Distribution of dyslipidemia in Chinese early breast cancer patients at diagnosis and comparison of dyslipidemia incidence following different endocrine therapies: a population-based cohort study

Dyslipidemia increases the risk of cardiovascular disease death in breast cancer (BC). Based on the large West China Hospital (WCH) BC cohort, we aimed to clarify dyslipidemia prevalence at diagnosis and compare the risk of dyslipidemia induced by different endocrine and menopause status. 5917 EBC female patients recorded in WCH BC cohort, diagnosed between 2008.10 and 2017.04, were included for baseline analysis. 1883 patients receiving endocrine therapy (selective estrogen receptor modulator (SERM) or aromatase inhibitor (AI), with or without ovarian function suppression) with initial normal blood lipids were included for comparison study. Dyslipidemia was dened as abnormality of cholesterol/LDL/ HDL/triglyceride. Risk accumulation function was used to calculate the incidence of dyslipidemia to assess absolute risk, and the multivariate COX regression model was used to calculate the relative risk of dyslipidemia between groups. Irrespective of menopause, AIs treatment causes higher risk of TC/LDL-C dyslipidemia than SERM. [SD], 1.3 [0.7] mmol/L) (cid:0) HDL-C(mean [SD], 1.4 [0.4] mmol/L) (cid:0) LDL-C(mean [SD], 2.9 [0.9] mmol/L) 18 (cid:0) A prospective cohort study in Norway reported that the blood lipid levels of breast cancer patients at rst diagnosis were: TC(mean [SD], 5.82 [1.3] mmol/L) (cid:0) TG(mean [SD], 1.2 [0.8] mmol/L) and HDL-C(mean [SD], 1.8 [0.4] mmol/L) 19 . A study of 1054 newly diagnosed breast cancer patients in Chongqing, China showed that TC, mean [SD], 4.5 [0.9] mmol/L; TG, mean [SD], 1.3 [1.0] mmol/L; HDL-C, mean [SD], 1.4 [0.4] mmol/L; LDL-C, mean [SD], 2.8 [0.8] mmol/L) 20 . The baseline blood lipid levels of newly diagnosed early breast cancer patients in our study were similar to those in Chongqing, but better than those reported in Canada and Norway. Several studies have shown that compared with western countries, Chinese breast cancer patients are younger at initial diagnosis, with an average age of 45-55 21 and a lower BMI 22 , which leads to a lower baseline blood lipid level in Chinese breast cancer patients than those in western countries.


Introduction
Breast cancer is the most common malignant tumor in Chinese women 1 . Dyslipidemia, abnormal bone metabolism, mental anxiety and depression, as common concomitant diseases, are important contents of the full-course management of breast cancer 2 . Among them, dyslipidemia refers to the increase of serum cholesterol, TG or LDL-C, or the decrease of HDL-C 3 , while dyslipidemia is considered to be the main risk factor for ASCVD occurrence and development 4,5 . According to the epidemiological evidence in China, raised cholesterol is the most important and clear risk factor for ASCVD in China, while LDL-C rise is the third largest risk factor for cardiovascular disease death in China 6 . Cohort studies have found that cardiovascular death accounts for about 16.3% of the total deaths among breast cancer patients 7 . Compared with breast cancer patients without heart disease, breast cancer patients with heart disease have a 59% higher recurrence rate and a 60% higher mortality rate, and myocardial infarction can accelerate breast cancer progression and metastasis 8 . For breast cancer patients, it is very important to carry out blood lipid management in the early stage, in order to reduce the risk of heart disease.
Endocrine therapy is one of the standard treatments for estrogen receptor-positive breast cancer, which is mainly divided into selective estrogen receptor modulator (SERM) and aromatase inhibitor (AI) 9 . Different endocrine drugs may have different effects on blood lipid levels in patients with breast cancer. Previous clinical studies have shown that tamoxifen has good cardiovascular effects on postmenopausal breast cancer patients, including reducing total cholesterol and low-density lipoprotein cholesterol (LDL-C) levels, and increasing high-density lipoprotein cholesterol levels 10,11 . The ATAC trial compared the adverse reactions of anastrozole and tamoxifen in postmenopausal breast cancer patients, and the results of 100-month follow-up showed that the incidence of hypercholesterolemia in patients treated with anastrozole was signi cantly higher than that in patients treated with tamoxifen group 12 . Shien et.al found in a prospective clinical trial that TC and LDL-C levels at 12 and 24 months after toremifene treatment were higher than those in letrozole group 13 . A retrospective study found that in postmenopausal breast cancer patients, the abnormal level of triglyceride treated with letrozole for 24 months was higher than that of exemestane 14 .
Therefore, the monitoring of dyslipidemia is very important. However, the proportion of dyslipidemia in Chinese breast cancer patients at initial diagnosis, the impact of different endocrine therapy on blood lipid in Chinese breast cancer patients, especially for premenopausal breast cancer patients, are still lack of large-scale real-world research evidence. Based on the large cohort of breast cancer in West China Hospital of Sichuan University, we analyzed the proportion and distribution of baseline dyslipidemia in early breast cancer patients, and compared the effects of different endocrine therapies such as SERM and AI on blood lipid levels in premenopausal and postmenopausal women respectively.

