Age-Related Incidence and Peak Occurrence of Contralateral Breast Cancer.

Importance: Young patients with breast cancer have higher risk for developing contralateral breast cancer (CBC) and have epidemiologic characteristics different from those of older patients. Objective: To examine the incidence and peak occurrence of CBC according to age at primary breast cancer (PBC) surgery. Design, Setting, and Participants: This cohort study included patients who were diagnosed with and underwent surgery for unilateral nonmetastatic breast cancer at Asan Medical Center, Korea, between January 1, 1999, and December 31, 2013, with follow-up through December 31, 2018. Data were analyzed from December 1, 2021, through April 30, 2023. Patients were divided into 2 groups according to their age at surgery for PBC: younger (≤35 years) vs older (>35 years). Main Outcomes and Measures: The main outcomes were cumulative incidence and hazard rate of CBC in the entire study population and in subgroups divided by cancer subtype, categorized according to hormone receptor (HR) and ERBB2 status. Results: A total of 16 251 female patients with stage 0 to III breast cancer were analyzed; all patients were Korean. The mean (SD) age was 48.61 (10.06) years; 1318 patients (8.11%) were in the younger group, and 14 933 (91.89%) were in the older group. Median follow-up was 107 months (IQR, 79-145 months). Compared with the older group, the younger group had significantly higher incidence of CBC (10-year cumulative incidence, 7.1% vs 2.9%; P < .001) and higher risk (hazard ratio, 2.10; 95% CI, 1.62-2.74) of developing CBC. The hazard rate, which indicates risk for developing CBC at a certain time frame, differed according to the subtype of primary cancer. In patients with the HR+/ERBB2- subtype, the risk increased continuously in both age groups. In patients with the triple negative subtype, the risk increased until approximately 10 years and then decreased in both age groups. Meanwhile, in the HR-/ERBB2+ subtype, risk peaked earlier, especially in the younger group (1.7 years since first surgery in the younger group and 4.8 years in the older group). Conclusions and Relevance: In this cohort study, patients aged 35 years or younger with breast cancer had a higher risk of developing CBC than older patients. Moreover, young patients with the HR-/ERBB2+ subtype tended to have a shorter interval for developing CBC. These findings might be useful in guiding treatment decisions, such as contralateral prophylactic mastectomy.

Survival Outcomes in Premenopausal Patients With Invasive Lobular Carcinoma.

Importance: The disparate prognostic implications between invasive ductal carcinoma (IDC) and invasive lobular carcinoma (ILC) have been demonstrated. However, information on premenopausal patients remains insufficient. Objective: To examine long-term survival outcomes of ILC and IDC in premenopausal patients using national databases. Design, Setting, and Participants: This cohort study used the Surveillance, Epidemiology, and End Results (SEER), Korean Breast Cancer Registry (KBCR), and Asan Medical Center Research (AMCR) databases to identify premenopausal patients with stage I to III ILC or IDC between January 1, 1990, and December 31, 2015. The median follow-up time was 90 (IQR, 40-151) months in the SEER database, 94 (IQR, 65-131) months in the KBCR database, and 120 (IQR, 86-164) months in the AMCR database. Data were analyzed from January 1 to May 31, 2023. Main Outcomes and Measures: The primary outcome was breast cancer-specific survival (BCSS), which was analyzed according to histological type, and the annual hazard rate was evaluated. Survival rates were analyzed using a log-rank test and a Cox proportional hazards regression model with time-varying coefficients. Multivariable analysis was performed by adjusting for tumor characteristics and treatment factors. Results: A total of 225 938 women diagnosed with IDC or ILC and younger than 50 years were identified. Mean (SD) age at diagnosis was 42.7 (5.3) years in the SEER database, 41.8 (5.5) years in the KBCR database, and 41.8 (5.5) years in the AMCR database. In terms of race (available for the SEER database only), 12.4% of patients were Black, 76.1% were White, 11.0% were of other race (including American Indian or Alaska Native, Asian, and Native Hawaiian or Other Pacific Islander), and 0.5% were of unknown race). Patients with ILC had better BCSS in the first 10 years after diagnosis than those with IDC (hazard ratios [HRs], 0.73 [95% CI, 0.68-0.78] in the SEER database, 1.20 [95% CI, 0.91-1.58] in the KBCR database, and 0.50 [95% CI, 0.29-0.86] in the AMCR database), although BCSS was worse after year 10 (HRs, 1.80 [95% CI, 1.59-2.02] in the SEER database, 2.79 [95% CI, 1.32-5.88] in the KBCR database, and 2.23 [95% CI, 1.04-4.79] in the AMCR database). Similar trends were observed for hormone receptor-positive tumors (HRs, 1.55 [95% CI, 1.37-1.75] in the SEER database, 2.27 [95% CI, 1.01-5.10] in the KBCR database, and 2.12 [95% CI, 0.98-4.60] in the AMCR database). Considering the annual hazard model of BCSS, IDC events tended to decline steadily after peaking 5 years before diagnosis. However, the annual peak event of BCSS was observed 5 years after diagnosis for ILC, which subsequently remained constant. Conclusions and Relevance: These findings suggest that premenopausal women with ILC have worse BCSS estimates than those with IDC, which can be attributed to a higher late recurrence rate of ILC than that of IDC. Histological subtypes should be considered when determining the type and duration of endocrine therapy in premenopausal women.

