INTRODUCTION

Breast cancer is the most common cancer seen in women. According to Globocan 2020, 23.9% of cancers seen in women in our country are breast cancer. Breast cancer is the second most common cause of cancer mortality in our country and in the USA^1,2. Neoadjuvant treatment of breast cancer refers to the systemic treatment of the tumor before surgery. In this way, by shrinking the tumor, breast-conserving surgery can be performed instead of mastectomy, and better cosmetic results can be obtained, and lymphedema that may develop after surgery can be prevented^3,4. Another important advantage of neoadjuvant therapy is that therapeutic efficacy can be directly observed⁵. It also provides the opportunity for personalized treatment strategies and drug development⁶. Human epidermal growth factor receptor 2 (HER2) is from the family of epidermal growth factor receptors that play a critical role in the activation of subcellular signal transduction pathways which control epithelial cell growth and differentiation^7,8. Amplification or overexpression of the HER2 oncogene is present in approximately 15% of invasive breast cancers⁹. Since the presence of HER2 expression is a predictive factor in breast cancer, HER2 expression status should be investigated at the time of diagnosis in breast cancer¹⁰. In this way, agents targeting HER2 receptors can be used in adjuvant or neoadjuvant therapy^11-13. To determine the response after neoadjuvant therapy, pathological evaluation of the primary tumor and axillary lymph node is performed, except for negative sentinel lymph node before treatment. The absence of breast and axillary tumors in surgical material indicates pathological complete response (pCR) and is associated with better survival^14,15. Even if HER2-targeting agents are not used in neoadjuvant therapy in HER2 positive breast cancers, they have better pathological response rates than HER2-negative patients^16,17. Obtaining pCR after the completion of neoadjuvant therapy and surgical resection is associated with improved disease-free survival. This correlation is dependent on the molecular subtype and is evident in patients with triple negative and HER2 positive breast cancer⁵.

In our study, we aimed to determine the factors affecting the pathological response after neoadjuvant chemotherapy in HER2 positive breast cancer.

MATERIALS AND METHODS

From a total of 114 stage II and stage III breast cancer women with axillary lymph node involvement, who received neoadjuvant chemotherapy, 54 patients with HER2 expression positive were included. CerbB2 status was determined by immunohistochemical method from the biopsy material of the patients before neoadjuvant chemotherapy. Patients with cerbB2 negative status and 1+ were considered HER2 negative. HER2 expression was evaluated by fluorescent in situ hybridization method (FISH) from the tissues of patients with cerbB2 status of 2++, and those who were positive were considered HER2 positive. Patients with cerbB2 status of 3+++ were considered HER2 positive. Neoadjuvant chemotherapy regimen containing trastuzumab was given to all patients who were considered HER2 positive. Those with estrogen or progesterone receptor levels of ≥1% were considered hormone receptor positive, and those with both <1% were considered hormone receptor negative. Stage, tumor size and lymph node evaluation (TN) according to the American Joint Committee on Cancer (AJCC) TNM Staging Classification for breast cancer 8^th edition staging system including age, gender, tumor size, lymph node positivity and metastasis status of the patients and estrogen progesterone receptor status, Ki-67 proliferation index, tumor grade, menopausal status and pCR status after neoadjuvant treatment, neoadjuvant treatment regimen that was given, and histological subtype of the tumor were evaluated (Table 1).

Statistical Analysis

After testing the conformity of the data to the normal distribution, those showing normal distribution of continuous variables were analyzed with the t-test, and those that did not show normal distribution were analyzed with the Mann-Whitney U test. The χ² test was used in the analysis of categorical variables. All numerical data were expressed as mean values or ratios. For data that did not show normal distribution, comparisons between pre-post measurements were made using the Wilcoxon test.

Cox regression analysis was used to analyze univariate and multivariate data. Receiver operating characteristic (ROC) curve analysis was used to determine the Ki-67 cut-off value. Results were expressed as mean±standard deviation, median (lower limit and upper limit), number and percentage, and the value of p<0.05 was considered statistically significant. Statistical analysis of the data was performed using Statistical Package for the Social Sciences 21.0 software.

This article was approved by Çukurova University Faculty of Medicine Non-Invasive Clinical Research Ethics Committee with the decision number of 54 dated 10.06.2016.

RESULTS

Patient Characteristics

All of the patients participating in the study were women. A total of 114 patients who received neoadjuvant chemotherapy were evaluated. Twenty-eight (24.6%) patients were cerbB2 negative, 4 (3.5%) patients were cerbB2 1+, 35 (30.7%) patients were cerbB2 2++ and 47 (41.2%) patients were cerbB2 3+++. HER2 expression was detected by FISH method in 7 (6%) of 35 patients with CerbB2 2++. A total of 54 (47.3%) HER2 positive patients were evaluated. The median age of the patients included in the study was 52 years (age range: 34-76 years). The median Ki-67 score was 54% (range 5-90%), 20 (37%) patients had a Ki-67 score >50%, and 16 (29.6%) patients were hormone receptor negative. Approximately half of the patients had grade III tumors (n=28, 51.9%) and 29 (53.7%) patients were in the postmenopausal period. While docetaxel, carboplatin, trastuzumab (TCH) chemotherapy protocol was applied to 25 (46.3%) patients, dose-intensive Doxorubicin and cyclophosphamide/paclitaxel+trastuzumab chemotherapy protocol was applied to 23 (42.6%) patients. Reimbursement for pertuzumab was not available in our country at the time when the patient data were collected. Patients were offered this treatment option, but no patient accepted. Fourty-seven (87%) of the patients had stage III disease and approximately half had T4 tumor (n=25, 46.3%) while two-thirds had N2 (n=34, 63%) disease. When the histological subtypes of the tumors were examined, invasive ductal carcinoma was found in 40 (74.1%) patients.