West China Hospital Breast Cancer Cohort (WHC BC cohort)
Patients pathologically diagnosed with breast cancer are prospectively registered in the Breast Cancer Information Management System (BCIMS) at West China Hospital, Sichuan University since 2008 [15][16][17] . Medical records, diagnostic pathology reports, treatments records are recorded by oncologists. All patients are followed by outpatient visit or telephone at 3 to 4-month intervals within 3 years after diagnosis, 6-month intervals within 4-5 years, and then annually. The study was approved by the biomedical research ethics committee of West China Hospital (reference number: 20200427).

Study Design
Participants were breast cancer patients registered in BCIMS from October 6, 2008 to April 15, 2017. 1. EBC women data (See in Supplement Figure 1A) sets included:(1) Pathologically con rmed non-metastatic M0 female breast cancer patients;(2) At least one blood lipid test record within one month before diagnosis; Excluded: (1) No dyslipidemia diagnosis record at the time of diagnosis but taking hypolipidemic drugs;(2) Uncertain menstrual status. 2. EBC data sets with unchanging endocrine therapy (See in Supplement Figure 1B) included:(1) Pathologically con rmed non-metastatic M0 female breast cancer patients received standard endocrine therapy;(2) Blood lipid was detected within 3 months of endocrine therapy, and the level of blood lipid was normal; Excluded:(1) Dyslipidemia in the rst 3 months of endocrine therapy; (2) Uncertain menstrual status.

De nition of dyslipidemia
The blood lipid test data were obtained through the LIS system of West China Hospital of Sichuan University. According to the "2016 Chinese guideline for the management of dyslipidemia in adults" 3 ,1. Any of the following conditions is de ned as dyslipidemia, total cholesterol≥6.2 mmol/L, LDL≥4.1 mmol/L,HDL< 1.0 mmol/L or triglyceride≥2.3 mmol/L; 2. ASCVD high-risk levels: LDL≥ 4.9 mmol/L or total cholesterol ≥ 7.2 mmol/L. In the EBC women dataset, if the level of any blood lipid index of a breast cancer patient at the time of diagnosis (including one month before diagnosis) reaches the abnormal standard of "2016 Chinese guideline for the management of dyslipidemia in adults", it is de ned as an abnormality of this index and dyslipidemia. In the EBC women with endocrine therapy dataset, women with breast cancer who had normal blood lipid before endocrine therapy met the abnormal standard of "2016 Chinese guideline for the management of dyslipidemia in adults" during the 60-month follow-up period, which was de ned as abnormal of this index.

