Efficacy and safety of neoadjuvant treatment of trastuzumab and pyrotinib plus dalpiciclib in HR-negative/HER2-positive breast cancer: an exploratory, open-label phase II study

Abstract

Background:

To evaluate the efficacy and safety of a chemotherapy-free regimen consisting of monoclonal antibody trastuzumab, tyrosine kinase inhibitor pyrotinib, and CDK4/6 inhibitor dalpiciclib in patients with hormone receptor-negative/HER2-positive (HR-HER2+) early breast cancer (EBC).

Materials and Methods:

This open-label, single-arm, phase II study was designed using the Simon two-stage method (Registration Number: Chi-CTR-2200060748). Patients with operable HR-HER2+ EBC (T1-3 and N0–2) were enrolled. Eligible patients received trastuzumab (HLX02, 8 mg/kg loading dose, followed by 6 mg/kg every 3 weeks intravenously), pyrotinib (400 mg daily orally), and dalpiciclib (125 mg daily orally for 3 weeks, followed by 1 week off) for 16 weeks. Surgery was performed 3–6 weeks after the completion of drug treatment. The primary endpoint was total pathological complete response (tpCR, ypT0/Tis, and ypN0) rates at surgery, and secondary endpoints included breast pCR (bpCR) rates (ypT0/Tis), residual cancer burden (RCB), objective response rate (ORR), change of Ki-67 scores, survival, and safety.

Results:

Between June 2022 and June 2024, a total of 34 patients with a median age of 55 years (range: 35–67) were enrolled. Thirty patients received all cycles of treatment and underwent surgery with a median follow-up of 20 months. The tpCR was achieved in 19 patients (63.3%; 95% CI, 45.5–78.1%). The bpCR was 66.7% (20/30). The number of patients with RCB-0 or RCB-I was 22 (73.3%). The most common Grade 3 treatment-related adverse events were diarrhea (50.0%), neutropenia (20.6%), and leukopenia (17.7%). No Grade 4 events or treatment-related deaths occurred.

Conclusion:

In patients with HR-HER2+ EBC, the neoadjuvant therapy with trastuzumab, pyrotinib, and dalpiciclib has promising activity and manageable toxicity. Further investigation is needed.

HIGHLIGHTS

• The therapy of trastuzumab, pyrotinib, and dalpiciclib is a new approach for breast cancer. The therapy for HR-HER2+ breast cancer has promising activity in the neoadjuvant setting. The therapy has manageable toxicity.

Introduction

Human epidermal growth factor receptor 2 (HER2)-positive breast cancer is an aggressive subtype, accounting for 15−20% of all cases. Around 30% of HER2-positive (HER2+) breast cancers do not express hormone receptor (HR) which includes estrogen receptor (ER) and progesterone receptor (PR), and this subtype of breast cancer is with high levels of HER2 mRNA and protein expression compared with HR-positive HER2-positive (HR+ HER2+) breast cancers[1].

Significant progress in survival has been made with the help of HER2-targeted therapy^[2,3]. Traditional treatments often combine chemotherapy and HER2-targeted therapy, but the side effects of chemotherapy seriously affect patients’ quality of life. In recent years, the use of chemotherapy-free regimens in the treatment of HER2+ disease has attracted widespread attention, especially in neoadjuvant therapy. The pathological complete response rate (pCR) of using trastuzumab and pertuzumab without chemotherapy in patients with HR-negative HER2-positive (HR-HER2+) breast cancer reached 27.3% in the NEOSPHERE trial and 34.3% in the ADAPT trial^[4,5]. In the TBCRC 006 study, the pCR rate of neoadjuvant lapatinib and trastuzumab was 36% in patients with HR-HER2+ breast cancer[6]. In the TBCRC 023 study, patients with HR-HER2+ breast cancer receiving 12-week or 24-week lapatinib and trastuzumab had a pCR of 18% or 20% with minimal side effects[7]. However, the efficacy of this dual HER2-targeted therapy is still unsatisfactory compared with the traditional treatments, which include chemotherapy and HER2-targeted therapy.

