Can Aspirin Use Be Associated With the Risk or Prognosis of Bladder Cancer? A Case-Control Study and Meta-analytic Assessment

Aspirin, widely used to prevent cardiovascular disease, had been linked to the incidence of bladder cancer (BCa). Existing studies focusing on Chinese populations are relatively rare, especially for Northeast China. Meanwhile, relevant studies on the effects of aspirin on the occurrence or prognosis of BCa are inconsistent or even controversial. First, in the case control study, logistic regression analysis was used to investigate the association between aspirin intake and risk of BCa including 1121 patients with BCa and the 2242 controls. Subsequently, Kaplan-Meier curve and Cox regression analyses were applied to explore the association between aspirin intake and clinicopathological factors which may predict overall survival (OS) and recurrence-free survival (RFS) of BCa patients. Finally, we quantificationally combined the results with those from the published literature evaluating aspirin intake and its effects on the occurrence, outcome of surgery and prognosis of BCa by meta-analysis up to May 1, 2021.Our case-control study demonstrated that the regular use of aspirin was not associated with a reduced incidence of BCa (P=0.175). Stratified analyses of sex showed that aspirin intake did not lead to a lower risk of BCa in female patients (P=0.063). However, the male population who regularly took aspirin had a lower incidence of BCa (OR=0.748, 95% CI= 0.584-0.958, P=0.021). Subgroup analyses stratified by smoking found a significant reduction in the risk of BCa in current smokers with aspirin intake (OR=0.522, 95% CI=0.342-0.797, P=0.002). In terms of prognosis of BCa, patients with a history of aspirin intake did not had a markedly longer OS or RFS than those with no history of aspirin intake by Kaplan-Meier curves. Stratified analysis by sex showed no correlation between aspirin intake and the recurrence or survival of BCa for either male or female patients. However, in people younger than 68, aspirin intake seemed to have prolonged effects for overall survival (HR=3.876; 95% CI=1.326-11.325, P=0.019). Then, we performed a meta-analysis and the combined results from 19 articles and our study involving more than 39524 BCa cases indicated that aspirin intake was not associated with the occurrence of BCa (P=0.671). Subgroup analysis by whether regular use of aspirin, by the mean duration of use of aspirin, by sex, by smoking exposure, by research region and by study type also supported the above results. In terms of the impact of aspirin intake on the prognosis of patients with BCa, 11 articles and our study involving 8825 BCa cases were eligible. The combined results showed that patients with aspirin intake did not have significantly influence on survival, recurrence, progression and metastasis than those without aspirin intake. On the whole, both our retrospective study and literature meta-analysis suggested a lack of a strong relevant association between the use of aspirin and the incidence or prognosis of BCa. Thus, additional long-term follow-up prospective research is warranted to clarify the association of aspirin with BCa incidence and prognosis.

