Tenner, Kathleen

Abstract Purpose: Activation of the RAS/MAPK pathway is associated with reduced tumor-infiltrating lymphocytes and poor outcomes in triple-negative breast cancer. Previous studies demonstrated that inhibition of the MAPK pathway with a MEK inhibitor is synergistic with immune checkpoint inhibitors. Patients and Methods: We conducted a phase I/II trial of pembrolizumab and binimetinib in patients with metastatic triple-negative breast cancer with ≤3 prior lines of therapy. There were two dose levels (DL) with binimetinib at 45 mg at DL 0 and 30 mg at DL −1. Results: The recommended phase II dose was the standard dose of pembrolizumab with binimetinib 30 mg twice daily. The objective response rate (ORR) was 30.4%, with a numerically higher ORR in patients without liver metastasis at 45.5%. Among patients who achieved objective responses, 80% had a duration of response >12 months and ongoing even after stopping treatment (5.4–69.0 months). Patients with PD-L1–positive tumors (modified proportion score ≥10) were more likely to respond with an ORR of 66.7%. However, clinical benefit was observed in 25% of patients with PD-L1–negative tumors. Consistent with preclinical studies, four of six patients with clinical benefit had either increased PD-L1 or decreased p-ERK expressions in serial circulating cancer-associated macrophage-like cells after starting binimetinib. Conclusions: Pembrolizumab and binimetinib at 30 mg are safe with manageable toxicities. Promising activity was observed in patients without liver metastases. Future larger clinical trials are warranted to further evaluate the efficacy of this chemotherapy-free combination.

Abstract Background: Activation of the RAS/MAPK pathway is associated with reduced tumor-infiltrating lymphocytes and poor outcomes in triple-negative breast cancer (TNBC). This trial evaluated the efficacy of pembrolizumab in combination with binimetinib, a MEK inhibitor. Methods: Patients with unresectable locally advanced or metastatic TNBC with ≤ 3 prior lines of therapy were enrolled. Treatment includes a 2-week run-in with binimetinib followed by pembrolizumab. There were 2 dose levels (DL) with binimetinib at 45 mg at DL 0 and 30 mg at DL -1. A standard 3+3 design was used in Phase I, and Simon’s two-stage Optimal design was used in Phase II. PD-L1 22C3 was performed in archival samples with CPS ≥ 10 considered as positive (PD-L1+). Tumor-infiltrating lymphocytes (TILs) were quantified into 0, 1, 2, and 3+. Circulating tumor cells (CTC) and circulating cancer-associated macrophage-like cells (CAML) were isolated using CellSieve microfilters and immunofluorescently labeled with PD-L1 and p-ERK. Wilcoxon rank sum test, Chi-square test, Cox regression model, and Spearman correlation were used for analysis. Results: 22 patients were enrolled with a median age of 58 years old. Dose-limiting toxicity (DLT) was observed in 2 out of 4 patients in DL 0, with grade 3 ALT abnormality, flank pain, and nausea. In the next 6 patients in DL -1, there was 1 DLT with grade 3 AST/ALT abnormality. There were 17 patients treated with DL -1 and were evaluable for response. The objective response rate (ORR) was 29.41% (95% CI: 10.31-55.9) with 1 complete response (CR) and 4 partial responses (PR). The clinical benefit rate (CBR ≥ 24 weeks) was 35.29% (95% CI: 14.21-61.67). ORR in patients without liver metastases was 55.56% (95% CI: 21.20 - 86.30) and CBR was 66.67% (95% CI: 29.93-92.51). No response was observed in all 5 patients with liver metastases. There were 40.9% of patients with PD-L1 CPS ≥ 10. ORR in patients with PD-L1+ was 80%. However, 11.1% of patients with PD-L1 negative tumors also had an objective response and 44.4% of patients had clinical benefit ≥ 24 weeks. PD-L1 expression in archival tissue was associated with ORR (p 0.032) but not CBR (p 0.198), progression-free survival (PFS, p 0.373), and overall survival (p 0.348). TILs in archival tissue were also not associated with CBR (p 0.155) and PFS (p 0.157). One patient with TILs 0 had a stable disease ≥ 24 weeks and 2 patients TILs 1+ also had an objective response. We further evaluated blood-based biomarkers with CTC and CAML. Baseline PD-L1 in CAML (p 0.04) and decline in CAML size (p 0.02) after 1 cycle was significantly associated with CBR. However, baseline CTC count, CAML count (p 0.64), CAML size (p 0.46), p-ERK in CAML (p 0.23), and changes in CTC count, CAML count (p 0.83), p-ERK (p 0.07), and PD-L1 (p 0.08) in CAML were not significantly associated with responses. Using Cox regression analysis, a reduction in CAML count (p 0.02), CAML size (p 0.01), and PD-L1 in CAML (p 0.03) were associated with