The application of CDK4/6 inhibitors in patients with HER2+ breast cancer has been gradually explored. Preclinical studies have confirmed that CDK4/6 inhibitors can cooperate with anti-HER2 therapy to effectively inhibit the growth and invasion of HER2+ breast cancer cells^[8–10]. Goel et al and Ciruelos et al have conducted phase I/II trials and evaluated the combination of CDK4/6 inhibitor and trastuzumab in HER2+ advanced breast cancer, but with limited activity^[11,12]. In an analysis of data from the phase III MONALEESA-2, MONALEESA-3, and MONALEESA-7 trials, the intrinsic HER2-enriched subtype of breast cancer exhibited a progression-free survival (PFS) benefit from ribociclib[13]. In the monarcHER trial, the combined regimens of abemaciclib and trastuzumab and fulvestrant significantly improved PFS versus chemotherapy plus trastuzumab in patients with HR+HER2+ advanced breast cancer[14]. In another study, patients with HER2+ metastatic breast cancer received the treatments of CDK4/6 inhibitor dalpiciclib and tyrosine kinase inhibitor pyrotinib, and the objective response rate was 70% regardless of HR status[15]. All these types of evidence suggest that CDK4/6 inhibitors may synergize with HER2-targeted drugs to suppress HER2+ breast cancer. However, the combination of monoclonal antibody, tyrosine kinase inhibitor, and CDK4/6 inhibitor for HER2+ breast cancer in the neoadjuvant setting is rare.

Here, we conducted the Xiangya Breast Cancer 01 (XYBC-01) study to investigate the efficacy and safety of neoadjuvant therapy with monoclonal antibody trastuzumab, tyrosine kinase inhibitor pyrotinib, and CDK4/6 inhibitor dalpiciclib in patients with HR-HER2+ breast cancer.

Methods

Study design and patients

This open-label, single-arm, phase II study was designed using the Simon two-stage method (Registration Number: Chi-CTR-2200060748). Eligible patients were treatment-naive women aged 18–70 years with pathologically confirmed HR-HER2+, early breast cancer (tumor stage T1–T3 and nodal stage N0–2). Tumors had to be HER2 immunohistochemistry (IHC) 3+ or 2+ and positive for fluorescence or chromogenic in situ hybridization, and be ER- and PR-negative (<1% of tumor cells expressing ER and PR by IHC). Other main inclusion criteria included Eastern Cooperative Oncology Group performance status of 0 or 1 and adequate hepatic, renal, bone marrow, and cardiac function based on laboratory assessments. Key exclusion criteria included metastatic disease (stage IV), inflammatory breast cancer, other malignancies, prior anti-cancer therapy or radiotherapy for any malignancy (except cured cervical carcinoma in situ, basal cell carcinoma, or squamous cell carcinoma), impaired cardiac function, uncontrolled hypertension, pregnancy, and refusal to use contraception.

The study was conducted in accordance with the Declaration of Helsinki and Good Clinical Practice guidelines. The study protocol was reviewed and approved by the ethics committee of Xiangya Hospital of Central South University. Written informed consent was obtained from each patient before enrollment.

Treatment

Eligible patients received oral pyrotinib (400 mg once daily) and dalpiciclib (125 mg once daily on days 1–21, every 28 days) for 16 weeks. Intravenous trastuzumab (HLX02, 8 mg/kg loading dose followed by 6 mg/kg maintenance dose) was administered once every 21 days for six cycles. Dalpiciclib was allowed to be used even if Grade 3 AE of neutropenia and leukopenia occurred. Because of diarrhea, dose delay and reduction of pyrotinib were permitted for the management of Grade 3 AEs. A dose delay for pyrotinib of more than 7 days in each cycle was not permitted. After the enrollment of 13 patients, the initial dose of pyrotinib was adjusted to 320 mg because of poor tolerance evidenced by the high incidence of diarrhea and vomiting. A dose reduction for pyrotinib of less than 240 mg was not allowed. The preventive and therapeutic use of SMECTA or loperamide was allowed. Surgery was performed 3–6 weeks after the completion of the last cycle of trastuzumab. All this work has been reported in line with the STROCSS criteria^[16,17].

