Anthracycline-containing neoadjuvant chemotherapy (NACT) is the standard treatment for early triple-negative breast cancer (eTNBC); however, it is associated with substantial toxicity. We performed whole transcriptome profiling of baseline tumor biopsies to identify gene networks predictive and prognostic for pathological complete response (pCR) and survival after de-escalated, anthracycline-free NACT in the WSG-ADAPT-TN trial (NCT01815242). eTNBC patients (cT1c-cT4c, cN +) were randomized to 12 weeks of nab-paclitaxel + gemcitabine (n = 182) or nab-paclitaxel + carboplatin (n = 154). The primary endpoint was pCR (ypT0/is, ypN0), and the secondary endpoints included survival and translational research. AmpliSeq RNA sequencing, allowing simultaneous analysis of the expression of > 20,000 genes, was performed in 135 patients. Differentially expressed genes were evaluated in training (n = 67) and validation (n = 68) sets, and a polygenic score (PS) for prediction of pCR (PS:pCR) and a PS for prediction of invasive disease-free survival (PS:iDFS) were found. 49/135 (36.3

AbstractPurpose :Tamoxifen undergoes Patients and Methods :We conducted a prospective, interventional, three group randomized trial including 235 patients with hormone receptor–positive breast cancer who received standard tamoxifen therapy (20 mg/day). Patients were stratified by CYP2D6 genotype (n = 78), defining poor, intermediate, and normal metabolizers, or by baseline (Z)-endoxifen plasma concentration (n = 78), defining ≤n = 79) received placebo regardless of metabolizer phenotype. The primary endpoint was the number of patients with (Z)-endoxifen levels >32 nmol/L after 6 weeks of treatment. Adverse events were continuously monitored. Results: A higher proportion of patients in both intervention groups achieved target concentrations >32 nmol/L compared with control (P < 0.0001). At 3 mg (Z)-endoxifen supplementation, 92.3% of CYP2D6 poor metabolizer patients and all patients with baseline (Z)-endoxifen ≤15 nmol/L achieved the target concentration. At 1.5 mg (Z)-endoxifen supplementation, 88% of CYP2D6 intermediate metabolizer patients and 95% of patients with 15 to 25 nmol/L baseline (Z)-endoxifen levels achieved the target concentration. Similar proportions of patients receiving (Z)-endoxifen (6/80, 7.5%) or placebo (8/155, 5.2%) experienced grade 3 adverse events. Conclusions: Adding low-dose (Z)-endoxifen to standard tamoxifen is safe and provides a new approach to personalized antiestrogen treatment for patients with low endoxifen plasma levels.

Suppl Fig. S1: Concentration time course of tamoxifen, N-desmentyl tamoxifen, (Z)-4-hydroxy tamoxifen, and (Z)-endoxifen