Aspirin, widely used to prevent cardiovascular disease, had been linked to the incidence of bladder cancer (BCa). Existing studies focusing on Chinese populations are relatively rare, especially for Northeast China. Meanwhile, relevant studies on the effects of aspirin on the occurrence or prognosis of BCa are inconsistent or even controversial. First, in the case control study, logistic regression analysis was used to investigate the association between aspirin intake and risk of BCa including 1121 patients with BCa and the 2242 controls. Subsequently, Kaplan-Meier curve and Cox regression analyses were applied to explore the association between aspirin intake and clinicopathological factors which may predict overall survival (OS) and recurrence-free survival (RFS) of BCa patients. Finally, we quantificationally combined the results with those from the published literature evaluating aspirin intake and its effects on the occurrence, outcome of surgery and prognosis of BCa by meta-analysis up to May 1, 2021.Our case-control study demonstrated that the regular use of aspirin was not associated with a reduced incidence of BCa (P=0.175). Stratified analyses of sex showed that aspirin intake did not lead to a lower risk of BCa in female patients (P=0.063). However, the male population who regularly took aspirin had a lower incidence of BCa (OR=0.748, 95% CI= 0.584-0.958, P=0.021). Subgroup analyses stratified by smoking found a significant reduction in the risk of BCa in current smokers with aspirin intake (OR=0.522, 95% CI=0.342-0.797, P=0.002). In terms of prognosis of BCa, patients with a history of aspirin intake did not had a markedly longer OS or RFS than those with no history of aspirin intake by Kaplan-Meier curves. Stratified analysis by sex showed no correlation between aspirin intake and the recurrence or survival of BCa for either male or female patients. However, in people younger than 68, aspirin intake seemed to have prolonged effects for overall survival (HR=3.876; 95% CI=1.326-11.325, P=0.019). Then, we performed a meta-analysis and the combined results from 19 articles and our study involving more than 39524 BCa cases indicated that aspirin intake was not associated with the occurrence of BCa (P=0.671). Subgroup analysis by whether regular use of aspirin, by the mean duration of use of aspirin, by sex, by smoking exposure, by research region and by study type also supported the above results. In terms of the impact of aspirin intake on the prognosis of patients with BCa, 11 articles and our study involving 8825 BCa cases were eligible. The combined results showed that patients with aspirin intake did not have significantly influence on survival, recurrence, progression and metastasis than those without aspirin intake. On the whole, both our retrospective study and literature meta-analysis suggested a lack of a strong relevant association between the use of aspirin and the incidence or prognosis of BCa. Thus, additional long-term follow-up prospective research is warranted to clarify the association of aspirin with BCa incidence and prognosis.
Keywords: urinary bladder neoplasms, aspirin, risk, prognosis, case-control, meta-analysis BACKGROUND Bladder cancer (BCa) is the 11th most common cancer in the world. The global age-standardized incidence rate per 100,000 persons/year is 2.2 for women and 9.0 for men (1,2). According to the National Cancer Institute, the estimated numbers of new BCa cases and deaths in the USA alone (2014) will be 74,690 and 15,580, respectively (3,4). In China, the incidence and mortality rates have increased gradually in the past few years. According to the National Central Cancer Registry (NCCR) of China 2015 annual report, the overall incidence of BCa was 7.68/10 5 (5,6). Among patients with superficial or non-muscle invasive tumors after transurethral resection or perfusion therapy, 70% would experience recurrence, and 10% to 20% would show progression to muscle-invasive tumors (7,8). Due to the unfavorable prognosis of muscle-invasive cancer, the treatment involves multiple modalities, including radical surgery, radiotherapy, and chemotherapy. However, nearly half of these patients develop metastases and die within 3 years (7,9). The occurrence or recurrence of BCa is a molecular biological change or process that is effected by occupational factors, nonoccupational factors, and genomics and proteomics factors (10) Other non-occupational factors, including cigarette smoking (11), drinking water used for washing or cleaning drinking water used for washing or cleaning (12) the consumption of substances with nitrate and nitrite content (13), alcohol consumption (14), and special drug intake (15,16), have also been associated with BCa but are less well established. Therefore, early detection strategies and prognosis monitoring are essential for reducing mortality from BCa.
Aspirin, a typical non-steroidal anti-inflammatory drug, has been widely used for pain, fever and cardiovascular disease (17,18) In recent years, a large accounts of studies have suggested that aspirin has a potential preventive effect in several types of cancers (18)(19)(20). The antitumor activity of aspirin is thought to be based mainly on two different mechanisms. First, aspirin may interfere with carcinogenesis by inhibiting the target of cyclooxygenase (COX), which is produced in response to inflammation and leads to angiogenesis and reduced apoptosis.
As one of isoforms of cyclooxygenase, the level of COX-2 may not only increase the malignant properties of BCa cells but also be related to high-grade and advanced-stage BCa patients (21,22). Second, aspirin plays roles in promoting apoptosis or inhibiting the proliferation of tumor cells by interfering with the pathway independent of COX-2 as an anticancer agent. Aspirin inhibits the growth of PI3K mutant breast cancer by activating AMP-activated protein kinase (AMPK) and inhibiting mechanistic target of rapamycin complex 1 (mTORC1) signaling independent of COX-2 and IKK-b/NF-kB (23). Furthermore, aspirin inhibited the proliferation of neuroblastoma cells, upregulated p21Waf1 and regulated Rb1 to promote differentiation through a Cox-independent mechanism (24).
Since aspirin has apparent preventive effects on other tumors, its role in BCa has also received attention. The findings of the impact of aspirin intake and the incidence and mortality of BCa have been inconclusive. Moreover, few studies on the relationship between aspirin intake and BCa in mainland China, especially in Northeast China. To explore whether the use of aspirin is associated with altered risk of BCa, we conducted a case-control study by enrolling 1121 patients with BCa. To avoid bias from single-center study results, we further completed a meta-analysis of eligible literature by searching electronic journals or databases for documents before March 1, 2021. The connection between aspirin intake and the incidence and prognosis of BCa was investigated, which helps to further determine whether the use of aspirin has a preventive effect on BCa. Our analysis provides a basis for further exploration of the role of aspirin in the future. average age 68 years old, ranging from 49 to 84 years. The control group comprised of 2242 individuals without a bladder cancer diagnosis during the study period, which were hospitalized in the department of respiratory, gastroenterology, orthopedic surgery, dermatology, and cardiology, etc.
Patients in both groups underwent 1:2 matching based on sex, age, and follow-up period at the index date of each case. The possible risk factors for the occurrence of BCa, including age, marital status, smoking status, alcohol use, aspirin use, metformin use, history of cardiovascular disease, history of cerebrovascular disease and history of diabetes were extracted from clinical history information.
Study Population for Exploring Association of Aspirin Intake and Prognosis of Bladder Cancer 1121 patients in the case group who were pathologically diagnosed with bladder cancer by pathological biopsy or surgical biopsy at the Second Affiliated Hospital of Dalian Medical University were included in the study. The clinical and pathological baseline data, including age, gender, histological grading, T stage, lymph node metastasis, distant metastasis, type of surgery were recorded. TMN staging and histological grading were determined according to the 2004 WHO/ISUP classification. Recurrence of bladder cancer is defined as visual and/or biopsy evidence of a tumor confirmed by cystoscopy or urine cytology.

