Assessment of ER, PR and HER2 on cell blocks and core needle biopsies in metastatic breast cancer: a real-world experience.

Introduction: The status of estrogen receptor (ER), progesterone receptor (PR) and human epidermal growth factor receptor 2 (HER2) plays a crucial role in the management of patients with metastatic breast cancer. Herein we report our experience on ER, PR and HER2 immunostains on cell block and core needle biopsy (CNB) specimens of metastatic breast cancers.

Methods: Cytological samples of metastatic breast cancer with associated cell blocks or core needle biopsies were identified on which ER, PR, or HER2 were ordered from 2019 to 2021. Both fine needle aspiration specimens and body effusion fluids were included. Patients' demographics, cancer histological subtype, biopsy site, specimen type (cell block or CNB) for immunohistochemistry and ER, PR and HER2 expression were recorded.

Results: 192 specimens from 177 patients were identified. Patients' mean age was 58.5 years (range 24-96). The majority of samples were obtained from patients with invasive ductal carcinoma. Staining was performed on core biopsies (n=74/192, 38.5%) and on cell blocks (n=118/192, 61.5%). Pleural fluid (n=75) was the most commonly sampled site followed by the liver (n=48) and lymph nodes (n=44). ER, PR and HER2 were positive in 76.3%, 79.3% and 13.2% of samples, respectively. Concordantly, ER+PR+HER2- was the most common sample phenotype. Seven samples had insufficient tissue to evaluate ER, PR or HER2 status.

Conclusion: ER, PR and HER2 immunohistochemical staining can be performed on cell block or CNB specimens of metastatic breast cancer and can provide reliable information to clinicians for optimal patient care. .