Who Are Suitable Patients for Omitting Breast Surgery as an Exceptional Responder in Selected Molecular Subtypes of Breast Cancer After Neoadjuvant Systemic Treatment?

<i>Background and Objectives</i>: Among breast cancer molecular types, HER2 positive and triple negative (TN) subtypes have the highest likelihood of pathological complete response (pCR), which is a surrogate marker for reduced recurrence and improved patient survival after neoadjuvant systemic treatment (NST). Preoperative pathological identification of these exceptional responders is a new era. Therefore, we aimed to determine the accuracy of trucut biopsy in identifying the exceptional responders in selected molecular subtypes of breast cancer patients. <i>Materials and Methods</i>: This two-centre, observational, single-arm, prospective, pilot study was conducted between January and September 2024. The patients with TN or HER2 positive breast cancer whose breast tumour had completely disappeared on the radiological assessment including MRI after neoadjuvant therapy were enrolled. To assess neoadjuvant treatment response, a standardised biopsy protocol was used, consisting of 10 samples from the marked tumour area per patient by 12 G core needle. Then, all patients underwent surgery. The pathological results of both postchemo-presurgical biopsy and surgical breast specimen were compared. <i>Results</i>: The study included 20 patients. The mean age of the patients was 47.3 years. The median tumour size at diagnosis was 23.1 mm. All biopsy results were concordant with the findings of surgical specimen. Seventeen patients had a complete response. The remaining 3 patients had residual disease. <i>Conclusions</i>: Along with thorough patient selection, post-chemo radiological assessment and the reliable biopsy technique are the key points in accurately predicting response to neoadjuvant treatment. If an image-guided core biopsy confirms elimination of tumour tissue at the marked tumour area with a radiological complete response on MRI after NST in breast cancer patients with selected molecular subtypes, these may be suitable patients as exceptional responders in whom we can omit breast surgery.