Survival After Development of Contralateral Breast Cancer in Korean Patients With Breast Cancer.

Importance: Contralateral breast cancer (CBC) is the most frequently diagnosed primary cancer in patients with breast cancer. Although many studies have reported survival after the development of CBC, results have been inconsistent. Objective: To investigate whether the development of CBC is associated with survival among patients with breast cancer. Design, Setting, and Participants: This cohort study was conducted at the Asan Medical Center, Korea, among patients who were diagnosed with primary unilateral, nonmetastatic, stage 0 to III breast cancer between 1999 and 2013 and followed up through 2018. The median (IQR) follow-up was 107 (75-143) months. Patients were categorized into CBC and no-CBC groups by whether they developed CBC during the follow-up period. Data were analyzed from November 2021 to March 2023. Exposure: Development of CBC. Main outcomes and measures: Survival rates of CBC and no-CBC groups were compared using a time-dependent Cox proportional hazard model in the entire study population and in subgroup analyses by interval of CBC development and subtype of the primary breast cancer. Results: Among 16 251 patients with breast cancer (all Asian, specifically Korean; mean [SD] age, 48.61 [10.06] years), 418 patients developed CBC. There was no significant difference in overall survival between CBC and no-CBC groups (hazard ratio, 1.166; 95% CI, 0.820-1.657). Patients who developed CBC within 1.5 years after the surgery of the primary breast cancer had a higher risk for overall death during the study period (hazard ratio, 2.014; 95% CI, 1.044-3.886), and those who developed CBC after 1.5 years showed no significant difference in survival compared with the no-CBC group. Patients with hormone receptor (HR)-positive and human epidermal growth factor receptor 2 (ERBB2, formerly HER2)-negative breast cancer had a higher risk for overall death in the CBC group (hazard ratio, 1.882; 95% CI, 1.143-3.098) compared with the no-CBC group. Conclusions and Relevance: This study found that development of CBC in patients with breast cancer was not associated with survival but that early development of CBC after diagnosis of the primary breast cancer or development of CBC in patients with HR-positive/ERBB2-negative breast cancer was associated with survival. These results may provide valuable information for patients seeking advice on opting for contralateral prophylactic mastectomy.

Artificial intelligence for predicting five-year survival in stage IV metastatic breast cancer patients: A focus on sarcopenia and other host factors.

We developed an artificial intelligence (AI) model that can predict five-year survival in patients with stage IV metastatic breast cancer, mainly based on host factors and sarcopenia. From a prospectively built breast cancer registry, a total of 210 metastatic breast cancer patients were selected in a consecutive manner using inclusion/exclusion criteria. The patients' data were divided into two categories: a group that survived for more than 5 years and a group that did not survive for 5 years. For the AI model input, 11 features were considered, including age, body mass index, skeletal muscle area (SMA), height-relative SMA (H-SMI), height square-relative SMA (H2-SMA), weight-relative SMA (W-SMA), muscle mass, anticancer chemotherapy, radiation therapy, and comorbid diseases such as hypertension and mellitus. For the feature importance analysis, we compared classifiers using six different machine learning algorithms and found that extreme gradient boosting (XGBoost) provided the best accuracy. Subsequently, we performed the feature importance analysis based on XGBoost and proposed a 4-layer deep neural network, which considered the top 10 ranked features. Our proposed 4-layer deep neural network provided high sensitivity (75.00%), specificity (78.94%), accuracy (78.57%), balanced accuracy (76.97%), and an area under receiver operating characteristics of 0.90. We generated a web application for anyone to easily access and use this AI model to predict five-year survival. We expect this web application to be helpful for patients to understand the importance of host factors and sarcopenia and achieve survival gain.

