Abstract P4-06-06: Role of lymphatic SEC62 expression in prediction of treatment response in patients undergoing neoadjuvant chemotherapy for primary breast cancer

Abstract Background Chromosome 3q26 amplifications have been shown to represent a frequent alteration in various cancer entities including breast cancer. SEC62 - a 3q26 encoded gene - was identified as a potential onco- and tumor-driver gene for the pathogenesis of breast cancer. Sec62 seems to induce an increased stress tolerance, enhanced cell migration and proliferation in SEC62 overexpressing cells. Patients with SEC62 overexpressing breast cancer have been shown to have a higher rate of lymph node metastasis and poorer overall prognosis. Hence, we aspired to further evaluate the function of lymphatic SEC62 expression and its predictive role on the response to neoadjuvant chemotherapy. Objectives We aimed to assess the role of lymph node SEC62 expression as a predictive biomarker for response to neoadjuvant chemotherapy, besides we sought to evaluate potential differences in SEC62 expression levels in metastatic lymph node core biopsies and final pathology specimen according to breast cancer subtype. Material & Methods All nodal positive patients treated for primary breast cancer with neoadjuvant chemotherapy at the Department of Gynaecology and Obstetricts, Saarland University Hospital, Homburg, Germany between 01/2009 and 12/2019 were enrolled in this retrospective study. We analyzed SEC62 expression in tissue samples by immunohistochemistry (IHC). Sec62 immunoreactivity was evaluated using the immunoreactive score (IRS) according to Remmele and Stegner (0-12). For the assessment of the Sec62 protein content of the tumor cells, we rated Sec62 “low” for a score of 0-8, and “high” for 9-12 as described in previous publications. IHC was performed on initial lymph node core biopsy (CB) tissue (pre-treatment) or sentinel node biopsy specimen and on definite pathology specimen (PS) obtained during axillary dissection after completion of neoadjuvant chemotherapy.SEC62 expressions in both samples were compared and correlated with response to neoadjuvant chemotherapy, evaluated pathologically using the semi-quantitative response to neoadjuvant chemotherapy scoring system by Sinn et al. ranging from 0 (no effect) to 4 (no tumor detectable). Results 103 patients were assessed for eligibility. 15 cases were excluded, due to incomplete clinical information or insufficient slide quality, leaving 88 patients for final analysis. Median patient age was 55 (32-78) years and median response to neoadjuvant chemotherapy score of 2 (0-4). 11 (12.5%) patients had luminal A, 31 (35.2%) luminal B, 21 (23.9%) Her2/neu positive and 25 (28.4%) triple negative breast cancer. Median SEC62 expression in lymph node core biopsies was significantly higher compared to expression in final specimen (p<0.01). While no differences in basic expression of SEC62 in CB and the response to neoadjuvant chemotherapy were detected, patients with an IRS score ≤ 8 in PS and patients with a difference of IRS score ≥6 between CB and PS showed a significantly higher median response to neoadjuvant chemotherapy score compared to other patients (p< 0.01). Analyzing median Sec62 IHC expression in final pathology specimen, we observed significantly lower Sec62 scores for Her2/neu positive and triple negative patients compared to other subtypes (p<0.01). Median SEC62 expression showed the highest decrease between CB and PS in Her2/neu positive and triple negative patients. Regarding response to neoadjuvant chemotherapy, the effects described above could be observed in all breast cancer subtypes, but were strongest in triple negative patients. Conclusion We identified lymph node SEC62 expression as a promising biomarker for prediction of response to neoadjuvant chemotherapy in breast cancer patients. This effect seems to be strongest in patients with triple negative breast cancer. Citation Format: Julia Zimmermann, Anna Jung, Merle Doerk, Mariz Kasoha, Barbara Linxweiler, Maximilian Linxweiler, Mathias Wagner, Rainer Bohle, Marc Radosa, Erich Solomayer, Julia C Radosa. Role of lymphatic SEC62 expression in prediction of treatment response in patients undergoing neoadjuvant chemotherapy for primary breast cancer [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P4-06-06.