Data extractionįor each selected manuscript, the following information was recorded by two independent reviewers: primary author name, year of publication, sample size, duration of follow-up, definition of pCR, patient and tumor characteristics, neoadjuvant regimen, adjuvant regimen if applicable, number of patients achieving a pCR, and number of outcome events by pCR status. Furthermore, only those publications where individual patient-level data were extractable either in the form of Kaplan–Meier (KM) curves with event data and/or survival estimates (e.g., median survival, and/or another landmark event such as 5-year survival with event data) were included. Studies were excluded from subanalyses based on receptor subtypes if HER2 status was unknown. Endocrine therapy–based neoadjuvant studies and neoadjuvant studies with radiation were also excluded. Studies including any neoplasm other than female breast cancer were excluded, as well as studies analyzing unresectable or metastatic breast cancer. Publications were included regardless of neoadjuvant regimen received. Inclusion criteria were clinical trials, prospective cohort studies, or retrospective cohort studies that reported pCR results after neoadjuvant chemotherapy as well as breast cancer recurrence and/or survival stratified by the presence or absence of pCR, with a total sample size of 25 patients or greater. 6), but is less understood for hormone receptor–positive (HR +)/HER2 − breast cancer, where pCR is less common and adjuvant endocrine therapy is the mainstay of systemic therapy. The association of pCR with improved long-term outcomes is recognized for HER2-positive (HER2 +) breast cancer and triple-negative (TN) breast cancer (TNBC ref. In addition, clinical subtype of breast cancer is an important factor to consider given differences in tumor biology as well as targeted therapy usage. Furthermore, these studies did not evaluate the impact of pCR on the utility of adjuvant therapy, which could potentially influence the clinical outcomes in patients with localized breast cancer. However, most neoadjuvant trials are powered to detect a difference in pCR among regimens, and likewise are not powered for long-term outcomes. Similarly, a meta-regression of 29 randomized prospective studies of NAT demonstrated pCR to be a strong prognostic factor, but the magnitude of relationship between pCR and EFS varied by type of NAT ( 5). In a pooled analysis of 12 clinical trials by Cortazar and colleagues, the authors demonstrated that pCR is associated with improved event-free survival (EFS), but the association between the magnitude of treatment-induced pCR change and corresponding improvement in EFS could not be established (i.e., delta pCR and delta EFS ref. While pCR demonstrates sensitivity to agents received in the neoadjuvant setting, true demonstration of treatment efficacy is dependent on its ability to predict long-term outcomes of recurrence and death, and this issue has not been completely settled in the literature. Yet, the prognostic significance of pCR after neoadjuvant chemotherapy remains somewhat controversial.
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