Study end points

The primary endpoint was tpCR rates (ypT0/Tis, ypN0). The tpCR was defined as the disappearance of all invasive tumors in the breast and axillary lymph nodes. The secondary endpoints included breast pCR (bpCR) rates (ypT0/Tis, defined as no invasive tumors in the breast), residual cancer burden (RCB), objective response rate (ORR, defined as the proportion of patients who had a best overall response of complete or partial response during neoadjuvant therapy), event-free survival (EFS, defined as the time from enrollment to the first documentation of progressive disease while on study therapy, postoperative disease recurrence, or death from any cause), changes in Ki-67 scores, and safety.

Assessments

Pathological response was assessed by two local pathologists back-to-back using tumor tissue resection specimens obtained at surgery. RCB was categorized as RCB-0, RCB-I, RCBII, and RCB-III according to the assessment system proposed by the MD Anderson Cancer Center online software Residual Cancer Burden Calculator. In short, the online software includes the parameters of primary tumor bed area, overall cancer cellularity (as a percentage of area), percentage of cancer that is in situ disease, number of positive lymph nodes, and diameter of the largest metastasis. Ki-67 data were obtained from the department of pathology and were assessed by IHC. We did physical examinations before every cycle of trastuzumab. The MRI assessment of involved lesions at baseline and before surgery was done for every patient, and it was suggested after administration of three cycles of trastuzumab. Objective responses were assessed by investigators according to the Response Evaluation Criteria in Solid Tumors, version 1.1. AEs were monitored from the initiation of neoadjuvant therapy until 28 days after the last dose of neoadjuvant therapy according to the National Cancer Institute Common Terminology Criteria for Adverse Events, version 5.0. Blood routine, blood biochemistry, and urine routines were done at baseline, before administration of every cycle of trastuzumab, and before surgery. The electrocardiogram and heart function test were performed before each cycle of trastuzumab and surgery.

Statistical analysis

We used Simon’s two-stage design. The null hypothesis of a tpCR rate of 20% was adopted for the chemotherapy-free neoadjuvant regimen of dual HER2 blockade. Assuming a tpCR rate of 42% would be achieved following neoadjuvant trastuzumab and pyrotinib plus dalpiciclib, a total of 34 patients (including 13 in the first stage) were required when considering a one-sided α of 5%, a power of 80%, and a dropout rate of 10%. If at least 3 of 13 evaluable patients achieved a tpCR in the first stage, the trial would proceed to the next stage, and recruitment would be continued until a total of 34 patients were enrolled. The treatment would be considered promising if 9 or more out of 30 evaluable patients achieved a tpCR. Statistical analyses were performed using SAS version 9.4 software (SAS Institute Inc.) and PASS version 15.0.3 software (NSCC, LLC, Kaysville, UT, USA).

Results

Patient characteristics

Between 24 June 2022 and 20 June 2024, a total of 45 patients were screened for eligibility, and 34 patients signed the informed consent form and received at least one cycle of trastuzumab (Fig. 1). Among the 34 patients, 30 finished the whole treatment cycles and received surgery of modified radical mastectomy or breast-conserving surgery, and one patient withdrew informed consent and insisted on undergoing surgery after administration of the first cycle of trastuzumab. Another patient withdrew informed consent and refused to receive any therapies after the first cycle of trastuzumab. Two patients dropped out after receiving the whole cycles of drug treatment and refused surgical treatment because of no palpable tumor in the breast; thus, 34 patients were included in the safety population. Baseline characteristics are shown in Table 1. The median age was 55 years (range, 35–67). Twenty-four patients had stage II disease, and 10 patients had stage III disease. Nineteen patients had enlarged lymph nodes. Thirty patients had a Ki-67 score of ≥20%.

Figure 1.

Trial profile. Treatment summary and data collection of study participants.

Table 1.