Inter- and intra-assay variability

Representativeness of study participants

Endpoint analysis in PP-population

Suppl Fig S2: Concentration ratio (E)-endoxifen to (Z)-endoxifen

Abstract HER2DX genomic assay in triple-negative breast cancer (TNBC) patients treated with 12-weeks of neoadjuvant chemotherapy: a correlative analysis from WSG-ADAPT-TN phase II trial Background: Biomarkers for de-escalation and escalation of systemic therapy in early-stage TNBC are needed. HER2DX is a standardized prognostic (risk-score) and predictive (pathological complete response [pCR]-score) assay based on clinical and gene expression-based data. Here we aimed to test the value of HER2DX assay in early TNBC. Methods: Standardized HER2DX was evaluated centrally using RNA from baseline FFPE tumor biopsies from the WSG-ADAPT-TN study (NCT01815242), a multicenter phase II trial that randomized 336 patients with stage I–III early TNBC to 12-weeks of nab-paclitaxel 125 mg/m2 plus gemcitabine 1000 mg/m2 d1,8 every 3 weeks (arm A) versus nab-paclitaxel 125 mg/m2 plus carboplatin AUC2 day 1,8 every 3 weeks (arm B). The primary aim was to test the ability of HER2DX pCR and risk-score models to predict pCR (ypT0/isN0) and survival endpoints, respectively, such as invasive disease-free survival (iDFS), distant disease-free survival (DDFS) and overall survival (OS). Secondary objectives were to assess the association of the i) HER2DX immune signature score and ii) percentage (%) of stromal tumor infiltrating lymphocytes (sTILs) with efficacy endpoints. Uni- and multi-variable logistic regression and Cox models tested the association of each variable with each endpoint. Results: HER2DX was evaluated in 126 (37.5%) baseline pre-treatment tumors. Mean age was 52.1 (range 26-76). cT1 represented 40.5% of cases and 72.2% were cN0. Overall, pCR rate was 34.1% (95%CI 26.1 – 43.2) and median follow-up was 5.0 years. Median sTILs at baseline was 31.6% (range 0-90) and moderately correlated with the IGG signature (coefficient=0.57). The % of HER2DX high-, medium- and low-pCR groups was 41.3%, 47.6% and 11.1%, respectively. HER2DX pCR score (as a continuous variable) was significantly associated with pCR in univariate (odds ratio [OR per 10-unit increase]=1.31, 1.06-1.64, p=0.016) and after adjusting by treatment arm (OR=1.31, 1.06-1.65, p=0.015). Overall, the pCR rates in HER2DX pCR-high, -medium and -low groups were 46.2%, 26.7% and 21.4%, respectively (high vs medium/low OR=2.48, 1.17-5.34, p=0.018). In arm B (n=51), the pCR rates in HER2DX pCR-high, -medium and -low groups were 47.8%, 25.0% and 0.0% respectively (high vs medium/low OR=3.36, 1.02-12.0, p=0.051). In terms of the risk-score, the % of HER2DX low-risk and high-risk groups was 60.3% and 39.7%, respectively. HER2DX risk score as a continuous variable was significantly associated with iDFS, DDFS and OS (p< 0.001 in all univariate analysis), and after adjusting by variables such as arm and pCR status (all p< 0.05). sTILs were not associated with any survival endpoint (all p >0.35). The HER2DX immune signature was significantly associated with iDFS (p=0.012), DDFS (p=0.022) and OS (p=0.012). Conclusion: The HER2DX genomic test in TNBC provides valuable insights into the response and survival following neoadjuvant taxane-based chemotherapy in the absence of immunotherapy. The development of a tailored genomic assay for TNBC is currently in progress. Citation Format: Oleg Gluz, Fara Brasó-Maristany, Ulrike Nitz, Laia Paré, Matthias Christgen, Guillermo Villacampa, Benedetta Conte, Sherko Kuemmel, Ronald Kates, Cornelia Kolberg-Liedtke, Eva-Maria Grischke, Helmut Forstbauer, Michael Braun, Mathias Warm, John Hackmann, Christoph Uleer, Bahriye Aktas, Claudia Schumacher, Ana Vivancos, Rachel Wuerstlein, Joel S. Parker, Monika Graeser, Charles M. Perou, Christine zu Eulenburg, Patricia Villagrasa, Hans-Heinrich Kreipe, Aleix Prat, Nadia Harbeck. HER2DX genomic assay in triple-negative breast cancer (TNBC) patients treated with 12-weeks of neoadjuvant chemotherapy: a correlative analysis from WSG-ADAPT-TN phase II trial [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO2-15-07.

BACKGROUND:Breast cancer patients with residual disease after neoadjuvant systemic treatment (NAST) have a worse prognosis compared with those achieving a pathologic complete response (pCR). Earlier identification of these patients might allow timely, extended neoadjuvant treatment strategies. We explored the feasibility of a vacuum-assisted biopsy (VAB) after NAST to identify patients with residual disease (ypT+ or ypN+) prior to surgery.METHODS:We used data from a multicenter trial, collected at 21 study sites (NCT02948764). The trial included women with cT1-3, cN0/+ breast cancer undergoing routine post-neoadjuvant imaging (ultrasound, MRI, mammography) and VAB prior to surgery. We compared the findings of VAB and routine imaging with the histopathologic evaluation of the surgical specimen.RESULTS:Of 398 patients, 34 patients with missing ypN status and 127 patients with luminal tumors were excluded. Among the remaining 237 patients, tumor cells in the VAB indicated a surgical non-pCR in all patients (73/73, positive predictive value [PPV] 100%), whereas PPV of routine imaging after NAST was 56.0% (75/134). Sensitivity of the VAB was 72.3% (73/101), and 74.3% for sensitivity of imaging (75/101).CONCLUSION:Residual cancer found in a VAB specimen after NAST always corresponds to non-pCR. Residual cancer assumed on routine imaging after NAST corresponds to actual residual cancer in about half of patients. Response assessment by VAB is not safe for the exclusion of residual cancer. Response assessment by biopsies after NAST may allow studying the new concept of extended neoadjuvant treatment for patients with residual disease in future trials.