Assessment of Aspirin Use
Aspirin users were defined as those who used at least 81mg aspirin daily at least twice a week for 1 month or more. Nonusers are subjects who had never used the drug or had used it for <1 month. The average daily dose of aspirin for each aspirin user was also obtained by dividing the cumulative dose of aspirin by the cumulative number of days of aspirin use. The indication for the use of aspirin (i.e., analgesic or cardiovascular disease, cerebrovascular disease prevention) was also recorded (25)(26)(27). Patients were stratified according to aspirin intake for most (50% or more) of the interval between diagnosis and the date of the first tumor recurrence or last follow-up. The exclusion criteria were as follows: (1). Unable to obtain accurate medication records, demographic data, or patient characteristics. (2). Identification of a history of exposure to carcinogens. (3). Patients on clopidogrel, warfarin, or statins alone or in combination with other fibrin clotting inhibitors. (4). Aspirin use was contraindicated.

Statistical Analysis
SPSS version 13.0 (SPSS Inc., Chicago, USA) was used for analysis. The associations between aspirin intake and clinicopathological parameters were evaluated by the chisquare test. Continuous data and frequency data were analyzed by t test and Fisher's exact test. When the independent variables were screened in order to investigate the risk factors for the occurrence of BCa, adjusted odds ratios (ORs) or relative risks (RRs) and the corresponding 95% confidence intervals (CIs) were calculated by univariate and multivariate logistic regression analysis. By univariate analysis, those with a significant P value less than 0.05 in this test were included in the multivariate regression analysis. To evaluate the overall survival (OS) which was the interval from surgery to death and recurrence-free survival (RFS) which was the interval from surgery to intravesical recurrence in patients with BCa, the Kaplan-Meier curve and log-rank test were used. After assessing clinicopathologic factors by univariate Cox regression model, statistically significant variables were put into multivariate Cox regression analysis to find independent prognostic factors for OS and RFS. After SPSS analysis, the P value of the above parameters was obtained. A P-value less than 0.05 was considered statistically significant.

