Abstract PS2-34: Concordance of breast cancer biomarker testing in core-needle biopsy and surgical specimens: A single institution experience
Authors: Slostad Jessica Anne , Yun Nicole , Schad Aimee , Warrior Surbhi , Rao Ruta 
Published: February 2021

Abstract
Accurate diagnostic biomarker testing, including estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor 2 (Her2) expression profile, is crucial to appropriate management decisions in breast cancer. Receptor status testing is typically performed on the initial core needle biopsy (CNB) and surgical specimen (SS). The rate of concordance between CNB and SS is unclear as is the impact this has on clinical decision making. The current guidelines on retesting are vague, which results in individual institutions and providers determining retesting policies. Several studies worldwide have assessed the concordance of receptor testing with mixed conclusions. We aim to determine concordance between CNB and SS, and whether this leads to clinically relevant management changes. A retrospective analysis was performed on patients with invasive breast cancer with available CNB and SS pathology at our institution between January 2010- May 2020. Patients who were treated with primary surgical resection and neoadjuvant chemotherapy with residual disease were included. Concordance rates between CNB and SS were assessed for ER, PR, and Her2 IHC/ FISH amplification. ER and PR status were defined per NCCN guidelines as “positive,” “low-positive (ER)” or “negative.” Major discrepancy was defined as a change in label of “positive” or “negative”. Minor discrepancy was defined as change &gt;10% without a “positive” or “negative” label change. Major discordance in Her2 was defined as change in label of “positive” or “negative” based on IHC or FISH amplification results. A minor discrepancy was a change in Her2 IHC (0-3) or FISH amplification without change in label of “positive” or “negative.” The clinical impact of discordant results was determined by investigator review. 748 patients met the eligibility criteria, and 64 of these patients received neoadjuvant therapy. For ER, there was 90.6% concordance, 2.2% major discordance, and 7.8% minor discordance between CNB and SS. For PR, there was 59.64% concordance, 11.9% major discordance, and 28.46% minor discordance. For Her2, there was 54.7% concordance, 1.6% major discordance, and 43.8% minor discordance. Of major discordance, ER (43.8%) led to the most change in management compared to Her2 and PR (12.5% and 2.2%, respectively). Retesting Her2 on SS did not change management when initial CNB was Her2 positive. For major discrepancies, patient demographics, tumor characteristics, treatment course, recurrence, and survival were reviewed. Although discordance was more common in PR and Her2 than ER biomarker profiles, major discordance leading to treatment changes were more common in ER and Her2. Retesting ER and Her2 on CNB and SS may be more clinically beneficial than retesting PR. Guidelines for retesting receptor profiles on CNB and SS are needed to best guide patient care management decisions that maximize clinical benefits while minimizing healthcare costs.
Table: Concordance of ER, PR, and HER2 Expression ProfileConcordanceMajor DiscrepancyMinor Discrepancy# Patients with Change in Treatment with Major DiscrepanciesER90.6%2.2%7.8%7/16 (43.8%)PR59.6%11.9%28.5%2/90 (2.2%)Her254.7%1.6%43.8%5/12 (12.5%)
Citation Format: Jessica Anne Slostad, Nicole Yun, Aimee Schad, Surbhi Warrior, Ruta Rao. Concordance of breast cancer biomarker testing in core-needle biopsy and surgical specimens: A single institution experience [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PS2-34.