Supplementary Figure from De-escalated Neoadjuvant Chemotherapy in Early Triple-Negative Breast Cancer (TNBC): Impact of Molecular Markers and Final Survival Analysis of the WSG-ADAPT-TN Trial

PURPOSENeoadjuvant systemic treatment (NST) elicits a pathologic complete response in 40%-70% of women with breast cancer. These patients may not need surgery as all local tumor has already been eradicated by NST. However, nonsurgical approaches, including imaging or vacuum-assisted biopsy (VAB), were not able to accurately identify patients without residual cancer in the breast or axilla. We evaluated the feasibility of a machine learning algorithm (intelligent VAB) to identify exceptional responders to NST.METHODSWe trained, tested, and validated a machine learning algorithm using patient, imaging, tumor, and VAB variables to detect residual cancer after NST (ypT+ or in situ or ypN+) before surgery. We used data from 318 women with cT1-3, cN0 or +, human epidermal growth factor receptor 2–positive, triple-negative, or high-proliferative Luminal B–like breast cancer who underwent VAB before surgery (ClinicalTrials.gov identifier: NCT02948764 , RESPONDER trial). We used 10-fold cross-validation to train and test the algorithm, which was then externally validated using data of an independent trial (ClinicalTrials.gov identifier: NCT02575612 ). We compared findings with the histopathologic evaluation of the surgical specimen. We considered false-negative rate (FNR) and specificity to be the main outcomes.RESULTSIn the development set (n = 318) and external validation set (n = 45), the intelligent VAB showed an FNR of 0.0%-5.2%, a specificity of 37.5%-40.0%, and an area under the receiver operating characteristic curve of 0.91-0.92 to detect residual cancer (ypT+ or in situ or ypN+) after NST. Spiegelhalter's Z confirmed a well-calibrated model ( z score –0.746, P = .228). FNR of the intelligent VAB was lower compared with imaging after NST, VAB alone, or combinations of both.CONCLUSIONAn intelligent VAB algorithm can reliably exclude residual cancer after NST. The omission of breast and axillary surgery for these exceptional responders may be evaluated in future trials.

