Serum HER2 levels predict treatment efficacy and prognosis in patients with HER2-positive breast cancer undergoing neoadjuvant treatment

Background: Controversy remains regarding the predictive and prognostic value of serum human epidermal growth factor receptor 2 (HER2) in breast cancer. The purpose of this retrospective study was to determine the clinical utility and efficacy of serum HER2 (sHER2) in predicting treatment response and prognosis in patients with HER2-positive breast cancer undergoing neoadjuvant chemotherapy and trastuzumab treatment. Methods: A total of 309 HER2-positive breast cancer patients diagnosed at Fudan University Shanghai Cancer Center from July 2015 to January 2019 were analyzed. Baseline sHER2 levels were obtained for all patients and sHER2 levels were collected after 2 cycles of treatment in 208 patients. A sHER2 level >= 15 ng/mL was regarded as "high expression" and sHER2 <15 ng/mL was regarded as "low expression". Outcome measures of treatment efficacy and prognosis were pathological complete response (pCR) and invasive disease-free survival (iDFS), respectively. Results: In patients with high baseline sHER2, more were ER-negative (P=0.029), had larger tumor size (P=0.006), more advanced clinical stage (P=0.002), higher Miller-Payne grade (P=0.024) and higher likelihood of iDFS events (P=0.015). Patients with high sHER2 levels after 2 cycles of treatment had lower pCR rates (P=0.038), higher Miller-Payne grade (P=0.013) and higher likelihood of iDFS events (P=0.003). Kaplan-Meier analysis showed significant differences in iDFS between patients with high and low sHER2 levels at baseline (P=0.019) and after 2 cycles of treatment (P=0.000). Further analyses according to cancer subtypes found baseline sHER2 to be significantly correlated with the iDFS of Luminal B patients (p=0.002), while sHER2 levels after 2 cycles of treatment was significantly correlated with the iDFS of HER2-enriched patients (P=0.000). Univariate analysis showed significant association between iDFS and tumor size (P=0.026), lymph node status (P=0.008), clinical stage (P=0.031), baseline sHER2 (P=0.024), overall tumor response (P=0.011), pCR (P=0.043) and Miller-Payne grade (P=0.001). Multivariate analysis found Miller-Payne grade (P=0.037) to be significantly associated with iDFS. Conclusions: Our results demonstrate the clinical value of sHER2 in a population of Chinese breast cancer patients, suggesting that sHER2 levels after 2 cycles of neoadjuvant therapy may be more predictive of treatment outcomes and that the prognostic value of sHER2 may be time point and subtype dependent.