Search Strategy
The implementation of this meta-analysis was conducted based on the "Preferred Reporting Items for Systematic Reviews and Meta-Analyses" (PRISMA) guidelines. The PRISMA checklist was shown in Table 1. Our meta-analysis has been already registered of the review protocol on PROSPERO (CRD42021245411). The study retrieved articles from the PubMed, Embase, Ovid Medicine, Cochrane Library and Scopus databases published before May 1, 2021, to identify relevant studies evaluating aspirin intake and its effects on the occurrence and prognosis of BCa using the following medical subject headings that include all spelling variations: "bladder cancer" and "aspirin", "occurrence", "risk" and "prognosis", "survival" and "recurrence". Without national and linguistic restrictions, after reviewing the duplicate data, the two reviewers independently screened the titles and abstracts, excluding articles that were not associated with our research, reviews, and related animal experiments and maximizing data quality.

Selection Criteria
Studies satisfying the following criteria were included in our analysis: (1) the histologic type of the tumors was urothelial carcinoma of the bladder by histologic or pathologic examination; (2) the association between aspirin intake and the risk of BCa or prognosis of patients with BCa was investigated; and (3) sufficiency of data for the calculations of OR/RR/hazard ratio (HR), 95% CI and P-value. Accordingly, the following exclusion criteria were applied: (1) studies in the form of reviews, letters to the editor, commentaries, or case reports that lacked original data; (2) molecular biology research that explored the impact of aspirin on cancer cell lines and animal models; and (3) studies in which the HR/OR/RR and its standard error could not be collected based on the given information.

Data Extraction
After the full-text evaluation, the two authors extracted the data separately for further qualitative and quantitative analysis to increase the authenticity of the data. For the selected articles, we extracted data from each study, including the first author, publication time, region, type of study, study period the number of participants and BCa cases, age, the usage of aspirin, HR/OR/RR, and adjustment factors. Describe method of data extraction from reports (e.g., piloted forms, independently, in duplicate) and any processes for obtaining and confirming data from investigators. 3

Data items 11
List and define all variables for which data were sought (e.g., PICOS, funding sources) and any assumptions and simplifications made. 3

Risk of bias in individual studies
12 Describe methods used for assessing risk of bias of individual studies (including specification of whether this was done at the study or outcome level), and how this information is to be used in any data synthesis. Figure 1 Summary measures 13 State the principal summary measures (e.g., risk ratio, difference in means). 5 Synthesis of results 14 Describe the methods of handling data and combining results of studies, if done, including measures of consistency (e.g., I 2 ) for each meta-analysis.

5
Risk of bias across studies 15 Specify any assessment of risk of bias that may affect the cumulative evidence (e.g., publication bias, selective reporting within studies).

5
Additional analyses 16 Describe methods of additional analyses (e.g., sensitivity or subgroup analyses, meta-regression), if done, indicating which were pre-specified.

Study selection 17
Give numbers of studies screened, assessed for eligibility, and included in the review, with reasons for exclusions at each stage, ideally with a flow diagram.
8; Figure 2 Study characteristics 18 For each study, present characteristics for which data were extracted (e.g., study size, PICOS, follow-up period) and provide the citations. Tables 7-9 Risk of bias within studies 19 Present data on risk of bias of each study and, if available, any outcome level assessment (see item 12). 5; Figure 1 Results of individual studies 20 For all outcomes considered (benefits or harms), present, for each study: (a) simple summary data for each intervention group (b) effect estimates and confidence intervals, ideally with a forest plot. Summarize the main findings including the strength of evidence for each main outcome; consider their relevance to key groups (e.g., healthcare providers, users, and policy makers).

18, 19
Limitations 25 Discuss limitations at study and outcome level (e.g., risk of bias), and at review-level (e.g., incomplete retrieval of identified research, reporting bias).

Conclusions 26
Provide a general interpretation of the results in the context of other evidence, and implications for future research.

Funding 27
Describe sources of funding for the systematic review and other support (e.g., supply of data); role of funders for the systematic review.

Quality Assessment
The quality assessment used the most recent version of the risk of bias tool recommended in the ROBINS-I checklist (28) for systematic reviews of interventions for the included studies. Our selected studies were assessed for bias due to confounding, selection bias, intervention measurement, missing data bias, outcome measurement, reporting bias, and other types of bias. As shown in Figure 1, the risk of bias of our meta-analyses measured by ROBINS-I framework for individual studies was generally low to moderate.

