Abstract P4-02-04: The significance of serum HER2 levels at diagnosis on outcome of breast cancer patients by molecular subtype

Background/purpose: Increased serum HER2 levels have been shown to correlate with higher tumor burden and poorer clinical outcomes in metastatic breast cancer, but there is little data regarding the significance of serum HER2 levels at diagnosis in the operable breast cancer. We evaluated the association between baseline serum HER2 levels and clinicopathologic parameters, and the correlation of baseline serum HER2 levels with clinical outcome by molecular subtype in operable breast cancer patients. Methods: We included patients with stage I-III breast cancer diagnosed at our center between October 2004 and December 2011. Baseline serum HER2 levels were measured by chemiluminescence immunoassay at diagnosis. Patients were categorized into 4 molecular subtype groups by their hormone receptor (HR) status and HER2 status: HR+/HER2-, HR+/HER2+, HR-/HER2+ and HR-/HER2-. HR and HER2 status were determined by immuhohistochemistry (IHC) in all tumors, and fluorescence in situ hybridization (FISH) assay was performed whenever the HER2 status was equivocal. Results: There were 439 consecutive stage I-III breast cancer patients, of which 271 (61.7%) were HR+/HER2-, 75 (17.1%) were HR+/HER2+, 30 (6.8%) were HR-/HER+ and 63 (14.4%) were HR-/HER2-. A total of 192 patients underwent neoadjuvant chemotherapy and the remaining 235 patients did not. Of these 235 patients, 204 underwent adjuvant chemotherapy. High serum HER2 levels (≥15 ng/ml) were reported in 51 patients (11.6%) and HER2-positive status in tumor tissue was observed in 105 patients (23.9%). High serum HER2 levels were significantly associated with tumor size > 2cm (p=0.032), high histologic grade (0.048), negative HR status and neoadjuvant chemotherapy usage. Patients who had high baseline serum HER2 levels had a worse disease free survival (DFS) (p Conclusions: This is the largest study in the evaluation of serum HER2 levels at diagnosis on the prognosis of patients with operable breast cancer. Our results showed that baseline serum HER2 level is a good prognostic marker in patients with operable breast cancer. High serum HER2 levels at diagnosis were associated with worse DFS, especially in patients of HR+/HER2-, HR+/HER2+ and HR-/HER2+ subtypes. Citation Format: Moo Hyun Lee, Siew Kuan Lim, Ji Young You, Eun Jin Song, So-Youn Jung, See Youn Lee, Han-Sung Kang, Eun Sook Lee. The significance of serum HER2 levels at diagnosis on outcome of breast cancer patients by molecular subtype [abstract]. In: Proceedings of the Thirty-Seventh Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2014 Dec 9-13; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2015;75(9 Suppl):Abstract nr P4-02-04.