Data Analysis
Descriptive statistics were obtained for all study variables. Continuous variables are expressed as mean (SD) or median (interquartile range [IQR]) values. Categorical data are expressed as numbers (proportions). All categorical variables were compared for the study outcome by using the Fisher exact test or χ2 test, and continuous variables were compared using the t test or the Mann-Whitney U test, as appropriate. Multivariate logistic regression was used to nd the independent risk factors for dyslipidemia at baseline.
A Cumulative Incidence analysis and a log-rank test were used to access the cumulative incidence rates of dyslipidemia which was used to assess the absolute risk of dyslipidemia during 60 months for patients with different endocrine therapy. Pairwise comparison between multiple groups was carried by log-rank test, which p-value was adjusted by Benjamini-Hochberg procedure. Multivariate Cox regression models, involving variables with a p-value less than 0.05, were used to assess the relative risk for dyslipidemia among different group. We assessed the relative risk of dyslipidemia within 5 years among patients with different menopause status and endocrine therapy drugs. Data analysis and graph drawing are through R version 3. 6

Prevalence of Dyslipidemia and Risk Factors
At the initial diagnosis of EBC women data set, 978 cases (16.5%) had dyslipidemia, and 75 / 978 cases (7.7%) reached the high-risk blood lipid level of ASCVD. As shown in Table 2, the prevalence of dyslipidemia in the higher age group was higher than that in the lower age group (P < 0.001). The prevalence of dyslipidemia in each age group was 18-34 years old (6.4%), 35-44 years old (9.7%), 45-54 years old (16.7%), 55-64 years old (26.3%) and 65 years old 28.7% . The proportion of blood lipid reaching the high level of ASCVD was also statistically signi cant between age groups (P = 0.012). The proportion of dyslipidemia was also different between different BMI groups (P<0.001), and the proportion of dyslipidemia in Obese group (22.9%) or Overweight group (28.3%) was higher than that in low BMI (8.3%) or normal BMI group (12.9%). The abnormal proportion of blood lipids in menopausal patients (25.7%) was higher than that in non-menopausal patients (10.9%), and there was a similar trend for blood lipids to reach the high-risk level of ASCVD (menopause (10.0%) vs non-menopause (4.2%), P = 0.001). There was no signi cant difference in the prevalence of dyslipidemia among Subtypes, Stage and each hormone receptor group (ER, PR, Her2 and Ki67).
Age, BMI, menopause status, stage, ER, PR, HER2, Ki67 were included to construct binary multivariate logistic regression model. As shown in Figure 1, the risk of dyslipidemia was increased in both Overweight and Obese group compared with low BMI levels Odds ratio [ Figure 1).