Psychiatric comorbidities and quality of life in breast cancer patients undergoing radiation treatment: Risk and protective factors.

OBJECTIVE: The primary goal was to evaluate the prevalence of psychiatric comorbidities and changes in psychological distress levels among breast cancer patients receiving radiotherapy (RT). The secondary goal was to determine risk and protective factors for psychiatric comorbidities of these patients. METHODS: From June 2018 to November 2019, patients were recruited from the hospital, Department of Psychiatry. Patients completed baseline surveys after seeing their radiation oncologist and prior to the first treatment, which was scheduled to take place within 7 days (visit 1, baseline); visit 2 occurred within 7 days after RT completion, and visit 3 occurred at 6 weeks after RT completion. A total of 99 patients participated in the study at visit 1; 56 patients completed the study through visit 3. RESULTS: Although changes in psychiatric comorbidities and overall quality of life were observed in patients with breast cancer prior to, during, and after RT, the differences were not significant among visits. Patients diagnosed with psychiatric comorbidities after RT had exhibited risk factors at previous visits, including preexisting psychiatric comorbidities, functional deterioration, and more severe symptoms related to breast cancer. Based on the results, the psychological characteristics of optimism and resilience can be considered as protective factors for psychiatric comorbidities. CONCLUSIONS: The results suggest that early detection and follow-up of psychological distress and poor quality of life at the onset of RT are of paramount importance, and that psychosocial interventions to enhance protective factors (optimism and resilience) may be helpful.

The effects of poloxamer and sodium alginate mixture (Guardix-SG®) on range of motion after axillary lymph node dissection: A single-center, prospective, randomized, double-blind pilot study.

PURPOSE: Restricted shoulder mobility is a major upper extremity dysfunction associated with lower quality of life and disability after breast cancer surgery. We hypothesized that a poloxamer and sodium alginate mixture (Guardix-SG®) applied after axillary lymph node dissection (ALND) would significantly improve shoulder range of motion (ROM) in patients with breast cancer. METHODS: We conducted a double-blind, randomized, prospective study to evaluate the clinical efficacy and safety of Guardix-SG® for the prevention of upper extremity dysfunction after ALND. The primary outcome measure was shoulder ROM at baseline (T0) and 3 (T1), 6 (T2), and 12 months (T3) after surgery. Secondary outcome measures were the Disabilities of the Arm, Shoulder, and Hand score(DASH), pain associated with movement, which was assessed using a numeric rating scale, and lymphedema assessed using body composition analyzer. RESULTS: A total of 83 women with breast cancer were randomly assigned to either the Guardix-SG® group or the control group. In the Guardix-SG® group (n = 37), Guardix-SG® was applied to the axillary region after ALND. In the control group (n = 46), ALND was performed without using Guardix-SG®. Comparing ROM for shoulder flexion before surgery (178.2°) and 12 months after surgery (172.3°), that was restored 12 months after surgery in the Guardix-SG® group, and there was no statistically significant difference between that at before surgery and 12 months after surgery (p = 0.182). No adverse effect was observed in either group. CONCLUSIONS: The results of this study have shown that Guardix-SG® help improve shoulder ROM without causing adverse effects in patients who underwent breast cancer surgery. However, there was no statistically significant difference from the control group. A further large-scale study is needed to obtain a more conclusive conclusion. TRIAL REGISTRATION: CRISKCT0003386; https://cris.nih.go.kr (20181207).

Age-related risk factors associated with primary contralateral breast cancer among younger women versus older women.

