Thompson, E Aubrey

1591 Background: The 21-gene OncotypeDX (ODX) recurrence score (RS) is the standard for chemotherapy decision-making in HR+/HER2- early breast cancer (EBC), but cost limits accessibility in resource-constrained settings. The Magee equations (MEs) use routine pathology features (Nottingham grade and IHC; ER/PR/HER2/Ki-67) to estimate RS. We performed a meta-analysis to validate MEs performance as a triage tool for ODX testing and a qualitative synthesis to identify sources of discordance, highlighting the transition toward objective digital pathology AI models. Methods: A systematic review identified validation studies comparing MEs with RS in HR+ EBC. Studies with sufficient data to construct a 2X2 contingency table were included; neoadjuvant trials were excluded. Primary outcomes were Negative Predictive Value (NPV) for identifying low-risk cases (RS <26 for the current TAILORx cutoff and RS<31 for the historical cutoff) and ODX test sparing rate (TSR). Data were pooled using random-effects models. Qualitative themes regarding interpretation variability were extracted from study results and discussion sections. Results: Thirteen studies met the inclusion criteria, representing 5396 patients in global cohorts from the USA, Mexico, Colombia, Jordan, France, Belgium, and Canada. For RS >26, Magee <18 achieved pooled NPV of 0.96 (95% CI: 0.94-0.97) and TSR 61% (95% CI:51%-69%). For RS >31, NPV increased to 0.99 (95% CI: 0.97-1.00) and TSR 52% (95% CI: 44%-59%). Pooled diagnostic performance for Magee <18 predicting RS <26 demonstrated 83% sensitivity and 71% specificity (AUC 0.81, LR+:2.53, LR-:0.28). Qualitative analysis of discordance identified: (1) Inter-observer variability: Nottingham mitotic counts and Ki-67 scoring were the primary drivers of score fluctuations. (2) IHC quantification: Variations in H-score calculation and Allred-to-H-score conversion introduced heterogeneity (3) Pre-analytical and biological factors: Inflammation and stromal proliferation occasionally inflated genomic RS; selection of non-representative blocks and intratumor heterogeneity further contributed to discordance (4) Technological solutions: Digital pathology and AI models emerge as solutions to standardize these variables. Conclusions: Magee-based triage provides a safe and cost-effective strategy for HR+ EBC risk stratification, with NPV up to 99% for excluding high-risk disease and sparing up to 61% of ODX testing. These results confirm a robust histopathological signal. Transitioning to objective digital pathomics provides a pathway to reduce manual subjectivity and democratize precision oncology globally. Pooled diagnostic accuracy of Magee equations by cutoff. Magee score and RS cutoff Number of studies Total patients Pooled NPV (95% CI) ODX test sparing rate (95% CI) Magee <18/ RS>26 8 4153 0.96 (0.94-0.97) 61% (51%-69%) Magee <18/ RS>31 5 1243 0.99 (0.97-1.00) 52% (44%-59%)

Abstract Background The incidence of early onset breast cancers (BCs) has increased, paralleling rising trends in delayed childbearing. We hypothesize that a distinct postpartum BC (PPBC) subtype, identifiable by time since last birth (TSLB) and biomarker expression, contributes to this trend. Methods We applied GeoMx Digital Spatial Profiling (DSP) to measure associations between TSLB and 71 proteins in 640 BCs from women aged ≤40 years included in the Young Women’s Breast Cancer Study. We analyzed data using univariable linear regression and multivariable sliced inverse regression to account for higher order interactions among biomarkers. Results In keratin-rich segments, progesterone receptor (PR) (P = 1.00 × 10−4) and PTEN (P = 1.00 × 10−3) were associated with longer TSLB; multivariable analyses revealed positive associations for GZMB (P = 4.00 × 10−4), SMA (P = 1.00 × 10−4), and NF-1 (P = 1.00 × 10−3). In keratin-poor segments, univariable significant positive associations were found for PR (P = 2.00 × 10−4) and PTEN (P = 1.00 × 10−3), whereas CD20 (P = 3.00 × 10−4) and CTLA4 (P = 4.00 × 10−5) were negatively associated; multivariable significant associations were found for fibronectin (P = 3.00 × 10−5) and pan-Akt (P = 1.00 × 10−3). Associations persisted after adjustment for multiple comparisons and BC molecular subtypes. Associations including for PR, PTEN, and CD20 were strongest among women with the shortest TSLB. OPAL multiplex immunofluorescence assays for PR, PTEN, CD20, SMA, and CTLA4 replicated several DSP findings, particularly when stratified by subtype and with compartment matching. In TCGA, RNA species linked to proteins associated with TSLB correlated strongly with a T-cell exhaustion signature previously linked to poor prognosis among premenopausal women. Conclusion These data support PPBC as a biologically coherent phenotype defined by TSLB and biomarker profile, with potential implications for prevention and therapy.