Baseline characteristics

Characteristics	Patients (n = 34)
Median age, years (range)	55 (35–67)
<55	17
≥55	17
Menopausal status
Premenopausal or perimenopausal	11
Postmenopausal	23
Stage at baseline
II	24
III	10
Tumor size at baseline
cT1	2
cT2	25
cT3	7
Nodal status at baseline
cN0	15
cN1–2	19
Ki-67 level
<20%	4
≥20%	30
HER2 status
IHC 2+ and FISH (+)	4
IHC 3 +	30

Efficacy and survival

In the first stage, with the initial dosing of pyrotinib 400 mg, 9 of 13 evaluable patients achieved tpCR, allowing the study to proceed to the second stage. There were 9 (69.2%) patients reducing their dose to 320 mg or 240 mg and 7 (53.8%) patients experiencing dose delays in the first stage as shown in Table 2. In the second stage with the initial dosing of pyrotinib 320 mg, 10 of 17 patients achieved tpCR, 3 (17.6%) patients had dose reduction, and 9 patients underwent dose delays (Table 2). Overall, tpCR was achieved in 19 of 30 patients (63.3%; 95% CI, 45.5–78.1%). The tpCR rate was 65.0% for patients with stage II disease and 60.0% for stage III. The tpCR rates of cN1–2 and cN0 patients were 63.2% and 63.6%. The bpCR rate was 66.7% for the cohort of patients, 65.0% for patients with stage II disease, and 70.0% for those with stage III. None of the four patients with the tumor of HER2 IHC 2+ achieved tpCR or bpCR. A subgroup analysis showed there was a trend that tpCR would be higher in patients with HER2 3+ (73.1%, 95% CI, 52.2–88.4%) by IHC than those with HER2 2+ (0, 95% CI, 0–60.2%) (Fig. 2). The number of patients with RCB-0 or RCB-I was 22 (73.3%), and patients with RCB-II or RCB-III were 4 (13.3%). Among these 30 patients with evaluable response, 26 achieved partial response and 4 had stable disease, resulting in an ORR of 86.7% (Table 2).

Table 2.

Pathological, clinical responses and treatments

	Per-protocol population [n (%)]
Total pathological complete response	19 (63.3)
Pathological complete response in breast	20 (66.7)
Residual cancer burden score
RCB-0	18 (60.0)
RCB-1	4 (13.3)
RCB-2	4 (13.3)
RCB-3	4 (13.3)
Objective response rate
Complete response	4 (13.3)
Partial response	22 (73.3)
Stable disease	4 (13.3)
Initial dosing (400 mg)	13
Dose reductions	9 (69.2)
Delays	7 (53.8)
tPCR	9 (69.2)
Initial dosing (320 mg)	17
Dose reductions	3 (17.6)
Delays	9 (52.9)
tPCR	10 (58.8)

Figure 2.

Exploratory subgroup analyses of tpCR by baseline factors. Data are presented as tpCR rate (%) and 95% CI. The black squares indicate the tpCR rates following stratifications. TpCR, total pathological complete response; IHC, immunohistochemistry; FISH, fluorescence in situ hybridization; CI confidence interval.

The median follow-up period was 20 months (range from 11 to 30 months) for these 30 patients. Only one patient with stable disease after neoadjuvant therapy had metastatic disease in the brain with an EFS time of 14 months.

Safety

Thirty-four patients were included in the safety analysis. Adverse events are summarized in Table 3. All 34 patients experienced at least one AE of any grade. The most common AEs of any grade were diarrhea (100%), leukopenia [30 (88.2%)], neutropenia [27 (79.4%)], anemia [22 (64.7%)], oral mucositis [20 (58.8%)], and vomiting [16 (47.1%)]. Grade 3 AEs included diarrhea [17 (50.0%)], neutropenia [7 (20.6%)], leukopenia [6 (17.7%)], decreased platelet count [1 (2.9%)], and decreased lymphocyte count [1 (2.9%)]. The median duration of Grade 3 AE of diarrhea was 2 days, which occurred in the first cycle of treatment. One patient discontinued dalpiciclib because of Grade 3 decreased platelet count in cycle three. All these AEs were manageable, and no Grade 4 events or treatment-related deaths occurred.

Table 3.