Importance Adjuvant denosumab might improve disease-free survival in hormone receptor (HR)–positive primary breast cancer (BC). The optimal neoadjuvant nab-paclitaxel schedule in terms of efficacy and safety is unclear. Objective To determine whether adding denosumab to anthracycline/taxane-containing neoadjuvant chemotherapy (NACT) increases the pathological complete response (pCR) rate and which nab-paclitaxel schedule is more effective in the NACT setting. Design, Setting, and Participants The GeparX was a multicenter, prospective, open-label, phase 2b, 2 × 2 randomized clinical trial conducted by GBG and AGO-B at 38 German sites between February 2017 and March 2019. The analysis data set was locked September 4, 2020; analysis was completed November 13, 2020. Patients had unilateral or bilateral primary BC, stage cT2-cT4a-d or cT1c, with either clinically node-positive or pathologically node-positive or HR-negative disease, or Ki-67 proliferation index greater than 20%, orERBB2(formerlyHER2)–positive BC. Interventions Patients were randomized to receive or not receive denosumab, 120 mg subcutaneously every 4 weeks for 6 cycles, and either nab-paclitaxel, 125 mg/m2weekly for 12 weeks or days 1 and 8 every 3 weeks for 4 cycles (8 doses), followed by 4 cycles of epirubicin/cyclophosphamide, 90/600 mg/m2(every 2 weeks or every 3 weeks). Carboplatin was given in triple-negative BC (TNBC), and trastuzumab biosimilar ABP980 plus pertuzumab was given inERBB2-positive BC (ERBB2-positive substudy). Main Outcomes and Measures The primary outcome was pCR rates between arms for each randomization. Results A total of 780 female (n = 779) and male (n = 1) patients (median [range] age, 49.0 [22-80] years) were randomized to the 4 treatment groups. The pCR (ypT0 ypN0) rate was 41.0% (90% CI, 37%-45%) with denosumab vs 42.8% (90% CI, 39%-47%) (P = .58) without denosumab, irrespective of BC subtype. Nab-paclitaxel weekly resulted in a significantly (significance level of α = .10) higher pCR rate of 44.9% (90% CI, 41%-49%) vs 39.0% (90% CI, 35%-43%) (P = .06) with nab-paclitaxel days 1 and 8 every 3 weeks. The pCR rates for nab-paclitaxel schedules in subgroups were only significantly different for TNBC (60.4% vs 50.0%;P = .06). Grade 3 to 4 toxic effects did not differ with or without denosumab. Nonhematologic toxic effects of grade 3 to 4 were higher with nab-paclitaxel weekly (33.7% vs 24.1%;P = .004). Conclusions and Relevance In this randomized clinical trial, denosumab added to anthracycline/taxane-based NACT did not improve pCR rates. Nab-paclitaxel at a dosage of 125 mg/m2weekly significantly increased the pCR rate compared with the days 1 and 8, every-3-weeks schedule overall and in TNBC, but generated higher toxicity. Trial Registration ClinicalTrials.gov Identifier:NCT02682693

Abstract Background Higher density of stromal tumor-infiltrating lymphocytes (sTILs) at baseline has been associated with increased rates of pathological complete response (pCR) after neoadjuvant chemotherapy (NACT) in triple-negative breast cancer (TNBC). While evidence supports favorable association of pCR with survival in TNBC, an independent impact of sTILs (after adjustment for pCR) on survival is not yet established. Moreover, the impact of sTIL dynamics during NACT on pCR and survival in TNBC is unknown. Methods The randomized WSG-ADAPT TN phase II trial compared efficacy of 12-week nab-paclitaxel with gemcitabine versus carboplatin. This preplanned translational analysis assessed impacts of sTIL measurements at baseline (sTIL-0) and after 3 weeks of chemotherapy (sTIL-3) on pCR and invasive disease-free survival (iDFS). Predictive performance of sTIL-0 and sTIL-3 for pCR was quantified by ROC analysis and logistic regression; Kaplan–Meier estimation and Cox regression (with mediation analysis) were used to determine their impact on iDFS. Results For prediction of pCR, the AUC statistics for sTIL-0 and sTIL-3 were 0.60 and 0.63, respectively, in all patients; AUC for sTIL-3 was higher in NP/G. The positive predictive value (PPV) of “lymphocyte-predominant” status (sTIL-0 ≥ 60%) at baseline was 59.3%, though only 13.0% of patients had this status. To predict non-pCR, the cut point sTIL-0 ≤ 10% yielded PPV = 69.5% while addressing 33.8% of patients. Higher sTIL levels (particularly at 3 weeks) were independently and favorably associated with better iDFS, even after adjusting for pCR. For example, the adjusted hazard ratio for 3-week sTILs ≥ 60% (vs. < 60%) was 0.48 [0.23–0.99]. Low cellularity in 3-week biopsies was the strongest individual predictor for pCR (in both therapy arms), but not for iDFS. Conclusion The independent impact of sTILs on iDFS suggests that favorable immune response can influence key tumor biological processes for long-term survival. The results suggest that the reliability of pCR following neoadjuvant therapy as a surrogate for survival could vary among subgroups in TNBC defined by immune response or other factors. Dynamic measurements of sTILs under NACT could support immune response-guided patient selection for individualized therapy approaches for both very low levels (more effective therapies) and very high levels (de-escalation concepts). Trial registration: Clinical trials No: NCT01815242, retrospectively registered January 25, 2013.

