Clinical characteristics and disease outcomes in ER+ breast cancer: a comparison between HER2+ patients treated with trastuzumab and HER2- patients

Background Trastuzumab has changed the prognosis of HER2+ breast cancer. We aimed to investigate the prognosis of ER+/HER2+ patients treated with trastuzumab, thus to guide escalation endocrine treatment in ER+ breast cancer. Methods ER-positive early breast cancer patients operated at Ruijin Hospital between Jan. 2009 and Dec. 2017 were retrospectively included. Eligible patients were grouped as HER2-negative (HER2-neg) or HER2-positive with trastuzumab treatment (HER2-pos-T). Kaplan-Meier analysis and Cox proportional hazards model were used to compare the disease-free survival (DFS) and overall survival (OS) between these two groups. Results A total of 3761 patients were enrolled: 3313 in the HER2-neg group and 448 in the HER2-pos-T group. Patients in the HER2-pos-T group were associated with pre/peri-menopause, higher histological grade, LVI, higher Ki-67 level, lower ER and PR levels (all P <  0.05). At a median follow-up of 62 months, 443 DFS events and 191 deaths were observed. The estimated 5-year DFS rate was 89.7% in the HER2-neg group and 90.2% in the HER2-pos-T group (P = 0.185), respectively. Multivariable analysis demonstrated that patients in the HER2-pos-T group had a better DFS than patients in the HER2-neg group (HR 0.52, 95% CI: 0.37–0.73, P <  0.001). The estimated 5-year OS rates were 96.0% and 96.3% in the two groups, respectively (P = 0.133). Multivariate analysis found that HER2-pos-T group was still associated with significantly better OS compared with the HER2-neg group (HR 0.38, 95% CI: 0.22–0.67, P = 0.037). Conclusion ER+/HER2+ breast cancer patients treated with trastuzumab were associated with superior outcome compared with ER+/HER2- patients, indicating HER2-positivity itself may not be an adverse factor for ER+ patients in the era of trastuzumab. Supplementary Information The online version contains supplementary material available at 10.1186/s12885-021-08555-4.


Introduction
Breast cancer is the most common cancer and the leading cause of death in women. More than 2,088,849 new cases of breast cancer were estimated worldwide in 2018 [1]. Breast cancer can be categorized into at least four subtypes based on the status of molecular markers for estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor 2 (HER2) [2].
About 15-20% of patients with breast cancer have HER2-amplfied and/or overexpressed tumors and about half HER2+ tumors express hormone receptor (HR) [3]. Previous reports showed that HER2 positivity was associated with a worse prognosis before the ear of anti-HER2 therapy [4][5][6]. In view of that, clinicians tended to recommend escalation endocrine therapy for patients with HR+/HER2+ disease, such as ovarian function suppression (OFS) in pre-menopausal women.
Clinical trials have demonstrated that addition of trastuzumab to standard chemotherapy in patients with HER2+ early-stage breast cancer significantly improved disease outcome [7][8][9][10][11], which was not influenced by HR status. Then, should ER+/HER2+ still be considered as an indicator of poor prognosis in the era of anti-HER2 treatment? In current study, we aimed to investigate the prognosis of ER+/HER2+ breast cancer patients treated with trastuzumab compared with ER+/HER2patients, thus to guide us to select appropriate endocrine treatment decision making.

Patient
Women who underwent surgery at General Surgery Department, Comprehensive Breast Health Center, Ruijin Hospital, Shanghai Jiaotong University School of Medicine from January 2009 to December 2017 were retrospectively enrolled. Clinicopathological, treatment, and follow up information were retrieved from Shanghai Jiaotong University Breast Cancer Database (SJTU-BCDB). Patients who met the following criteria were enrolled for further analysis: (1) female gender, (2) invasive breast cancer, (3) no history of prior malignancy, (4) no evidence of distant metastasis at diagnosis, (5) ER+/ HER2-breast cancer or ER+/HER2+ tumors treated with trastuzumab, and (6) complete clinical and follow-up data. Those who were diagnosed with ER+/HER2+ breast cancer but received no trastuzumab treatment were excluded. This study was reviewed and approved by the independent Ethical Committees of Ruijin Hospital, Shanghai Jiao Tong University School of Medicine.

Histopathological assessments
Tumor histo-pathologic assessment was conducted by Department of Pathology, Ruijin Hospital, Shanghai Jiaotong University School of Medicine. The methods and criteria for immunohistochemistry (IHC) assessment of ER, PR, HER2 and Ki-67 were as described in our previous reports [12,13]. The cutoff value for ER positivity and PR positivity was at least 1% positive tumor cells with nuclear staining [14]. HER2 status was evaluated semi-quantitatively by IHC according to the ASCO/CAP guidelines [15][16][17]. Tumors with IHC HER2 2+ were further examined by fluorescence in situ hybridization (FISH), and HER2 positivity was defined as IHC HER2 3+ or FISH +. Ki-67 expression was scored as the percentage of positive invasive tumor cells with any nuclear staining and recorded as mean percentage of positive cells.

