[Correlation of STAT6 and HER2-low expression with clinicopathological features and prognosis in triple negative breast cancer].

Objective: To investigate the expression of STAT6 and HER2 in triple negative breast cancer (TNBC) and their relationship with clinicopathological features and prognosis. Methods: A total of 189 TNBC samples, including 32 cases with tumor and surrounding normal tissues from Peking Union Medical College Hospital from 2000 to 2011 were collected and tissue microarrays were made. The expression of STAT6 in tumor cells and normal breast tissues was evaluated by immunohistochemistry, and the difference between them were analyzed. The expression of HER2 was classified into 0 and low expression. The relationship with clinicopathological parameters and the prognosis was analyzed. Results: The 57.1% (108/189) cases showed STAT6 high expression, 34.4% (65/189) showed HER2 low expression, and 27.0% (51/189) showed co-expression. The expression of STAT6 in normal breast tissue was lower than that in tumor (t=-5.549, P<0.01). Chi-square test showed that compared with STAT6 low patients, STAT6 high had higher HER2-low, and lower distant metastasis rate (17.3% vs. 47.2%, P<0.01; 22.3% vs. 39.2%, P=0.013); compared with HER2-0 patients, HER2-low had higher STAT6-high, and lower distant metastasis rate (46.0% vs. 78.5%, P<0.01; 16.1% vs. 36.7%, P=0.004). Follow-up was 70(54,95) months, 7 patients (7/189, 3.7%) were lost to follow-up, 68 patients (68/189, 36.0%) relapsed, and 36 patients passed away (36/189, 19.0%). Kaplan-Meier survival analysis showed that tumor size, American Joint Committee on Cancer (AJCC) stage, lymph node metastasis, distant metastasis, and STAT6-low/HER2-0 were negatively correlated with the disease-free survival (DFS) and the overall survival (OS, all P<0.05). STAT6-high, HER2-low expression and STAT6-high/HER2-low were positively correlated with DFS and OS (all P<0.05). Age was only positively associated with OS (P=0.030). COX regression analysis showed that TNBC patients with higher AJCC stage had significantly shorter DFS and OS (HR=8.415, 95%CI: 3.623-19.544, P<0.001; HR=15.377, 95%CI:3.508-67.395,P<0.001); TNBC patients with STAT6-high/HER2-low had significantly longer DFS and OS, which was an independent risk factor for prognosis (HR=0.362, 95%CI: 0.186-0.705, P=0.003; HR=0.168, 95%CI: 0.038-0.743, P=0.019). Conclusions: In triple-negative breast cancer, the expression of STAT6 is higher than that in normal breast tissue. High expression of STAT6 is significantly correlated with HER2-low expression. STAT6-high/HER2-low may predict a good prognosis.