AbstractPurpose: Although optimal treatment in early triple-negative breast cancer (TNBC) remains unclear, de-escalated chemotherapy appears to be an option in selected patients within this aggressive subtype. Previous studies have identified several pro-immune factors as prognostic markers in TNBC, but their predictive impact regarding different chemotherapy strategies is still controversial. Experimental Design: ADAPT-TN is a randomized neoadjuvant multicenter phase II trial in early patients with TNBC (n = 336) who were randomized to 12 weeks of nab-paclitaxel 125 mg/m2 + gemcitabine or carboplatin d 1,8 q3w. Omission of further (neo-) adjuvant chemotherapy was allowed only in patients with pathological complete response [pCR, primary endpoint (ypT0/is, ypN0)]. Secondary invasive/distant disease-free and overall survival (i/dDFS, OS) and translational research objectives included quantification of a predictive impact of markers regarding selection for chemotherapy de-escalation, measured by gene expression of 119 genes (including PAM50 subtype) by nCounter platform and stromal tumor-infiltrating lymphocytes (sTIL). Results: After 60 months of median follow-up, 12-week-pCR was favorably associated (HR, 0.24; P = 0.001) with 5y-iDFS of 90.6% versus 62.8%. No survival advantage of carboplatin use was observed, despite a higher pCR rate [HR, 1.04; 95% confidence interval (CI), 0.68–1.59]. Additional anthracycline-containing chemotherapy was not associated with a significant iDFS advantage in pCR patients (HR, 1.29; 95% CI, 0.41–4.02). Beyond pCR rate, nodal status and high sTILs were independently associated with better iDFS, dDFS, and OS by multivariable analysis. Conclusions: Short de-escalated neoadjuvant taxane/platinum-based combination therapy appears to be a promising strategy in early TNBC for using pCR rate as an early decision point for further therapy (de-) escalation together with node-negative status and high sTILs. See related commentary by Sharma, p. 4840

Aim: To evaluate HER2-negative breast cancer (BC) with a low hormone receptor (HR) expression, with regard to pathological complete response (pCR) and survival, in comparison to triple-negative BC (TNBC) and strong HR-positive BC. Methods: We compared negative [oestrogen (ER) and progesterone receptor (PR) <1%], low positive (ER and/or PR 1-9%) and strong-positive (ER or PR 10-100%) HR-expression in neoadjuvant clinical trial cohorts (n = 2765) of BC patients. End-points were disease-free survival (DFS), distant-disease free survival (DDFS) and overall survival (OS). We performed RNA sequencing on available tumour tissue samples from patients with low-HR expression (n = 38). Results: Ninety-four (3.4%) patients had low HR-positive tumours, 1769 (64.0%) had strong HR-positive tumours, and 902 (32.6%) had TNBC. There were no significant differences in pCR rates between women with low HR-positive tumours (27.7%) and women with TNBC (35.5%). DFS and DDFS were also not different [for DFS, hazard ratio 1.26, 95%-CI (confidence interval) : 0.87-1.83, log-rank test p = 0.951; for DDFS, hazard ratio 1.17, 95%-CI: 0.78-1.76, log-rank test p = 0.774]. Patients with strong HR-positive tumours had a significantly lower pCR rate (pCR 9.4%; odds ratio 0.38, 95%-CI: 0.23-0.63), but better DFS (hazard ratio 0.48, 95%-CI: 0.33-0.70) and DDFS (hazard ratio 0.49, 95%-CI: 0.33-0.74) than patients with low HR-positive tumours. Molecular subtyping (RNA sequencing) of low HR-positive tumours classified these predominantly into a basal subtype (86.8%). Conclusion: Low HR-positive, HER2-negative tumours have a similar clinical behaviour to TNBC showing high pCR rates and poor survival and also a basal-like gene expression signature. Patients with low HR-positive tumours should be regarded as candidates for therapy strategies targeting TNBC. ? 2021 Elsevier Ltd. All rights reserved.