Sensitivity Analysis
Whether influential studies needed to be secondary for exclusion from our meta-analysis was determined by sensitivity analysis. The robustness of the pooled estimates with respect to the employed individual investigations was evaluated using the leave-one-out method based on the Q-test. Lower heterogeneity was determined after eliminating the indicated studies if the P Q value > 0.05. Conversely, low heterogeneity was calculated by removing a single study, indicating that the selected studies did not contribute to the heterogeneity of the overall meta-analysis.

Statistical Analysis
The Stata 12.0 statistical software package (Stata Corp, College Station, TX, USA) was used for all data analyses. We calculated the OR/RR/HR with a 95% CI. The Q-test was used to assess the statistical heterogeneity and judge the pvalue qualitatively. The I 2 value in the I 2 test describes the proportion of the total variation due to heterogeneity rather than sampling errors, and I 2 > 50% or P<0.05 indicates a high degree of heterogeneity. The random-effects model was used; otherwise, there was no heterogeneity, and the fixed-effects model was used. The potential bias was assessed by a funnel plot and Egger's test, and when the funnel plot was symmetrically distributed, there was no significant bias. Conversely, if the funnel plot exhibits skewness and asymmetry, this indicated bias.

The Association of Aspirin Intake and Risk of Bladder Cancer
Among the controls and the cases identified as BCa, the patients who used aspirin accounted for 10.1% of the total number of patients with BCaand 11.6% ofthecontrolgroup. As shownin

Study Identification and Selection
The selection process following the Preferred Reporting Items for Systematic Review and Meta-Analysis (PRISMA) reporting guideline for the association of aspirin intake with the risk and prognosis of BCa is presented in Figure 2. Initially, the database search retrieved 1107 relevant publications. After screening the titles, abstracts and full texts of these articles, we excluded duplicate studies and other studies for various reasons (reviews/editorials, animal/molecular biology studies, or not relevant to our analysis etc.). Thus, in the final analysis, we included 19 studies about the relation of aspirin intake risk of  BCa, 4 studies about outcome of BCa surgery and 11 studies about the relation of aspirin intake and prognosis of patients with BCa based on the inclusion criteria.

The Association Between Aspirin Intake and the Risk of Bladder Cancer
Overall Analysis 31 studies reported the effect estimates of the association between aspirin intake and the occurrence of BCa. The fixed-effects model was applied because the test for heterogeneity was not significant (I 2 =0.00%, P=0.586). We found that patients with aspirin intake did not have a significantly lower risk of BCa than those without aspirin intake (RR=1.007, 95% CI=0.975-1.041, P=0.671). The sensitivity analysis demonstrated that no single trial had significantly influenced the pooled RR ( Figure 3). This result   Figure 3B). However, low dose (<100mg/day) aspirin intake impacted on risk of BCa (RR=1.072, 95% CI=1.004-1.145, P=0.038).

Sensitivity Analysis
The effects for heterogeneity of each study were evaluated by leave-one-out sensitivity analysis. As shown in Figure 4A, the forest plots were equally applied, indicating that the identified studies in our meta-analysis had no significant influence to heterogeneity. Additionally, the respective values of I 2 and P Q were enriched in Figure 4B. There were low heterogeneity after leaving the individual single study out, suggesting that the metaanalysis based on the pooled studies was credible.

Subgroup Analysis by Whether Regular Use of Aspirin
Fixed-effects model was applied on account of little heterogeneity (I 2 =0.8%, P=0.451). There were no dependency between aspirin use and BCa in the group of regular users (RR=1.012,    Figure 5).

Subgroup Analysis by the Mean Duration of Use of Aspirin
Random effects model has been arranged because of strong heterogeneity (I 2 =75.1%, P<0.001). The crowd with a mean   Figure 6).

Subgroup Analysis by Smoking Exposure
Smoking exposure in bladder cancer risk assessment is extremely necessary. There was no testimony for heterogeneity (I 2 =0.0%,   Figure 8).