Treatment-emergent adverse events

Adverse events	No. (%)
	Any grade	Grade 3
Diarrhea	34 (100)	17 (50.0)
Leukopenia	30 (88.2)	6 (17.7)
Neutropenia	27 (79.4)	7 (20.6)
Anemia	22 (64.7)
Oral mucositis	20 (58.8)
Vomiting	16 (47.1)
Rash	10 (29.4)
Increased creatinine levels	8 (23.5)
Decreased platelet count	7 (20.6)	1 (2.9)
Nausea	6 (17.7)
Fatigue	6 (17.7)
Stomachache	4 (11.8)
Lymphocyte count decreased	4 (11.8)	1 (2.9)
Fever	3 (8.8)
Pharyngitis	3 (8.8)
Nasal mucosa ulceration	2 (5.9)
Hematochezia	2 (5.9)
Hyperuricemia	2 (5.9)
Hypertriglyceride disease	1 (2.9)
Hand-foot syndrome	1 (2.9)
Salivation	1 (2.9)
Giddy	1 (2.9)

Discussion

The XYBC-01 trial evaluated the efficacy and safety of neoadjuvant therapy with trastuzumab and pyrotinib plus dalpiciclib in patients with HR-HER2+ breast cancer. The therapeutic regimen exhibited an exciting anti-tumor activity with a tpCR rate of 63.3% and some acceptable adverse events.

The chemotherapy-free regimens for HER2+ breast cancer have achieved an exciting success; however, there are a few questions that deserve our consideration. First, some clinical trials used only one anti-HER2 drug, rather than dual anti-HER2 drugs, for patients with HER2+ breast cancer in the neoadjuvant setting. However, it is well known that dual anti-HER2 drugs have superior efficacy compared to single drug treatment in HER2+ disease^[18,19]. The DAP-HER-01 trial, which administered dalpiciclib and pyrotinib for patients with metastatic HER2+ disease, showed an ORR of 70% and a median PFS of 11 months[15]. The MUKDEN-01 trial tested the value of pyrotinib and letrozole plus dalpiciclib for patients with early HR+HER2+ breast cancer and obtained a pCR rate of 30.4%[19]. Nevertheless, the authors from DAP-HER-01 and MUKDEN-01 trials had admitted that it would be more rational to add trastuzumab to the regimen for HER2+ disease. So, the dual anti-HER2 therapy should be considered the standard treatment for HER2+ disease with heavy tumor burden during the neoadjuvant, adjuvant, and metastatic settings. Therefore, we applied a dual anti-HER2 regimen of trastuzumab and pyrotinib for HER2+ disease in our trial.

The second question is which combination of dual anti-HER2 is better, trastuzumab plus pertuzumab or trastuzumab plus tyrosine kinase inhibitor? The NeoSphere trial with the treatment of trastuzumab and pertuzumab for early HER2+ disease obtained a pCR rate of 16.8%, and the PHERGain trial with trastuzumab and pertuzumab, without or with endocrine therapy, showed a pCR rate of 37.9% for patients with early HER2+ disease responding to the first two cycles of treatment^[4,20]. In the TBCRC 006 and TBCRC 023 trials, patients receiving trastuzumab and lapatinib, without or with letrozole, obtained the pCR rates of 27.0% and 12.0%, respectively^[6,7]. The pCR rate seems to be improved if the duration of treatment is extended, as shown in the PAMELA and TBCRC 023 trials^[7,21]. However, we have no direct evidence to prove which is the best partner for trastuzumab, pertuzumab, or a tyrosine kinase inhibitor. Nevertheless, we know that pyrotinib, an irreversible pan-ErbB receptor tyrosine kinase inhibitor, has been shown to be more effective than lapatinib for HER2+ metastatic disease in the PHOEBE trial, and is approved for the treatment of HER2+ breast cancer in the metastatic and neoadjuvant setting in China^[2,22,23]. We presume that the combination of trastuzumab and pyrotinib in our trial might lead to a higher pCR rate for patients with HR-HER2+ breast cancer in the neoadjuvant setting compared with 36.0% and 18.0% from TBCRC 006 and TBCRC 023, respectively^[6,7]. In fact, we have obtained the tpCR rate of 63.3% in our trial, and reached the primary endpoint.