Background The association of early changes in the immune infiltrate during neoadjuvant chemotherapy (NACT) with pathological complete response (pCR) in triple-negative breast cancer (TNBC) remains unexplored. Methods Multiplexed immunohistochemistry was performed in matched tumor biopsies obtained at baseline and after 3 weeks of NACT from 66 patients from the West German Study Group Adjuvant Dynamic Marker-Adjusted Personalized Therapy Trial Optimizing Risk Assessment and Therapy Response Prediction in Early Breast Cancer - Triple Negative Breast Cancer (WSG-ADAPT-TN) trial. Association between CD4, CD8, CD73, T cells, PD1-positive CD4 and CD8 cells, and PDL1 levels in stroma and/or tumor at baseline, week 3 and 3-week change with pCR was evaluated with univariable logistic regression. Results Compared with no change in immune cell composition and functional markers, transition from 'cold' to 'hot' (below-median and above-median marker level at baseline, respectively) suggested higher pCR rates for PD1-positive CD4 (tumor: OR=1.55, 95% CI 0.45 to 5.42; stroma: OR=2.65, 95% CI 0.65 to 10.71) and PD1-positive CD8 infiltrates (tumor: OR=1.77, 95% CI 0.60 to 5.20; stroma: OR=1.25, 95% CI 0.41 to 3.84; tumor+stroma: OR=1.62, 95% CI 0.51 to 5.12). No pCR was observed after 'hot-to-cold' transition in PD1-positive CD8 cells. pCR rates appeared lower after hot-to-cold transitions in T cells (tumor: OR=0.26, 95% CI 0.03 to 2.34; stroma: OR=0.35, 95% CI 0.04 to 3.25; tumor+stroma: OR=0.00, 95% CI 0.00 to 1.04) and PD1-positive CD4 cells (tumor: OR=0.60, 95% CI 0.11 to 3.35; stroma: OR=0.22, 95% CI 0.03 to 1.92; tumor+stroma: OR=0.32, 95% CI 0.04 to 2.94). Higher pCR rates collated with 'altered' distribution (levels below-median and above-median in tumor and stroma, respectively) of T cell (OR=3.50, 95% CI 0.84 to 14.56) and PD1-positive CD4 cells (OR=4.50, 95% CI 1.01 to 20.14). Conclusion Our exploratory findings indicate that comprehensive analysis of early immune infiltrate dynamics complements currently investigated predictive markers for pCR and may have a potential to improve guidance for individualized de-escalation/escalation strategies in TNBC.