Subgroup Analysis by Research Region
Meta-analysis using a fixed-effects model (I 2 =0.0%, P=0.590) suggested that aspirin intake had no significant influence on the prevention of BCa in multi-regions (RR=0.974, 95% CI=0.  Figure 9).

The Association Between Aspirin Intake and Outcomes of Surgery for BCa The Association Between Aspirin Intake and Intraoperative Conditions in Patients With BCa
Four studies suggested the relationship between aspirin intake and intraoperative conditions, including mean loss of hemoglobin, mean duration of operation and blood transfusion rate. The low and moderate heterogeneity was observed in blood transfusion rate group (I2=0.0%, P=0.814) and the mean duration of operation (I2=68.0%, P=0.08) group, using fixedeffects models; while high heterogeneity was determined in exploring the association between aspirin intake and the mean loss of hemoglobin (I2=81.0%, P=0.006) for BCa patients, and a random-effects model was applied. Compared with control group, aspirin intake had no impact on loss of hemoglobin with a combined MD of 0.08 (95% CI=-0.32-0. 48

The Association Between Aspirin Intake and Postoperative Complications in Patients With BCa
Three studies suggested the relationship between aspirin intake and postoperative complications including incidence of anycause rehospitalization and hemostatic operation. As low heterogeneity was detected in any-cause rehospitalization (I2=65.4%, P=0.056) and hemostatic operation (I2=0.0%, P=0.577) groups, fixed-effects models were used. Compared to control group, aspirin intake had no impact on incidence of any-cause rehospitalization (RR=1.12, 95% CI=0. 80 Among 11 articles and our study including a total of 8825 BCa patients with survival data, 6 studies investigated the relationship between aspirin intake and overall survival (OS) in BCa patients, and 4 studies reported cancer-specific survival (CSS). The random-effects model was used (Figure 12), as higher heterogeneity was detected among these studies (P-value for heterogeneity<0.001; I 2 =73.5%    Figure 13A. This result exhibited a low probability of publication bias, as determined by Egger's test (P=0.798, Figure 13B).