PURPOSE: Contralateral prophylactic mastectomy is increasing, despite unclear evidence of improving survival. To investigate the age-related risk factors for contralateral breast cancer (CBC). METHODS: This study included 8716 patients diagnosed with non-metastatic unilateral invasive breast cancer between 1989 and 2008. Data on primary tumor size, node metastasis, grade and subtype using individual matching were used to adjust for differences in the primary tumor and treatment between younger and older age groups. CBC risk factors, CBC-free survival, and annual CBC risk were analyzed by age. RESULTS: The younger group included 652 patients aged under 35 years, and the older group included 2608 women aged 35 years or older. The median time to CBC development was 6.1 years. CBC was detected in 6.6% of the women in the younger group and 2.5% of those in the older group. Multivariable analysis revealed a relative CBC risk of 2.48 in younger women compared to older women. The risk was significantly higher among women with human epidermal growth factor receptor 2 (HER2)-overexpressing tumors (hazard ratio [HR] 4.98), a family history of breast cancer (HR 7.79), and anti-hormone therapy (HR 3.46). In younger women with HER2-positive cancer, CBC occurrence peaked at 4.6 years after surgery, in those with hormone receptor-positive cancer, it peaked at 7.1 years after surgery, and in triple-negative disease cases, and it increased steadily over time. CONCLUSIONS: After adjusting for primary breast tumor characteristics, patients < 35 years old had 2.5 times the risk of CBC development compared to the older women. CBC occurrence peaked within 5 years after primary breast cancer in younger women with the HER2-positive subtype and after 5 years in cases with the hormone receptor-positive subtype.

Comparing Accuracy of Mammography and Magnetic Resonance Imaging for Residual Calcified Lesions in Breast Cancer Patients Undergoing Neoadjuvant Systemic Therapy.

BACKGROUND: Neoadjuvant systemic therapy (NST) is performed to increase the rate of breast-conserving surgery in advanced breast cancer patients. Although magnetic resonance imaging (MRI) is accurate in predicting residual cancer, if calcification remains, the issue of whether to perform the surgery on the basis of the residual tumor prediction range in mammography (MMG) or MRI has not yet been elucidated. This study aimed to estimate the accuracy of predicting residual tumor after NST for residual microcalcification on mammographic and enhancing lesion on MRI. PATIENTS AND METHODS: This was a single-center, retrospective study. We included breast cancer patients who underwent NST, had microcalcifications in the post-NST MMG, and underwent surgery from January 2, 2013 to December 30, 2014 at Asan Medical Center. Patients with post-NST MMG as well as MRI were included. Final pathologic tumor size with histopathology and biomarker status were obtained postoperatively. RESULTS: In total, 151 patients were included in this study. Overall, MRI correlated better than MMG in predicting the tumor size (intraclass correlation coefficient [ICC], 0.769 vs. 0.651). For hormone receptor (HR)-positive (HR+)/HER2- subtype, MMG had higher correlation than MRI (ICC = 0.747 vs. 0.575). In HR- subtype, MRI had a strong correlation with pathology (HR-/HER2+ or triple negative (TN), ICC = 0.939 vs. 0.750), whereas MMG tended to overestimate the tumor size (HR-/HER2+ or TN, ICC = 0.543 vs. 0.479). CONCLUSION: Post-NST residual microcalcifications on MMG have a lower correlation with residual tumor size than MRI. Other than HR+/HER2- subtype, the extent of calcifications on preoperative evaluation might not be accurate in evaluating the residual extent of the tumor after NST.

No Association of Positive Superficial and/or Deep Margins with Local Recurrence in Invasive Breast Cancer Treated with Breast-Conserving Surgery.

PURPOSE: We evaluated the effect of positive superficial and/or deep margin status on local recurrence (LR) in invasive breast cancer treated with breast-conserving surgery (BCS) followed by radiotherapy. MATERIALS AND METHODS: In total, 3,403 stage 1 and 2 invasive breast cancer patients treated with BCS followed by radiotherapy from January 2000 to December 2008 were included in this study. These patients were divided into three groups according to margin status: clear resection margin status for all sections (group 1, n=3,195); positive margin status in superficial and/or deep sections (group 2, n=121); and positive peripheral parenchymal margin regardless of superficial and/or deep margin involvement (group 3, n=87). The LR-free survival between these three groups was compared and the prognostic role of margin status was analyzed. RESULTS: Across all groups, age, tumor size, nodal status, and human epidermal growth factor receptor 2 status did not significantly differ. High grade, positive extensive intraductal component, hormone receptor positivity, hormone therapy received, and chemotherapy not received were more prevalent in groups 2 and 3 than in group 1. Five-year LR rates in groups 1, 2, and 3 were 1.9%, 1.7%, and 7.7%, respectively. Multivariate analysis revealed that group 3 was a significant predictor for LR (hazard ratio [HR], 4.78; p < 0.001), but that positive superficial and/or deep margin was not (HR, 0.66; p=0.57). CONCLUSION: Superficial and/or deep margin involvement following BCS is not an important predictor for LR.