The third question is that some aforementioned trials were mainly focused on the subgroup of HR+HER2+ breast cancer, and tended to strengthen the endocrine therapy with CDK4/6 inhibitor to achieve a better therapeutic effect^[14,24]. However, preclinical studies showed that the cyclin D/CDK 4/6 compounds are directly downstream of the HER2 pathway, and inhibition of CDK 4/6 would synergize with anti-HER2 agents to suppress the proliferation and invasion of HER2+ breast cancer cells, not just in HR+HER2+ breast cancer cells^[10,25–27]. So, it is reasonable to use a CDK4/6 inhibitor in HER2+ breast cancer, regardless of HR status. But the use of CDK4/6 inhibitors in HR-HER2+ advanced breast cancer has obtained inconsistent results. Goel et al used the combination of a low dose of CDK4/6 inhibitor ribociclib (400 mg) and trastuzumab in patients whose median number of prior lines of systemic therapy for metastatic HER2+ disease was five. There were 12 patients in this trial, and 4 of them had HR-HER2+ disease. None of the four patients reached the primary endpoint of stable disease >24 weeks. The poor efficacy of this combination might be due to the heavily pretreated population and the reuse of trastuzumab[11]. Ciruelos et al used another CDK4/6 inhibitor palbociclib 200 mg daily for 2 weeks and 1 week off plus trastuzumab for 15 patients with HR-HER2+ disease in the SOLTI1303-PATRICIA study. The primary endpoint of PFS rate at 6 months was 33.3%[12]. The efficacy from Ciruelos et al was much better than that from Goel et al (33.3% versus 0%). This might be attributed to the different prior lines of systemic anti-HER2 therapy for metastatic disease. In the SOLTI1303-PATRICIA trial, the median number of prior lines of treatment was three, which was fewer than that from Goel et al trial. The DAP-HER-01 trial enrolled HER2+ patients with no more than one line of prior systemic treatment for advanced disease, and used dalpiciclib and pyrotinib as the therapeutic regimen. Of note, an ORR of 81.8% and a median PFS of 19.3 months were obtained for patients with HR-HER2+ disease[15]. The reasons for the high ORR and long PFS might be the administration of pyrotinib for tyrosine kinase inhibitor-naïve patients regardless of trastuzumab-sensitive or -resistant and the cohort of untreated HER2+ patients in the context of metastatic disease. In our trial, we administered the combined therapeutic regimen with trastuzumab and pyrotinib and dalpiciclib for patients with HR-HER2+ disease in the neoadjuvant setting and obtained encouraging results of tpCR of 63.3% and bpCR of 67.7%.

The survival follow-up is not yet mature. We had one patient with metastatic disease in the brain during the follow-up period who had stable disease after the triplet-regimen neoadjuvant therapy. This patient had received anthracycline and paclitaxel-based chemotherapy after surgery and trastuzumab plus pertuzumab as the targeted therapy. However, this patient developed metastatic disease after 16 cycles of targeted therapy. Although the blood–brain barrier penetration of pyrotinib and other TKIs was well known, given that the primary tumor was not sensitive to the triplet therapy, it is not surprising that the HER2-positive disease relapsed in the brain.

Ki-67 is a common clinical measure of tumor cell proliferation and a prognostic biomarker in invasive breast cancer[28]. In our trial, there were 20 patients with no residual disease in the breast. The analysis of Ki-67 change was not appropriate due to the unavailability of specimens from surgery. So, we did not analyze the changes in Ki-67 in this study.

The regimen tested in the XYBC-01 trial was tolerable, with some known profile of AEs, and no Grade 4 AEs or treatment-related deaths in this population. Diarrhea, which is easily manageable, emerged as the most frequent side effect. Grade 3 diarrhea only lasted for 2 days in most cases, and most of them turned to mild events when a suitable intervention was applied. The preventive use of SMECTA or loperamide was permitted, but patients in this study did not take the suggestion of preventive use before the diarrhea occurred. The high frequency of Grade 3 diarrhea (50%) in this study was similar to the reports from the PANPHILA and PHEDRA trials, which applied the regimen of pyrotinib plus trastuzumab-based chemotherapy in the neoadjuvant setting with frequencies of 43.2% or 44.4% of Grade 3 diarrhea, respectively^[22,29]. In the PANDORA trial, pyrotinib plus docetaxel was used as first-line treatment for HER2+ metastatic breast cancer; 8.9% of patients who had received loperamide prophylaxis suffered Grade 3 diarrhea compared with 38.2% of patients who did not[30]. Although we have reduced the initial dose of pyrotinib from 400 to 320 mg, the occurrence of Grade 3 diarrhea was not decreased substantially. So, loperamide prophylaxis and dose escalation of pyrotinib might be the ways to prevent the occurrence of serious diarrhea in the future. Leukopenia and neutropenia were also common; however, no intervention was needed for these non-perception events, and delay of dalpiciclib did not happen. We also noticed the Grade 1–2 oral mucositis which might influence the appetite of patients; nevertheless, it was less severe than chemotherapy-related AEs, such as alopecia, vomiting, and fatigue. In brief, the chemotherapy-free regimen with trastuzumab, pyrotinib, and dalpiciclib provides an alternative option for patients with HR-HER2+ breast cancer.