Abstract Background: Among patients with highly heterogeneous HER2+ breast cancer (BC), pathological complete response (pCR) (ypT0/is/ypN0) is associated with improved prognosis. The prospective, phase-II neoadjuvant 3-arm WSG HER2+/HR+ trial (ADAPT-TP) showed pCR rates of about 41.0% after 4xT-DM1+/-ET and 15% after trastuzumab+ET. Pre-planned translational analysis of ADAPT-TP has revealed several biomarkers with impact on pCR, such as PIK3CA mutation status, HER2-enriched subtype (by PAM50), Bcl-2 and most notably immune biomarkers (e.g.CD8/tumor center). In particular, higher CD8 protein expression values either at baseline and/or after one cycle (3w) of neoadjuvant therapy were favorable for pCR. Moreover, CD8 and PDL1 dynamics were indicators of early therapy response, and dynamical response was itself favorable for pCR. The impact of immune biomarkers suggests that tumor infiltrating lymphocytes (TILs) could serve as predictive markers for de-escalated anti-HER2 therapy, in particular T-DM1. Methods: Semi-quantitative, triplicate TIL measurements were performed in tissue obtained at baseline (TIL-0) and at 3 weeks (TIL-3). At each timepoint, the median of the three measurements was used for analysis. CD8 and PD-L1 expression measurements were obtained by mRNA at baseline at both time points by immunohistochemistry (IHC). Associations of semiquantitative TIL-0/TIL-3 levels with pCR and with other clinical/pathological measurements were analyzed using logistic regression, rank correlations, t and chi-square statistics. Results: TIL-0 and TIL-3 were available in 355/375 and 301/375 randomized patients, respectively. Associations of TIL-0, TIL-3 and TIL-dynamics (increase from TIL-0 to TIL-3) with CD8 and PD-L1 (including dynamics) and with clinical factors (tumor size, nodal status, ER and PR status, grade, patient age, Ki67 and menopausal status) revealed several prominent relationships: Both TIL-0 and TIL-3 were at least moderately correlated with IHC measurements of CD8 (at center, not at invasive margin) and of PD-L1 at both timepoints. At cycle 2, the correlation of TILs and CD8 was strong, particularly in the T-DM1 arms (r=.7, p<.001). CD8 by mRNA was moderately correlated with TIL-0. Correlations between clinical factors and TILs at both timepoints were weak. These associations with known factors influencing pCR suggest a possible direct association of TILs with pCR; logistic regression using standardized TIL-0 revealed a modest (standardized) odds ratio of about 1.4 for pCR for TIL-0 in the T-DM1 arms, though not in the whole cohort. In particular, patients receiving T-DM1 with TIL0≥40% (about 8%) had pCR of 70% vs. 40% pCR for others (p=.016). We observed a dynamic increase of TILs during T-DM1 treatment of about 10 percentage points. However, neither these dynamics nor TIL-3 were significantly associated with pCR (in contrast to CD8 protein expression at cycle 2). Interpretation: To the best of our best knowledge, these are the first prospective data regarding the predictive value of TILs and TIL dynamics in HR+/HER2+ BC treated with de-escalated anti-HER2 therapy. Very high TIL levels (>40%) were associated with an excellent pCR rate of 70% in TDM1treated patients. However, CD8 expression and dynamics of CD8 were more strongly predictive for efficacy of de-escalated treatment than TILs – despite promising data on baseline and/or on-treatment TILs as markers for improved prognosis and higher sensitivity to (dual) anti-HER2 blockade (with or without chemotherapy) in unselected HER2+ BC. Further research on static and dynamic immune markers (according to HR+ and HR-/HER2+ subtypes) is needed prior to final conclusions regarding the clinical impact of TILs in early HER2+ BC. Citation Format: Claudia Biehl, Cornelia Kolberg-Liedtke, Oleg Gluz, Friedrich Feuerhake, Matthias Christgen, Ronald Kates, Eva-Maria Grischke, Helmut Forstbauer, Michael Braun, Mathias Warm, John Hackmann, Christoph Uleer, Bahriye Aktas, Claudia Schumacher, Sherko Kuemmel, Sanne L de Haas, Regula Deurloo, Rachel Wuerstlein, Ulrike Nitz, Hans H. Kreipe, Nadia Harbeck, West German Study Group. Impact of immune markers on response to neoadjuvant de-escalated T-DM1 or trastuzumab with/or without endocrine therapy in HR+/HER2+ early breast cancer: A translational subproject of the WSG-ADAPT-HER2+/HR+ trial [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr PD5-10.

Objective: We evaluated the ability of minimally invasive, image-guided vacuum-assisted biopsy (VAB) to reliably diagnose a pathologic complete response in the breast (pCR-B). Summary Background Data: Neoadjuvant systemic treatment (NST) elicits a pathologic complete response in up to 80% of women with breast cancer. In such cases, breast surgery, the gold standard for confirming pCR-B, may be considered overtreatment. Methods: This multicenter, prospective trial enrolled 452 women presenting with initial stage 1-3 breast cancer of all biological subtypes. Fifty-four women dropped out; 398 were included in the full analysis. All participants had an imaging-confirmed partial or complete response to NST and underwent study-specific image-guided VAB before guideline-adherent breast surgery. The primary endpoint was the false-negative rate (FNR) of VAB-confirmed pCR-B. Results: Image-guided VAB alone did not detect surgically confirmed residual tumor in 37 of 208 women [FNR, 17.8%; 95% confidence interval (CI), 12.8–23.7%]. Of these 37 women, 12 (32.4%) had residual DCIS only, 20 (54.1%) had minimal residual tumor (<5 mm), and 19 of 25 (76.0%) exhibited invasive cancer cellularity of ≤10%. In 19 of the 37 cases (51.4%), the false-negative result was potentially avoidable. Exploratory analysis showed that performing VAB with the largest needle by volume (7-gauge) resulted in no false-negative results and that combining imaging and image-guided VAB into a single diagnostic test lowered the FNR to 6.2% (95% CI, 3.4%–10.5%). Conclusions: Image-guided VAB missed residual disease more often than expected. Refinements in procedure and patient selection seem possible and necessary before omitting breast surgery.