significant improvement in overall survival but not the reduction in p-ERK (p 0.6). However, PD-L1 expression in CAML is not associated with PD-L1 expression in archival tissue (Spearman correlation 0.13). Conclusions: Pembrolizumab and binimetinib at 30 mg are safe with manageable toxicities. Consistent with the preclinical data that MEKi can restore T cell function, promising activity was observed even in patients with low TILs and PD-L1 negative, particularly in patients without liver metastases. PD-L1 expression in peripheral blood CAML rather than archival tumor tissue may serve as a better biomarker to predict the clinical benefit of this combination. Early reductions in CAML count and size, were also significantly associated with responses. Future larger clinical trials are warranted to further evaluate the efficacy of this chemotherapy-free combination. Citation Format: Saranya Chumsri, Joseph Larson, Daniel Adams, Kathleen Tenner, Cha-Mei Tang, Morgan Weidner, Amanda Arnold, Dana Haley, Pooja Advani, Kostandinos Sideras, Alvaro Moreno-Aspitia, Edith Perez, Keith Knutson. Phase I/II study of pembrolizumab in combination with oral binimetinib in patients with unresectable locally advanced or metastatic triple-negative breast cancer [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 PO3-06-14.

Abstract Background: Activation of the RAS/MAPK pathway is associated with reduced tumor-infiltrating lymphocytes and poor outcomes in triple-negative breast cancer (TNBC). This trial evaluated the efficacy of pembrolizumab and MEK inhibitor, binimetinib. Here we evaluated potential biomarkers in peripheral blood to predict response. Methods: Patients with unresectable locally advanced or metastatic TNBC with ≤ 3 prior lines of therapy were enrolled. Treatment includes a 2-week run-in with binimetinib followed by pembrolizumab. There were 2 dose levels (DL) with binimetinib at 45 mg at DL 0 and 30 mg at DL -1. A standard 3+3 design was used in phase I, and Simon’s two-stage Optimal design was used in phase II. Circulating tumor cells (CTC) and circulating cancer-associated macrophage-like cells (CAML) were isolated using CellSieve microfilters and immunofluorescently labeled with PD-L1 and p-ERK. Wilcoxon rank sum test and Cox regression model were used for analysis. Results: A total of 22 patients were enrolled, with a median age of 58 years old. Dose-limiting toxicity (DLT) was observed in 2 out of 4 patients in DL 0, with grade 3 ALT abnormality, flank pain, and nausea. In the next 6 patients in DL -1, there was 1 DLT with grade 3 AST/ALT abnormality. There were 17 patients treated with DL -1 and were evaluable for response. The objective response rate (ORR) was 29.41% (95% CI: 10.31-55.9) with 1 complete response (CR) and 4 partial responses (PR). The clinical benefit rate (CBR ≥ 24 weeks) was 35.29% (95% CI: 14.21-61.67). ORR in patients without liver metastases was 55.56% (95% CI: 21.20 - 86.30), and CBR was 66.67% (95% CI: 29.93-92.51). There was no response observed in all 5 patients with liver metastases. Baseline mean CTC count was 1.3 cells, and CAML count was 8.9 cells/7.5 mL. Baseline PD-L1 in CAML (p 0.04) and decline in CAML size (p 0.02) after 1 cycle were significantly associated with CBR. However, baseline CTC count, CAML count (p 0.64), CAML size (p 0.46), p-ERK in CAML (p 0.23), and changes in CTC count, CAML count (p 0.83), p-ERK (p 0.07), and PD-L1 (p 0.08) in CAML were not significantly associated with responses. Using Cox regression analysis, a reduction in CAML count (p 0.02), CAML size (p 0.01), and PD-L1 in CAML (p 0.03) were associated with significant improvement in overall survival but not the reduction in p-ERK (p 0.6). Conclusions: Pembrolizumab and binimetinib at 30 mg are safe with manageable toxicities. Promising activity was observed in patients without liver metastases. Baseline PD-L1 expression, early reduction in CAML count, size, and PD-L1 expression were significantly associated with subsequent responses, providing potential noninvasive biomarkers to predict response to this combination. Future larger clinical trials are warranted to further evaluate the efficacy of this combination. Citation Format: Saranya Chumsri, Joseph J. Larson, Daniel L. Adams, Kathleen S. Tenner, Cha-Mei Tang, Morgan T. Weidner, Amanda N. Arnold, Dana L. Haley, Pooja Advani, Kostandinos Sideras, Alvaro Moreno-aspitia, Edith A. Perez, Keith L. Knutson. Peripheral blood biomarkers in Phase II study of pembrolizumab in combination with oral binimetinib in patients with unresectable locally advanced or metastatic triple-negative breast cancer. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 5454.

