Atmospheric particulate matter and breast cancer survival: estrogen receptor triggered?

Abstract

To the Editor, Recently, a study has reported the effect of ambient particulate matter (PM) on the outcome of breast cancer in theUSA [1]. The authors indicated that exposure to higher PM was significantly associated with poorer survival, particularly among females diagnosedwith early-stage cancer. Actually solid data and analyses given by several studies have revealed that atmospheric PM is associated with the increased morbidity and mortality of breast cancer patients [2–4]. However, to date, the underlying mechanism was not mentioned and still remains unclear. Atmospheric PM is the major air pollutant found in northern China, including Shandong Province. Our team presented an interesting report a few months ago [5], and the study has been continued. As reported, we previously recruited female patients who had resided in the same cities of Shandong Province for at least 10 years prior to their diagnosis of early-stage breast cancers [5]. Informed consent was obtained from all individual participants included in the study. We only considered PM10 (particulate matter less than 10 μm in diameter) data since previous PM2.5 (particulate matter less than 2.5 μm in diameter) data were impossible to access: these data will not be extensively monitored in China until 2016. Nevertheless, PM2.5 data were contained within the PM10 monitoring data naturally. Moreover, we analyzed the PM10 geographical distribution pattern (Fig. 1a) and reviewed literature describing global estimates of PM2.5 concentrations from satellite-based data, indicating a high consistency of PM2.5 and PM10 geographical concentration distribution over the same time period [6]. Our cigarette-smoking status adjusted logistic regression model only included female patients who were diagnosed with invasive breast cancer (pathological tumor-node-metastasis (pTNM) stages I–III) or ductal carcinoma in situ (DCIS), and the result indicated that patients living in high-PM areas presented with more invasive cancers (p= 0.028, Fig. 1b) with higher tumor grades (p=0.028, Fig. 1c), which is consistent with Hu’s study. Interestingly, we observed a higher ratio of estrogen receptor (ER)-positive cases in patients from high-PM group (p=0.022, Fig. 1d) and noticed that the differences in tumor’s histological grade did originate from ER-positive cases (p=0.003, Fig. 1e), not ER-negative ones (p=0.663, Fig. 1f) [5]. Based on previous findings [5], we conducted survival analyses using Kaplan-Meier curves in ERpositive and ER-negative cases, respectively. All deaths caused by other diseases were considered as censored cases. Our results suggested that exposure to high PMwas significantly associated with poorer recurrence-free survival (RFS) (p=0.019, Fig. 1g) and marginally associated with overall survival (OS) (p=0.083, Fig. 1h) in ER-positive patients, but not in ER-negative cases (p=0.427 for RFS, and p=0.730 for OS, Fig. 1i, j, respectively). Based on our classificationmethod, medium-PMgroup included intermediate cases, a continuum set between the highand the low-PM groups, which means that the characteristics of it may fall in between them. Focused on the subject of this study, we carefully compared the prognostic data between highand lowPM cases only, with its limited sample size. Q. Huo : C. Cai :Q. Yang (*) Department of Breast Surgery, Qilu Hospital of Shandong University, 107 West Wenhua Road, Jinan 250012, Shandong Province, China e-mail: qifengy@gmail.com