Towards omitting breast cancer surgery in select patient groups: Assessment of pathologic complete response after neoadjuvant systemic therapy using biopsies—The MICRA trial.

Abstract

TPS593 Background: Improvements in systemic treatments for breast cancer patients has led to increasing rates of pathologic complete response (pCR). In addition, the identification of a pCR has been greatly improved with magnetic resonance imaging (MRI). In patients with a pCR, surgical resection of (part of) the original tumor area is performed to confirm the absence or presence of pCR and is not likely to contribute to locoregional control. With the MICRA trial (Minimally Invasive Complete Response Assessment) we aim to omit breast surgery in breast cancer patients achieving pathologic complete response (pCR) after neoadjuvant systemic therapy (NST) using biopsies, thus preventing overtreatment and improving quality of life. Methods: The MICRA trial is a multi-center observational prospective cohort study. In all breast cancer patients receiving NST, a marker is placed in the center of the tumor area before NST. 440 patients with radiologic complete response or partial response (0.1-2.0 cm residual contrast enhancement, ≥30% decrease in tumor size according to RECIST criteria) on contrast enhanced MRI will be included in the MICRA trial. Patients with hormone receptor positive, triple negative and Human Epidermal growth factor Receptor 2 tumors are eligible. After NST, 8 ultrasound-guided biopsies are obtained in the region surrounding the marker, while the patient is under general anesthesia. Immediately hereafter, breast surgery is performed and pathology results of the biopsies and resected specimens are compared. The primary endpoint is specificity of post-NST biopsies. In addition, sensitivity and positive and negative predictive value will be calculated. We will perform a multivariable analysis using data on MRI and ultrasound findings, pre-NST pathology parameters and post-NST biopsy results to determine what the most reliable method is to assess pCR and how many biopsies are needed for this purpose. Conclusion: With the MICRA-trial we aim to select a group of breast cancer patients in whom surgery of the breast after NST can be omitted, by predicting the presence of a pCR on biopsies. Clinical trial information: NTR6120.