Abnormalities in Four Blood Lipid Indexes among Premenopause EBC
We further analyzed the effect of speci c endocrine therapy on the incidence of single index of dyslipidemia. The non-menopausal group received three types of endocrine therapy modes: SERM (77.9% , OFS+AI(15.0%), OFS+SERM(7.1%).The speci c plans were: TAM 74.7% and TOR 3.2% OFS+TAM 6.9% and OFS+TOR(0.2%) OFS+ANA 7.7% OFS+LET 5.3% OFS+EXE 2.0% . Before endocrine therapy, the blood lipid levels were TC Pairwise log-rank test showed that compared with SERM group, the 1-year abnormal incidence of TC and LDL-C in OFS + AI Group was signi cantly higher TC: OFS+AI vs SERM, 22% vs 3.5%, P<0.001; LDL-C: OFS+AI vs SERM, 12.2% vs 1.4% , P<0.001; Supplement Table 2 and   Supplement Table 4 ;the 5-year abnormal incidence of TC and LDL-C in OFS + AI Group was also signi cantly higher TC: OFS+AI vs SERM, 22.0% vs 3.5%, P<0.001; LDL-C: OFS+AI vs SERM, 12.2% vs 1.4% , P<0.001; Supplement Table 2 and Supplement Table 4 . In the subgroup analysis of speci c drugs, we found that compared with TAM group, the 5-year incidence of TC and LDL-C in OFS+ANA or OFS+LET was signi cantly increased, and the difference between OFS + ANA and OFS + LET was not signi cant Supplement Table 2 and Supplement Table 6 . In order to determine the relative risk of different treatment modes or drugs in the occurrence of TC abnormality and LDL-C abnormality, we constructed a multivariate COX regression model, the factors with signi cant single factor COX regression P value between the corresponding groups were included for correction, and it was found that the OFS + AI group had a higher risk of LDL-C abnormality than the SERM group ( 3.37] mmol/L . Similar to the premenopausal group, there were signi cant differences in the risk of abnormal TC and LDL-C between SERM therapy and AI therapy TC: P<0.001, LDL-C: P=0.002 Figure 3 . The incidence of 1-year abnormal TC in AI group was higher than that in SERM group AI vs SERM, 13.9% vs 4.5%, P=0.002; Supplement Table 3 and  Supplement Table 5 , and the incidence of abnormal TC in 5 years was also higher than that in SERM group AI vs SERM, 21.9% vs 8.2%, P<0.001; Supplement Table 3 and Supplement Table 5 . Compared with SERM group, the 1-year incidence of abnormal LDL-C in AI group did not increase signi cantly AI vs SERM, 8.6% vs 2.5%, P=0.095 , but the 5-year abnormal risk increased signi cantly AI vs SERM, 13.3% vs 2.5%, P=0.002; Supplement Table 3 and Supplement Table 5 . Similarly, in the subgroup analysis of speci c drugs, we found the same trend as premenopausal : the incidence of abnormal TC and LDL-C in 1 year and 5 years of OFS + ANA or OFS + LET was signi cantly higher than that in TAM group, and the difference between OFS + ANA and OFS + LET was not signi cant Supplement Table 3 and Supplement

Discussion
This study is currently the largest single-center breast cancer blood lipid cohort study in China. This study found that 16.6% of patients with early breast cancer had dyslipidemia at the time of rst diagnosis, and older age, high BMI levels and menopause were all independent risk factors for dyslipidemia. In EBC patients receiving endocrine therapy, the risk of dyslipidemia in menopausal patients was still higher than that of nonmenopausal patients. For the premenopausal group, the risk of abnormal TC and LDL-C in 1 year or 5 years in OFS + AI Group was signi cantly higher than that in SERM group. For postmenopausal patients, the 1-year or 5-year risk of abnormal TC in AI group was signi cantly higher than that in SERM group, and the 5-year risk of abnormal LDL-C in AI group was signi cantly higher than that in SERM group.  20 . The baseline blood lipid levels of newly diagnosed early breast cancer patients in our study were similar to those in Chongqing, but better than those reported in Canada and Norway. Several studies have shown that compared with western countries, Chinese breast cancer patients are younger at initial diagnosis, with an average age of 45-55 21 and a lower BMI 22 , which leads to a lower baseline blood lipid level in Chinese breast cancer patients than those in western countries.
At present, there is little evidence about the risk factors of dyslipidemia in breast cancer patients. Li et al. conducted a sample survey of 5375 people in Chongqing, China, and found that high BMI and high age were independent risk factors for female dyslipidemia 23 . Several epidemiological studies showed that the level of dyslipidemia in postmenopausal women was signi cantly higher than that in premenopausal women 24 . This study con rmed that high age, high BMI level and menopause are independent risk factors for dyslipidemia in women with early breast cancer, which is consistent with the above research results. Therefore, whether premenopausal or postmenopausal, physicians should pay attention to their dyslipidemia, especially for people undergoing endocrine therapy after menopause, which will help to monitor the occurrence of cardiovascular events.
In China, the full-course management of breast cancer and its associated diseases is receiving more and more attention 2 . However, the occurrence time and incidence of dyslipidemia in hormone positive EBC patients, especially in premenopausal patients after receiving different endocrine therapy are still not clear. This study found that after endocrine therapy, the incidence of dyslipidemia in 5 years of menopausal patients is higher than that of non-menopausal patients, just like the incidence of dyslipidemia in 1 year, with the incidence of 42.6% and 32.6% in menopausal and non-menopausal patients respectively. The risk of abnormal TC and LDL-C in premenopausal breast cancer patients in one or ve years showed a trend: OFS + AI Group was signi cantly higher than SERM group, OFS + LET or OFS + ANA group was signi cantly higher than TAM group. While for postmenopausal EBC women, the risk of abnormal TC and LDL-C was also higher in AI group than that in SERM group, which was consistent with the clinical reports of early hormonal receptor-positive BC in endocrine therapy 13,25−27 . This suggests that more than one third of premenopausal and postmenopausal women with breast cancer may have dyslipidemia after long-term endocrine therapy, and SERM is more likely to cause the changes of TC and LDL-C than AI, which are the two important risk factors of cardiovascular disease. This study has some limitations. The research object of this study comes from the single-center cohort of West China Hospital of Sichuan University in Western China, which does not represent the total population of China. This study focused on the incidence of dyslipidemia, and did not further explore the incidence of ASCVD and cardiovascular disease.