Relationship Between Pathological Response and Clinicopathological Data

pCR was obtained in 30 (55.6%) of 54 patients. Clinicopathological data of the patients are shown in Table 1.

When the relationship between pCR and clinicopathological data was examined, no correlation was found among patients’ age, menopausal status, estrogen or progesterone receptor positivity, cerbB2 positivity, neoadjuvant chemotherapy protocols, N status and disease stage according to the TNM staging system, and histological subtype of the tumor (p>0.05). Higher rate of pCR was detected in the presence of grade III tumor, hormone receptor negativity, high Ki-67 score, and T3 or T4 tumors (p=0.036, p=0.033, p=0.021 and p=0.048, respectively) (Table 2). In the multivariate analysis performed to determine whether the variables associated with pCR were an independent risk factor, the presence of high tumor grade, negative hormone receptor and high Ki-67 score were found to be independent risk factors determining pCR after neoadjuvant therapy in HER2 positive breast cancer patients (p=0.043, p=0.047, p=0.035, respectively) (Table 3).

The most sensitive and specific values for study variables were determined using ROC curve analysis: The cut-off value for Ki-67 was 27.5% (Figure 1).

DISCUSSION

In our study, we aimed to investigate the factors affecting pCR in patients with HER2-positive breast cancer, and we found that hormone receptor negative, high Ki-67 score and the presence of high-grade tumor were independent risk factors affecting pCR.

Cortazar et al.¹⁶ evaluated 12 international studies on neoadjuvant therapy. They found that HER2 positive patient group had higher pCR than those with hormone receptor negative. In the study of Untch et al.¹⁸, although a higher pCR was shown in hormone receptor negative patients, the hormone receptor status was not statistically significant other than survival. In our study, we found that the hormone receptor negative group had a higher rate of pCR, and we revealed that hormone receptor negativeness was an independent risk factor determining pCR alone in patients with HER2-positive breast cancer (HR: 1,758, 95% CI: 0.758-2,214).

In another study by Cortazar and Geyer¹⁹, it was stated that pCR was lower with neoadjuvant therapy in patients with low-grade tumors. However, it was emphasized in the study that this group was a hormone receptor positive group. In the study of Jarzab et al.²⁰, tumor grade, Ki-67 and estrogen, and progesterone receptor negativity were determined as pCR-related tumor parameters. The highest chance of pCR was observed in patients with high grade tumor and Ki-67 ≥20%. Tumor grade and estrogen receptor status were predictive for pCR independent of other analyzed parameters. In the study of Spring et al.²¹, it was reported that higher pCR rates were observed in patients with grade 3 tumors. In the study of Karatas et al.²² in our country, no significant relationship was found between pCR and T status, but a significant relationship was found with grade. In our study, we found that a higher rate of pCR was obtained with neoadjuvant therapy in high-grade breast cancer patients independent of hormone receptor status as in the hormone receptor negative group, and tumor grade was an independent risk factor, similar to hormone receptor negativity [hazard ratio (HR): 2,321, 95% confidence interval (CI): 1,325-2,712].

In the study of Silva et al.²³, it was shown that patients with high Ki-67 proliferation index had a better response to neoadjuvant chemotherapy and had a higher rate of clinical complete response. In this study, the cut-off value for Ki-67 was taken as 14% (p=0.005). In the study, different cut-off values in Ki-67 expression were also examined and it was found that with increasing cut-off value for the predictive test, its sensitivity decreased and its specificity increased. In our study, we showed that a Ki-67 proliferation index higher than 27.5% would provide a higher rate of pCR after neoadjuvant therapy, and we found it to be an independent risk factor.

In the study of Untch et al.²⁴, in which they evaluated pCR with neoadjuvant therapy in HER2 positive breast cancer patients, no difference was found between patients with tumors larger than 4 cm and those with tumors smaller than 4 cm. In our study, although there was a statistically significant difference in univariate analysis between patients with T1 or T2 (≤5 cm) tumors and patients with T3 or T4 (>5 cm) tumors for pCR, it was not found to be an independent risk factor in multivariate analysis.

Study Limitations

The limitations of our study are the lack of pertuzumab use and the small number of patients. Further studies with more patients treated with new targeted agents are needed.

CONCLUSION

Factors determining pCR after neoadjuvant therapy in HER2 positive breast cancer patients are Ki-67 proliferation index, tumor grade and hormone receptor negativity. Longer disease-free survival can be achieved by obtaining pCR with ideal neoadjuvant therapy in selected patient groups.

Ethics

Ethics Committee Approval: This article was approved by Çukurova University Faculty of Medicine Non-Invasive Clinical Research Ethics Committee with the decision number of 54 dated 10.06.2016.

Informed Consent: Retrospective study.

Peer-review: Externally peer-reviewed.

Authorship Contributions

Surgical and Medical Practices: A.E.Y., Concept: A.E.Y., S.P., Design: A.E.Y., S.P., Data Collection or Processing: A.E.Y., S.P., Analysis or Interpretation: A.E.Y., S.P., Literature Search: A.E.Y., S.P., Writing: A.E.Y., S.P.

Conflict of Interest: No conflict of interest was declared by the authors.

Financial Disclosure: The authors declared that this study received no financial support.