Identifying long-term survivors among metastatic breast cancer patients undergoing primary tumor surgery.

PURPOSE: The prognostic role of primary tumor surgery in women with metastatic breast cancer at diagnosis is contentious. A subset of patients who will benefit from aggressive local treatment is needed to be identified. Using a nationwide database, we developed and validated a predictive model to identify long-term survivors among patients who had undergone primary tumor surgery. METHODS: A total of 150,043 patients were enrolled in the Korean Breast Cancer Registry between January 1990 and December 2014. Of these, 2332 (1.6%) presented with distant metastasis at diagnosis. Using Cox proportional hazards regression, we developed and validated a model that predicts survival in patients who undergo primary tumor surgery, based on the clinicopathological features of the primary tumor. RESULTS: A total of 2232 metastatic breast cancer patients were reviewed. Of these, 1541 (69.0%) patients had undergone primary tumor surgery. The 3-year survival rate was 62.6% in this subgroup. Among these patients, advanced T-stage, high-grade tumor, lymphovascular invasion, negative estrogen receptor status, high Ki-67 expression, and abnormal CA 15-3 and alkaline phosphatase levels were associated with poor survival. A prediction model was developed based on these factors, which successfully identified patients with remarkable survival (score 0-3, 3-year survival rate 87.3%). The clinical significance of the model was also validated with an independent dataset. CONCLUSIONS: We have developed a predictive model to identify long-term survivors among women who undergo primary tumor surgery. This model will provide guidance to patients and physicians when considering surgery as a treatment modality for metastatic breast cancer.

Survival improvement in hormone-responsive young breast cancer patients with endocrine therapy.

PURPOSE: We investigated the oncologic outcomes by intrinsic subtype and age in young breast cancer patients and whether survival differences were related to treatment changes over time. METHODS: A retrospective analysis was performed on 9633 invasive breast cancer patients treated at Asan Medical Center from January 1989 to December 2008. We also enrolled a matched cohort adjusting for tumor size, lymph node metastasis, subtypes, and tumor grade. Patients aged <35 years were included in the younger group (n = 602) and those aged ≥35 years were included in the older group (n = 3009). RESULTS: The younger patients showed a significantly higher T stage, a more frequent axillary node presentation, higher histologic grade, and higher incidence of triple-negative subtype tumors than older patients and also received more chemotherapy and were less likely to undergo hormone therapy. The younger patients with hormone receptor (HR)-positive tumors showed significantly poorer disease-free survival (DFS), loco-regional recurrence-free survival, distant metastasis-free survival, and breast cancer-specific survival outcomes than older patients. Younger patients with HR-positive and human epidermal growth factor receptor 2 (HER2)-negative tumor subtypes had a significantly improved DFS over time (p = 0.032). Within the HR-positive/Her2-negative subtype, more women received gonadotropin-releasing hormone agonist and tamoxifen treatment from 2003 to 2008 compared with 1989 to 2002 (p = 0.001 and p = 0.075, respectively). CONCLUSIONS: HR-positive young breast cancer patients have a poorer survival compared with older patients, even with more frequent chemotherapy, but more recent use of tamoxifen and ovarian suppression might improve this outcome in these patients.

Interaction between body mass index and hormone-receptor status as a prognostic factor in lymph-node-positive breast cancer.

The aim of this study was to determine the relationship between the body mass index (BMI) at a breast cancer diagnosis and various factors including the hormone-receptor, menopause, and lymph-node status, and identify if there is a specific patient subgroup for which the BMI has an effect on the breast cancer prognosis. We retrospectively analyzed the data of 8,742 patients with non-metastatic invasive breast cancer from the research database of Asan Medical Center. The overall survival (OS) and breast-cancer-specific survival (BCSS) outcomes were compared among BMI groups using the Kaplan-Meier method and Cox proportional-hazards regression models with an interaction term. There was a significant interaction between BMI and hormone-receptor status for the OS (P = 0.029), and BCSS (P = 0.013) in lymph-node-positive breast cancers. Obesity in hormone-receptor-positive breast cancer showed a poorer OS (adjusted hazard ratio [HR] = 1.51, 95% confidence interval [CI] = 0.92 to 2.48) and significantly poorer BCSS (HR = 1.80, 95% CI = 1.08 to 2.99). In contrast, a high BMI in hormone-receptor-negative breast cancer revealed a better OS (HR = 0.44, 95% CI = 0.16 to 1.19) and BCSS (HR = 0.53, 95% CI = 0.19 to 1.44). Being underweight (BMI < 18.50 kg/m2) with hormone-receptor-negative breast cancer was associated with a significantly worse OS (HR = 1.98, 95% CI = 1.00-3.95) and BCSS (HR = 2.24, 95% CI = 1.12-4.47). There was no significant interaction found between the BMI and hormone-receptor status in the lymph-node-negative setting, and BMI did not interact with the menopause status in any subgroup. In conclusion, BMI interacts with the hormone-receptor status in a lymph-node-positive setting, thereby playing a role in the prognosis of breast cancer.

