Breast surgery after neoadjuvant systemic therapy.

For patients with operable breast cancer, neoadjuvant systemic therapy (NST) can be used to downstage the primary tumor in the breast and to facilitate breast-conserving surgery (BCS) in patients with large tumors who desire breast conservation. Rates of breast pathologic complete response (pCR) after neoadjuvant chemotherapy (NAC) are highest in patients with triple-negative and human epidermal growth factor receptor 2 (HER2) positive (HER2⁺) disease; however, achieving pCR is not necessary for successful downstaging and avoidance of mastectomy, and rates of conversion to BCS-eligibility are high across all receptor subtypes. Neoadjuvant endocrine therapy (NET) can be used instead of NAC in postmenopausal patients with hormone receptor positive (HR⁺)/HER2 negative (HER2^-) breast cancer to downstage the breast, particularly when the patient has no clear indication for systemic chemotherapy, but desires breast conservation. In patients treated with NET, rates of conversion to BCS-eligibility are similar to rates observed with NAC. The oncologic safety of BCS after NAC and NET has been established in prospective trials, and local recurrence (LR) rates are acceptably low provided negative surgical margins can be obtained. Investigation is under way to determine the feasibility and safety of omitting breast surgery in patients with responsive subtypes who have no residual invasive or in situ disease identified on post-treatment tumor bed biopsies; however, the significant risk of missing residual disease-which may impact selection of adjuvant systemic therapy-may preclude future adoption of this approach.