Statistical analysis
RS
REGRESSION, DISSECTION, EVENT
Prior to combining the patients from each study into one analysis cohort, comparisons of the VCU and Emory patients were performed to assess whether the groups were similar enough for pooling. Due to small sample sizes, we were limited to conducting a simple descriptive exploration of study differences. Comparisons of continuous variables (age, RS result, chemotherapy cycles, months of endocrine therapy) were performed using the Wilcoxon Median 2-sample test, and categorical variables (race, ethnicity, menopausal status, nodal stage, HR status, grade, RS group, randomized neoadjuvant treatment group, cCR, cPR, and pCR) were evaluated using the Chi-square test or Fisher’s exact test for cell counts < 5. Comparisons could not be made by overall clinical stage, as this variable was not reported from VCU.No clinically significant differences were identified that would limit pooling of the study data. Although event counts were too low to perform robust regression models predicting study outcomes, associations between RS result, type of neoadjuvant therapy (comparing all RS groups), and pCR in the breast, lymph nodes and breast plus lymph nodes were evaluated using Fisher’s exact test. Of note, one patient who did not receive Sentinel Lymph Node Biopsy (SLNB) or Axillary Lymph Node Dissection (ALND) was excluded from the denominator for pCR Nodes.A sensitivity analysis was performed to assess the impact of the differing RS result cut-points in groups B and C between the studies on the outcomes. In this analysis, Emory patients with RS result = 25 were reassigned from Group D into Group C, since they were treated with neoadjuvant chemotherapy. Analyses were performed using SAS version 9.4 (SAS Institute, Cary, NC).Both studies were designed as pilot studies to assess feasibility and subsequently, there were no pre-planned power and sample size estimates performed in the combined analysis. Post hoc power calculations are controversial and of limited utility.