Follow-up
All patients were followed up by outpatient visit or call every 3 months for the first 2 years after surgery, every 6 months between the 3rd and 5th years, then annually until death. Disease-free survival (DFS) was computed from the date of surgery to the date of the following events: locoregional recurrence, contralateral breast cancer, secondary non-breast malignancy, distant recurrence at any site, and death of any cause. Overall survival (OS) was defined as the time period from the date of surgery to the date of death of any cause. Diagnosis of recurrence or metastasis was generally based on patient's radiographic images and/or pathological biopsies when accessible. Last follow-up was conducted in April 2021.

Statistical analysis
Descriptive characteristics of categorical variables were tested using chi-square test or Fisher's exact test. Multivariate logistic regression analysis was used to compare the baseline clinic-pathological features and therapies between these two groups. The estimated 5-year DFS and OS were calculated by Kaplan-Meier analysis. Cox proportional hazards regression analysis was performed to calculate independent prognostic factors in ER+/ HER2+ patients treated with Trastuzumab. All statistical procedures were performed using SPSS software, version 22.0 (SPSS Company, Chicago, IL). P < 0.05 was considered statistically significant.

Prognostic effect of HER2 status in ER+ patients according to different subtypes
Prognostic effect interactions were not significantly different between HER2 status and certain subgroups including age, menstrual status, tumor size, ALN status, tumor grade, ER level, PR level, and Ki-67 level (Supplementary Fig. S1).

Predictive effect of HER2 status in ER+ patients
There were 256 pre-menopausal women in the present cohort who were treated with OFS (75 with SERM, 16 with SERM-AI, and 165 with AI), and 1211 received endocrine therapy alone (Supplementary Table S2). The rate of OFS utilization was higher in the HER2-pos-T group than that in the HER2-neg group (23.3% vs. 16.5%, P = 0.016). For HER2-patients, 86.5% in the OFS arm and 92.2% in the Non-OFS arm were disease-free at 5 year (P = 0.013, Supplementary Fig. S4a). While the 5year DFS rate was 89.5% in the OFS arm and 90.2% in the Non-OFS arm among HER2+ patients (P = 0.995, Supplementary Fig. S4b). There was no interaction between HER2 status and OFS benefit in terms of DFS (P = 0.556). For HER2-patients, 97.8% in the OFS arm and 98.0% in the Non-OFS arm were alive at 5 year (P = 0.245, Supplementary Fig. S4c). The rates among HER2+ patients were 100.0% and 96.3%, respectively (P = 0.277, Supplementary Fig. S4d). Similarly, no interaction between HER2 status and OFS benefit in OS were observed (P = 0.965).