Breast cancer-specific mortality in small-sized tumor with node-positive breast cancer: a nation-wide study in Korean breast cancer society.

Tumor size and number of lymph node (LN) metastases are well known as the most important prognostic factors of breast cancer. We hypothesized that very small breast cancers with LN metastasis represent a progressive biologic behavior and evaluated tumor size stratified by LN metastasis. Data between 1990 and 2010 were obtained retrospectively from the Korean Breast Cancer Society Registry with inclusion criteria of female, non-metastatic, unilateral, and T1/2 breast cancer. We collected the following variables: age at surgery, tumor size, number of LN metastases, nuclear grade (NG), lymphovascular invasion (LVI), estrogen receptor status, progesterone receptor status, and epidermal growth factor receptor-2 status. Patient characteristics were compared by means of independent t-tests for continuous variables and the Chi-square or Fisher's exact test for categorical variables. Kaplan-Meier curves, with corresponding results of log-rank tests, were constructed for breast cancer-specific survival (BCSS). Five- and eight-year breast cancer-specific mortality (BCSM) was obtained in groups of 300 patients, followed by smoothing according to the confidence interval using the lowess method. We identified 39,826 breast cancer patients who met the inclusion criteria. Among them, 1433 (3.6 %) patients died due to breast cancer. The median follow-up duration was 63.4 (3-255) months. In the multivariate analysis, age at surgery, NG, LVI, subtype, and tumor size-nodal interactions were independently associated with BCSM. The N1 group had lower BCSS for T1a than T1b. The N2+ group also had lower BCSS for T1b than T1c or T2. In the N1 group of tumors smaller than 10 mm, 5- and 8-year BCSM decreased with larger tumor size. Patients with very small tumors with LN metastasis have decreased BCSM according to increase tumor size. Small tumors with LN metastasis could have aggressive biological behavior.

Concurrent Gonadotropin-Releasing Hormone Agonist Administration with Chemotherapy Improves Neoadjuvant Chemotherapy Responses in Young Premenopausal Breast Cancer Patients.

PURPOSE: This study aimed to determine the oncologic efficacy of gonadotropin-releasing hormone (GnRH) agonist treatment concurrent with chemotherapy in a neoadjuvant setting. METHODS: A retrospective analysis was performed on 332 cases of invasive breast cancer in patients who were <40 years old at diagnosis and received GnRH agonists concurrent with neoadjuvant chemotherapy (GnRH agonist group) or neoadjuvant chemotherapy alone (neochemotherapy-alone group) from December 2010 to September 2014. Pathologic complete response rates (pCR) and Ki-67 changes were evaluated between the two groups. RESULTS: Median age was 32±3.9 and 36±3.0 years in the GnRH agonist group and neochemotherapy-alone group, respectively (p<0.001). After adjustment for tumor size, grade, lymph node metastasis, hormone receptor (HR) status, and chemotherapy regimen, the GnRH agonist group exhibited a higher pCR rate with an odds ratio (OR) of 2.98 (95% confidence interval [CI], 1.37-6.34) and a greater decrease in Ki-67 expression after treatment (p=0.05) than the neochemotherapy-alone group. For HR-negative tumors, the GnRH agonist group showed a higher pCR rate (multivariate OR, 3.50; 95% CI, 1.37-8.95) and a greater decrease in Ki-67 expression (p=0.047). For HR-positive breast cancer, the pCR rate, change in Ki-67 index, and clinical response were higher, and preoperative endocrine prognostic index scores were lower, in the GnRH agonist group, but these did not reach statistical significance. CONCLUSION: Concurrent administration of GnRH agonists during neoadjuvant chemotherapy improved pCR rates and suppressed Ki-67 expression, especially in HR-negative tumors.