STAT3, a Poor Survival Predicator, Is Associated with Lymph Node Metastasis from Breast Cancer

Breast cancer, as an increasing incidence malignancy, is the most common lethal disease in females [1]. Most breast cancer patients have lymph node metastasis when they are initially diagnosed or operated on, which results in a poor prognosis [2]. Although there was no significant improvement on disease-free survival (DFS) and overall survival (OS), lymph node dissection was recently identified to reduce the local recurrence rate in breast cancer patients with node micrometastasis [3]. To date, sentinel lymph node biopsy (SLNB) has become the standard of care as a staging procedure for breast cancer patients with clinically node-negative disease, and regional nodal irradiation after a positive SLNB has been considered as a reasonable alternative to axillary lymph node dissection (ALND) [4]. ALND remains a standard method of treating regional disease not only in patients with clinically positive nodes but also in some SLNB positive patients [5], while the latest researches demonstrated that most SLNB positive patients would be candidates to avoid ALND if they underwent breast-conserving therapy (BCT) [6, 7]. Therefore, the accurate evaluation of lymph node metastasis is very important to the procedure of surgery, in addition to the predication the prognosis of breast cancer patients. Unfortunately, there is not an authoritative method for detection the nodal metastasis from breast cancer before surgery. On the other hand, we have to admit the fact that there is not a satisfactorily biomarker with the high specificity and sensitivity for screen the relapse of patients following the mastectomy. Lymphatic metastasis represents a series of sequential processes that include the dissemination and invasion of tumor cells from the primary tumor into the surrounding stromal tissue, penetration of the tumor cells across the lymphatic walls, implantation in the regional lymph nodes, and extravasation and proliferation in the parenchyma of target organs [7]. In general, vascular endothelial growth factor (VEGF)-C and -D have been defined as lymphangiogenic growth factors and play an important role in tumor lymphangiogenesis via activation of the VEGF receptor (VEGFR)-3, which is expressed in lymphatic endothelial cells [8, 9]. However, these two biomarkers can not provide the information of dissemination and invasion of tumor cells, penetration of the tumor cells, and so on. These aforementioned defects make VEGF-C and -D not to be widely applicable to diagnosis the lymph node metastasis or to screen the nodal relapse in clinic.

Signal transducer and activator of transcription 3 (STAT3), an important member of the STAT family, is a latent transcription factor that has been shown to act as an oncogene in several malignant diseases [10]. It is well known that STAT3 is activated (phosphorylated STAT3, pSTAT3) in response to the binding of a large number of cytokines, hormones and growth factors to their receptors. Actually, STAT3 has been demonstrated to up-regulate genes encoding apoptosis inhibitors (Bcl-xL, Mcl-1, and survivin), cell-cycle regulators (cyclin D1 and c-Myc) and angiogenesis inducers (e.g., VEGF), which are important molecular cub for tumor progression [11-13]. Recently, several investigators reported that STAT3 aberrant expression were significantly associated with the status of lymph node metastasis in various malignant disease [14-19]. Theoretically, STAT3 has the ability to promote the lymphatic metastasis from malignancy. The detailed correlation between lymph node metastasis and STAT3 expression is not elucidated.

In view of aforementioned causalities, we designed this study for exploration the implication of the STAT3 aberrant expression in breast cancer. They are as follows: 1) to elucidate the STAT3 aberrant expression for predication the OS of breast cancer patients after curative resection; and 2) to initially analyze the correlation between the STAT3 aberrant expression and lymph node metastasis from breast cancer.