There are some limitations in our study. First, the small sample size and lack of a control group restrict the interpretability of the promising pCR rate in our study, which is higher than that from the TBCRC 006 and TBCRC 023 trials. We have already planned a non-inferiority trial to test the therapeutic efficacy of the combination of the triplet drugs in patients with HR-HER2+ breast cancer compared with the regimen of chemotherapy plus trastuzumab and pertuzumab (ChiCTR2500097681). Second, our study was a single-arm, investigator-initiated trial, and our original plan was to enroll HER2+ patients; however, in the end we only included HR-HER2+ individuals because of difficulty in enrollment. That means our results can only apply to this cohort of patients with HR-HER2+ disease. Third, patients in our study who achieved a complete response to the triplet-regimen therapy would be allowed to omit chemotherapy if they agreed, and continue with the triplet-regimen therapy for another 7 months. Patients with residual disease received four to eight cycles of chemotherapy plus trastuzumab and pertuzumab for another 1 year. Although there is no standard adjuvant therapy for patients with no residual disease after surgery in our study, no recurrent event has been identified in these patients until now. Fourth, the potential mechanisms by which CDK4/6 inhibitors could strengthen the therapeutic efficacy of trastuzumab and pyrotinib in patients with HR-HER2+ disease and why some patients were resistant to the triplet-regimen therapy remain unclear. More basic biomolecular research studies are needed to answer these questions.

In conclusion, the neoadjuvant therapy with trastuzumab, pyrotinib, and dalpiciclib was tolerated and achieved promising therapeutic efficacy in patients with HR-HER2+ breast cancer. This chemotherapy-free therapy with high pathological response has the potential to be an alternative treatment for patients with HR-HER2+ breast cancer. Further validation of these findings in a large cohort randomized controlled trial is warranted.

Ethical approval

This study was approved by the ethics committee of Xiangya Hospital of Central South University (reference number: 快202205250).

Consent

Written informed consent was obtained from each patient before enrollment.

Sources of funding

This study was funded by the Special Research Project for Clinical Research of Innovative Drugs after Market Launch (WKZX2024CX103103), the Science and Technology Innovation Plan Project in Hunan Province (2022SK2041), the Key Research and Development Program of Hunan Province (2025JK2123), and the Natural Science Foundation of Hunan Province (2024JJ9133).

Author contributions

Conception and design: Z.X. and S.W.; provision of study materials or patients: F.C., L.L., S.L., Xu.L., Xi.L., T.X., Y.H., N.L. and J.H.; collection and assembly of data: W.W., J.C., and Z.X.; data verification: K.W., H.Z., Z.X., and S.W.; statistical analysis: Z.X. and S.W.; data analysis and interpretation: all authors; preparation and critical revision of the paper: Z.X. and S.W.; study supervision: Z.X. and S.W.; and final approval of paper: all authors.

Conflicts of interest disclosure

The author declares no conflict of interest.

Research registration unique identifying number (UIN)

Our study has been registered on http://www.chictr.org.cn/index.aspx under the registration number Chi-CTR-2200060748. Hyperlink to our specific registration is Chinese Clinical Trial Registry - World Health Organization International Clinical Trials Registry Platform Level 1 Registration Institution.

Guarantor

Shouman Wang.

Provenance and peer review

Not commissioned, externally peer-reviewed.

Data availability statement

The raw clinical and imaging data are protected and not available due to patient privacy laws. The de-identified datasets supporting the findings of this study are available for academic purposes on request from the corresponding author, for 5 years, with the approval of the Institutional Ethical Committee.

Assistance with the study

None.

Presentation

None.