DISCUSSION
Aspirin is a non-steroidal anti-inflammatory drug with a long history. It is suitable for antipyretic and analgesic use and is widely used in the prevention of cardiovascular thrombosis (18). Recent studies have found that the long-term regular use of aspirin can significantly reduce the incidence of colorectal cancer, gastric cancer, liver cancer and other malignant tumors and improve the survival of patients with its anticancer effects (62)(63)(64)(65). A population-based case-control study analyzed data from 1121 BCa cases and 2242 controls in New Hampshire and found that aspirin significantly reduced the risk of BCa, especially for tumors containing TP53 mutations (33). Similarly, Castelao J et al. (31) illustrated that there was a  P<0.001), regular use of aspirin was not associated with a reduced risk of BCa (P=0.175). As studies of aspirin use and the risk of BCa have yielded mixed results, we further conducted meta-analyses and found that patients with aspirin intake did not have a significantly lower risk of BCa than those without aspirin intake after combining nineteen included articles and our study with more than 39524 BCa patients (P=0.671). Subgroup analysis by whether regular use of aspirin, by the mean duration of use of aspirin, by sex, by smoking exposure, by research region and by study type suggested that aspirin intake had no significant influence on the prevention of BCa. Interestingly, in our case control study, subgroup analyses stratified by sex showed that there was no correlation between aspirin intake and the risk of BCa in female patients, however, the male population who regularly took aspirin had a lower incidence of BCa (OR=0.748; P=0.021). While considering the limited sample size and ethnic specificity, several explanations may help us better understand the above result. Androgens/ Androgen Receptor (AR) system is considered as a central link to physiology and behaviors in male. Similarly, the development of clinical pathology of male malignant tumors could originate from this system (66). There were several studies identifying high expression of ARs in bladder cancer, suggesting that ARs could act as potential markers for monitoring and regulating malignant biological behaviors of BCa including metastasis, and recurrence (67,68). The possible mechanisms contain DNA damage repair, promotion of p53 signaling, or activation of EGFR/ERBB2 pathway, etc. (69). As a mainstream therapy for advanced prostate cancer, androgen deprivation therapy (ADT) was founded having important potential in improving survival of bladder cancer, particularly non-muscle-invasive BCa (70). To our knowledge, antagonist of ARs, consisting of cyproterone, enzalutamide, docetaxel and so forth, is common medicine in ADT. Among these, as a potential application of ADT, aspirin could decrease the mRNA and protein expression of ARs, which has dose-dependence and time-dependence (71). Thereupon, we speculate that in male population, aspirin maybe significantly down-regulate ARs to inhibit the Androgens/Androgen Receptor system and subsequently suppress incidence of BCa, which need further molecular biological validation.
Meanwhile, it should be noted that subgroup analyses stratified by smoking status in our case control study found a significant reduction in the risk of BCa in current smokers with aspirin intake (OR=0.522; P=0.002), not in nonsmokers (P=0.252) or former smokers (P=0.807). Smoking and daily aspirin use are both risk factors for cancer. Some research indicates that aspirin usage in smokers is correlated with an increased risk of developing cancer, which could nullify the protective function of aspirin (72)(73)(74). Wang X et al. (73). found that aspirin use was related to a 29% lower CRC risk among never-smokers, compared to 17% lower CRC risk among smokers above median pack-years, indicating that heavy smokers could not be more favorable for protective role of aspirin against colorectal cancer than non-smokers. As cigarette was found to be more strongly associated with colorectal carcinoma which arise from serrated polyp pathway related to microsatellite instability, it was related to an increased risk of polyps in the left colon (75). While aspirin intake lowered the risk of serrated polyps in the right colon, indicating different subsites of colon cancer may be influenced by.aspirin and smoking (75). As playing role on platelet hyper-reactivity, smoking was strongly associated with increased risk of aspirin resistance, suggesting that the effect of aspirin may rely on independent carcinogenesis or progression (76) pathways of colorectal carcinoma among smokers and non-smokers. In breast cancer, cigarette smoking and aspirin/NSAID use interacted to affect breast cancer-specific mortality. Slattery ML et al. (76) reported that the strongest associations were observed for the interaction between cigarette smoking and aspirin intake with JAK/STAT signaling pathway including JAK2, STAT3, STAT5a, and STAT5b which were critical for cell development, cell proliferation, and apoptosis of breast cancer. As SOCS suppressed the signaling. Nicotine which were found in cigarette smoke condensates and activated the JAK2/STAT3 pathway (77), rs3816997 of SOSC2 may interacted with cigarette smoking and aspirin intake.
The prognostic value of aspirin use on monitor the intraoperative and postoperative outcome of BCa patients was also attracted increasing attention from scholars. After follow up 1121 BCa patients, we did not find that patients with a history of aspirin intake had a markedly longer overall or recurrence-free survival than those with no history of aspirin intake. Cox regression model did not indicate a history of aspirin intake was not an independent factor for overall or recurrence-free survival. Stratified analysis by sex showed no correlation between aspirin intake and the recurrence or survival of BCa for either male or female patients. Interestingly, we found that aspirin intake (HR=3.876; P=0.019) and type of surgery (HR=1.685; P=0.010) were significantly associated with overall survival in BCa patients younger than 68 years old. In the people who regularly used aspirin, majority of them has the history of coagulation abnormalities, consisting of platelet abnormalities and fibrinolysis (78)(79)(80). And coagulation abnormalities have long been closely related with the cardiovascular or cerebrovascular diseases, which are mostly found in the elderly and increased overall mortality considerably (81,82). In addition, various of selection for statistics method may cause discrepancy the analysis outcomes.
Relative to our negative result about the effects of aspirin on tumor recurrence, a case-control study from Italy and a retrospective study from the USA showed a significant association between aspirin and recurrence in patients with BCa (55,61). In the study of Gee JR (55), the 5-year RFS of aspirin users was 64.3%, which was significantly higher than that of non-aspirin users (26.9%), even after multivariate analysis adjusted for other factors. Considering the effect of aspirin on the survival rate of cancer patients, Lyon TD's study (59) found that daily aspirin significantly improved survival outcomes after radical resection. It has also been observed that patients receiving low-dose aspirin had significantly better outcomes than patients receiving high-dose aspirin and those without aspirin. In contrast, a cohort study from the United States found no significant association between aspirin use and the overall survival of BCa patients (52). In addition, a prospective study by Singla N et al. (58) showed that the use of aspirin does not affect the survival of patients with any tumors, including CSS, OS, recurrence-free survival and cystectomy-free survival, regardless of the dose (81 or 325 milligrams a day). In response to these mixed findings, we performed a metaanalysis to investigate the impact of aspirin intake on the prognosis of patients with BCa and found that aspirin had no significant effects on the OS and CSS of BCa patients. In addition, patients with aspirin intake did not have a significantly lower risk of BCa recurrence, progression and metastasis than those without aspirin intake. We also found that there was no difference in blood transfusion rate, loss of hemoglobin, mean duration of operation, any-cause rehospitalization and incidence of any-cause rehospitalization during the resection of BCa between the aspirin group and the control group. Until now, available data have not supported a connection between aspirin exposure and the intraoperative situation and postoperative prognosis of BCa patients despite few prior studies.
Our limitations are as follows: one limitation is that this casecontrol study is a single-center study, which may lead to certain bias or heterogeneity. To the greatest extent possible to avoid such shortcomings or loopholes, we performed a meta-analysis to investigate the relationship between aspirin intake and the risk and prognosis of BCa. Some included studies did not provide available values of HR, RR or OR from multivariate analysis, so we performed calculations from the univariate data and compared them through formula calculations. The statistical methods we used cannot replace all the research methods. The conclusions we obtained without correlation are limited to the scope of our research, which may have some statistical errors (83,84). Second, we only focused on researching patients who regularly consumed aspirin. Due to the limited available information from clinical data, stratification analysis according to different doses or durations was not conducted. The above factors may influence the results regarding the connection between the risk of BCa and the use of aspirin (10), which will be one of the focuses of our future research. Third, both our casecontrol study and meta-analysis showed no differences between aspirin intake and the risk and prognosis of BCa. However, previous in vitro studies have shown that aspirin may play a role as a chemopreventive agent in the OH-BBN/BDF BCa model (85), which suggests that there is heterogeneity between human epidemiological experiments and in vitro cell experiments.

