51; 95% CI=1.15–1.99, P<0.01; I2=92.0%; P for heterogeneity <0.01; Figure 5B) patients with MI history. However, the increased risk of sex-specific cancers including prostate cancer (OR=0.96; 95% CI=0.85–1.09, P=0.546; I2=94.4%; P for heterogeneity <0.01; Figure 5C) and breast cancer (OR=0.94; 95% CI=0.86–1.04, P=0.222; I2=39.9%; P for heterogeneity =0.189; Figure 5D) had no statistical significance.
Subgroup analysis by follow-up time
Only two studies revealed the incidence of cancer in subjects with MI by time after the MI event.12,13We observed the increased cancer risk was only significant in the first 6 months after MI with no heterogeneity (OR=1.93; 95% CI=1.42–2.63, P<0.01; I2=0%; P for heterogeneity =0.606; Figure 6A). After 6 months, the increased cancer risk vanished, which was reflected by the pooled ORs for 6 months to 1-year (OR=1.03, 95% CI=0.92–1.15, P=0.627; I2=0%; P for heterogeneity =0.786; Figure 6B) and >1-year (OR=0.98, 95% CI=0.93–1.04, P=0.585; I2=0%; P for heterogeneity =0.487; Figure 6C) follow-up after MI.
Evaluation for publication bias
Begg’s and Egger’s tests were performed to evaluate publication bias. For the overall cancer risk analysis of MI vs control, there was no significant publication bias (Begg’s test, P=0.602; Egger’s test, P=0.816).