Lymph node metastasis from breast cancer is a complex pathophysiological process of cancer progress, which is mainly associated with the biological habits of cancer cells. Usually, biological factors may directly affect the end-results of the malignant cells to selectively invade lymph nodes rather than visceral organs, just as certain tumor types metastasize to certain organs and not others [20]. Exact recognition of the lymph node metastatic status is considered as the important clue for contribution to not only choice the appropriate surgical procedure of lymph node dissection, but improvement the prognostic predication. To date, SLNB has become the standard of care as a staging procedure for breast cancer patients with clinically node-negative disease [5]. The current guidelines recommend completion ALND when lymph node involvement is identified by SLNB [4], although the need for completion ALND has been questioned [2]. Kim et al. [21] reported that approximately 50% of patients had additional nonsentinel axillary nodal metastases, which indicated that ALND might improve the prognosis of breast cancer patients. Furthermore, Park et al. [6] found that axillary recurrences were more frequent in a group of 287 patients who underwent SLNB alone compared with those who underwent completion ALND (2.0% vs. 0.4%, p=0.004). Therefore, we have to believe that the exact diagnosis of nodal metastasis from breast cancer is a crucial factor for application the correctly surgical procedure and decrease the recurrence rate.

However, there is not an optimal method for exact detection the lymph node metastatic status before surgery. The insidiously nodal metastasis and micrometastasis of lymph nodes are so difficult to be detected with the general examinations. Biomarkers are high hopes for accurate prediction the lymph node metastasis from primary tumor. In theory, cancer cell metastasis should be considered to involve the cell proliferation, antiapoptosis, invasion enhancement, and lymphangiogenesis. According to these biological characteristics, STAT3, a cub of molecular regulator in various malignancies, is competent to evaluate the lymph node metastasis, rather than other conventional lymphangiogenetic factors [10-13].

In many solid tumors, overexpression of human epidermal growth factor receptors (e.g., HER1/EGFR and HER2) correlates with poor prognosis. As a poor prognostic factor, EGFR overexpression is frequently shown in the breast cancer cells and tissues [22]. The key one of the down-stream molecules of EGFR which is identified to the oncogenesis in various organs is STAT3 [23]. Actually, STAT3 is constitutively activated by aberrant upstream tyrosine kinase activities in a broad spectrum of cancer cell lines and human tumors. STAT3 is an oncogenic protein that is constitutively activated in many human cancers, including 30% to 60% of primary breast cancers [22]. The biological significance of STAT3 activation in breast cancer is not fully understood. STAT3 activation may modulate tumor invasiveness of breast cancer by regulating TIMP1 expression. Pytowski et al. [24] generated an in vitro system in which active STAT3 levels can be tightly controlled in breast cancer cells by using MCF-7 cells transfected with tetracycline-off constitutively active STAT3. Using immunohistochemistry and 142 primary breast tumors, they also found a significant association between the expression of the phosphorylated/active form of STAT3 (pSTAT3) and that of tissue inhibitor of matrix metalloproteinases-1 (TIMP-1) [24]. At present study, we demonstrated there were significantly statistical differences in the positive expression incidences of STAT3, and pSTAT3 between breast cancer and adjacent non-tumor tissue specimens. In addition, we also found that both STAT3 expression and pSTAT3 expression were significantly associated with the OS of breast cancer patients after curative resection. Therefore, we did consider that STAT3 was a pivotal biomarker for predication the prognosis of breast cancer. As other investigators reported, STAT3 was significantly associated with the bad prognosis in various human malignancies [18, 25-27].

Lymph node metastasis was well known as the most important predicator of prognosis of breast cancer after surgery. Recently, several investigations demonstrated that STAT3 was involved in a series of molecular events of lymph node metastasis in different human cancers [11-15]. From the results of this study, we found that lymph node metastasis was the only independent predicator of the OS of breast cancer patients after surgery. Although we demonstrated that nine variables (including VEGF-C expression, VEGF-D expression, and Ki-67 expression) that had statistically significant associations with lymph node metastasis from breast cancer, the STAT3 expression was the most important predicator of lymph node metastasis from breast cancer by using the multinomial logistical regression model analysis rather than other variables.

Notwithstanding a small scale study was performed, we concluded that STAT3 might improve the cancer cell lymphatic metastasis, which induced the bad prognosis of breast cancer patients. The anti-STAT3 monoclonal antibody might change treatment status in the nodal metastasis from breast cancer, which is worthy of hoping for further improvement the prognosis of patients.