CONCLUSION AND OUTLOOK
Although aspirin has been predicted to be protective against various of tumors, differences in tumor origin and tissue specificity are bound to influence the results, which needed virtual simulated human microenvironment to explore whether aspirin can prevent or monitor BCa. Meanwhile, multi-center, large-sample, prospective studies are also needed. Advances in cancer biology clearly indicate that the development of malignant tumors is the result of complex interactions and the integration of gene expression, proteome and metabolome changes, involving genetics, microbes, diet, drugs (86,87), and other factors such as different living conditions, exposure factors and ethnic differences (88). In the age of precision oncology, individual cancer treatment should be personalized based on genetic and environmental factors. In addition, aspirin, as a sensitizer, can increase the therapeutic effect of chemotherapy for cancers of the colon and stomach, while there are few studies in the urinary system, which will be a promising research direction. As a continuation of this study, it is necessary to further explore pathological examinations, immune parameters, tumor molecular markers and other aspects from the database, which contributes greatly to the development of BCa treatment.

DATA AVAILABILITY STATEMENT
The datasets generated for our case-control study are available on request to the corresponding authors. Additionally, publicly available datasets for meta-analysis in our study could be searched in the PubMed, Embase, Ovid Medicine, Cochrane Library and Scopus databases.

ETHICS STATEMENT
This study was approved by the institutional review committee of the Second Affiliated Hospital of Dalian Medical University and written informed consent was obtained from each patient or their next of kin (Approval Ref. No. KY2018-120).

AUTHOR CONTRIBUTIONS
BF, XL, and GW contributed to the study concept and design, undertook project leadership and guaranteed this work. YH, HL, HJ, MFS, ST, WX, QL, TH, ZY, and RZ were responsible for data collection and interpretation. ZY and RZ controlled quality of data and algorithms. BF, AM, YH, HJ, and ST analyzed data and interpreted the data. BF, GW, HL, HJ, and MS wrote the first draft of the manuscript. BF, HY, and AM reviewed and revised the manuscript. All authors contributed to the article and approved the submitted version.