Discussion
Patients with ER+/HER2+ breast cancer had a worse prognosis compared to those with ER+/HER2-disease in the pre-trastuzumab treatment era, who were more frequently treated with chemotherapy and escalation endocrine therapy. Consistent with previous studies, our current study found that ER+/HER2+ tumors were associated with pre/ peri-menopause, higher histological grade, LVI, higher Ki-67 level, lower ER and PR levels. After adjusting for these characteristics, the DFS and OS rates were significantly better for ER+/HER2+ patients treated with trastuzumab than those with ER+/HER2-tumor, indicating HER2positivity itself may not be an adverse factor for ER+ patients if they were treated with trastuzumab, which may guide further clinical treatment decision making. Previous reports validated that ER+/HER2+ breast cancers were associated with more unfavorable clinical features compared with ER+/HER2-diseases. A study Fig. 3 Kaplan-Meier estimates of DFS and OS for pre/peri-menopausal patients (a and b) and post-menopausal patients (c and d). a. The estimated 5-year DFS rate was 90.3% for HER2-patients and 89.6% for HER2+ patients treated with trastuzumab (P = 0.422). HER2-pos-T was associated with significantly better DFS in multivariate analysis (P = 0.013). b. The estimated 5-year OS rate was 97.4% in the HER2-neg group and 96.7% in the HER2-pos-T group (P = 0.557). No difference was observed between these two groups in multivariate analysis (P = 0.080). c. The estimated 5-year DFS rate was 89.3% for HER2-patients and 90.7% for HER2+ patients treated with trastuzumab (P = 0.292). HER2-pos-T was associated with significantly better DFS in multivariate analysis (P = 0.005). d. The estimated 5-year OS rate was 95.0% in the HER2-neg group and 96.0% in the HER2-pos-T group (P = 0.249). HER2-pos-T was associated with significantly better OS in multivariate analysis (P = 0.008)  To the best of our knowledge, this is the first study comparing the prognosis of ER+/HER2+ patients treated with trastuzumab and those patients with ER+/HER2-tumors. Previously, two trials that assessed the efficacy of trastuzumab prospectively included a parallel observational cohort in which women with HER2-diseases received the same chemotherapy as did the HER2+ group. The 3-year results of the FinHer study indicated that survival free of distant disease was comparable among women with HER2+ cancer who received trastuzumab and those with HER2-cancer (HR 1.09, 95% CI 0.52-2.29, P = 0.82) [20]. In the NOAH trial, the estimated 5-year rate of event-free survival was 58% in the HER2+ treated with trastuzumab group and 61% in the HER2-group [21]. However, because of the differences in clinic-pathological factors between HER2+ patients and those with HER2-tumors, the actual efficacy of trastuzumab on prognosis remained unknown. In the present study, ER+/HER2+ patients treated with trastuzumab had significantly better 5-year DFS (HR 0.52, 95% CI: 0.37-0.73, P < 0.001) and OS (HR 0.38, 95% CI: 0.22-0.67, P = 0.037) rates than those with ER+/HER2-tumor in multivariable analysis by adjusting clinicopathological factors, indicating HER2 positivity was no longer an adverse factor for ER+ patients if they were treated with trastuzumab, which may guide further clinical treatment decision making.
For pre-menopausal patients with high risk factors, adding OFS with endocrine therapy was recommended according to the SOFT and TEXT trials [22][23][24][25][26][27]. Several clinical trials showed heterogeneity of OFS treatment benefit according to HER2 status [23][24][25][26][27]. Data from the SOFT trial suggested that HER2+ patients received a greater DFS benefit from the addition of OFS to tamoxifen compared with HER2-patients (HR 0.41 vs. 0.83, interaction P = 0.04) [26]. However, the joint analysis of SOFT and TEXT showed that more treatment benefit with exemestane plus OFS than tamoxifen plus OFS was found in patients with HER2-cancers (interaction P = 0.014) [26]. Similarly, a statistically significant treatment benefit difference according to the HER2 status was found in the HOBOE trial and OFS plus letrozole was more effective compared with OFS plus tamoxifen in the HER2-patients [25]. In the SOFT and TEXT trials, 60.1% ER+/HER2+ patients received anti-HER2 therapy. In our study, all ER+/HER2+ patients were treated with trastuzumab and they had significantly better disease outcome compared with HER2-patients, suggesting that only HER2 positivity itself may not be enough to recommend additional OFS treatment in pre-menopausal ER+/HER2+ patients if they were treated with trastuzumab.
In the present study, we observed a higher utilization rate of OFS among ER+/HER2+ patients treated with trastuzumab than ER+/HER2-patients. However, HER2 status seemed to provide no predictive information for OFS benefit with the presence of trastuzumab treatment. These results also suggested that HER2 positivity itself might not necessarily be an indicator for escalation endocrine therapy, which needed further research.
There were several potential limitations in this study. First, the study was retrospective and single-centered, which may lead to unavoidable bias in basic characteristics and treatment patterns between different arms. For example, 99.6% of the patients in the HER2-pos-T group received chemotherapy, whereas the percentage of chemotherapy was 55.6% in the HER2-neg group. Secondly, 136 ER+/HER2+ patients who didn't receive trastuzumab (small tumor or patients reject to receive treatment) were excluded from the analysis. Moreover, the follow-up was still too short to clarify the effect of trastuzumab on disease outcomes, especially for ER+ disease, which needed additional follow-up. members and breast cancer specialized nurses for their great assistance in this study.
Authors' contributions XSC and KWS carried out the study conception and design. SL performed the data analysis, study interpretation and draft the manuscript. XSC reviewed and revised the manuscript. JYW, OH, JRH, LZ, WGC, YFL, XSC and KWS participated in data collection. All authors read and approved the final manuscript.

Funding
This study was funded by the National Natural Science Foundation of China (Grant Number: 81772797). Shanghai Municipal Education Commission-Gaofeng Clinical Medicine Grant Support (20172007); Ruijin Hospital, Shanghai Jiao Tong University School of Medicine-"Guangci Excellent Youth Training Program" (GCQN-2017-A18). All these financial sponsors had no role in the study design, data collection, analysis or interpretation.

Availability of data and materials
The datasets used and/or analysed during the current study are available from the corresponding author on reasonable request.

Declarations
Ethics approval and consent to participate This article does not contain any studies with human participants performed by any of the authors. All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards. This study was reviewed and approved by the independent Ethical Committees of Ruijin Hospital, Shanghai Jiao Tong University School of Medicine. Informed consent was obtained from all participants or, if participants are under 18, from a parent and/or legal guardian.

Consent for publication
Not applicable.