Conclusion
This study is based on the analysis of a large-sample breast cancer cohort in China, and found that 16.6% of early breast cancer patients in China had dyslipidemia at the time of diagnosis. Older age, high BMI and menopause were risk factors for dyslipidemia. Among the hormone receptorpositive EBCs with normal blood lipids, dyslipidemia occurred in about 1 / 3 of the patients within 5 years after receiving endocrine therapy, and the dyslipidemia rate of menopausal patients was higher than that of non-menopausal patients in the rst year. The incidence of TC and LDL-C abnormalities after AI treatment was higher than that in SERM group in menopausal and non-menopausal patients. This suggests that dyslipidemia is one of the most common concomitant diseases of breast cancer. When physicians make endocrine decisions, they need to consider that AI is more likely to cause abnormal TC and LDL-C than SERM, and these two indicators are risk factors of cardiovascular disease.
For patients who have received endocrine therapy, whether premenopausal or postmenopausal, dyslipidemia is very common and must be closely detected. This study provides important clinical data for the full-course management strategy of breast cancer hyperlipidemia.

Declarations
Ethics approval and consent to participate: The study was conducted in accordance with the principles of the Declaration of Helsinki. This study was also approved by the biomedical research ethics committee of West China Hospital (reference number: 20200427).

Not applicable
Availability of data and materials The data are available for all study authors. The datasets used and analysed during the current study are available from the corresponding author on reasonable request.

Figure 2
Cumulative abnormal TC and LDL-C incidence among early breast cancer pre-menopause patients for different endocrine therapy Cumulative curves showing TC (A and C) and LDL-C (B and D) dyslipidemia incidence. P values were obtained from log-rank tests for comparisons of abnormal TC and LDL-C incidence between different endocrine therapy groups. SERM, selective estrogen receptor modulator; TAM, tamoxifen; TOR, Toremifene; AI, aromatase inhibitor; ANA, Anastrozole; LET, Letrozole; EXE, Exemestane; OFS, ovarian function suppression; TC, Total cholesterol; TG, Triglyceride; HDL-C, HDL cholesterol; LDL-C, LDL cholesterol.

Figure 3
Cumulative abnormal TC and LDL-C incidence among early breast cancer menopause patients for different endocrine therapy Cumulative curves showing TC (A and C) and LDL-C (B and D) dyslipidemia incidence. P values were obtained from log-rank tests for comparisons of abnormal TC and LDL-C incidence between different endocrine therapy groups.S ERM, selective estrogen receptor modulator; TAM, tamoxifen; TOR, Toremifene; AI, aromatase inhibitor; ANA, Anastrozole; LET, Letrozole; EXE, Exemestane; TC, Total cholesterol; TG, Triglyceride; HDL-C, HDL cholesterol; LDL-C, LDL cholesterol.

Supplementary Files
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