Abstract Background: Previous studies demonstrated that activation of the RAS/MAPK pathway is associated with reduced tumor-infiltrating lymphocytes and poor response to neoadjuvant chemotherapy in triple-negative breast cancer (TNBC). Further in vivo study showed that inhibition of the MAPK pathway with a MEK inhibitor is synergistic with immune checkpoint inhibitors (ICIs). Methods: Patients with unresectable locally advanced or metastatic TNBC with ≤ 3 prior lines of therapy were treated with pembrolizumab 200 mg every 3 weeks plus an oral MEK inhibitor binimetinib. Treatment was started with a 2-week run-in period with single-agent binimetinib. There were 2 dose levels in phase I, including dose level 0 (DL 0) with binimetinib at 45 mg orally twice daily continuously and dose level -1 (DL -1) at 30 mg twice daily. A standard 3+3 design was used in phase I to identify the recommended phase II dose (RP2D) and Simon’s two-stage Optimal design was used in phase II. Results: A total of 22 patients were enrolled. The median age was 58 years old (range 37-77). 14 (63.6%) patients had no prior systemic therapy in the metastatic setting and 8 (36.4%) patients had 1-2 prior lines of therapy. There were 4 patients treated in DL 0. Dose-limiting toxicity (DLT) was observed in 2 out of 4 patients in DL 0 with grade 3 ALT abnormality in one patient and grade 3 flank pain together with grade 3 nausea and vomiting > 48 hours despite anti-emetic therapy in the other patient. Binimetinib dose was reduced to DL -1. In the next 6 patients, there was 1 DLT observed with grade 3 AST/ALT abnormality. Thus, DL -1 was the RP2D, and an additional 12 patients were treated with DL -1 in phase II. Overall, 18 patients were treated in DL -1 and were included in phase II efficacy evaluation. 17 patients were evaluable for response. Objective responses were observed in 5 patients (29.41% 55.96) with 1 complete response (CR) and 4 partial responses (PR). The clinical benefit rate (CBR) was 35.29% (95% CI: 14.21 - 61.67) with 6 out of 17 having had CR, PR, or stable disease >= 24 weeks. Since previous studies showed poor responses to ICIs in patients with liver metastases due to macrophage-mediated T cell elimination, we further conduct exploratory analysis to evaluate responses among patients with and without liver metastases. Among all 5 patients with liver metastases, no response was observed. The objective response rate (ORR) in patients without liver metastases was 55.56% (95% CI: 21.20 - 86.30) and CBR was 66.67% (95% CI: 29.93-92.51), when excluding 3 patients who discontinued treatment due to adverse events prior to follow-up scans. Median progression-free survival in DL 0 was 2.4 (95%CI: 0.5-NE) and in DL -1 was 8.3 (95% CI: 3.9-NE) months. Median overall survival in DL 0 was 7 (95%CI: 0.5-NE) and in DL -1 was 33.2 (95% CI: 10.3-NE) months. Among patients who responded, 3 out of 5 (60%) had a duration of response greater than 12 months and ongoing even after stopping treatment (range: 5.4 - 32.0 months). Adverse events (AEs) were mostly grade 1-2 including anemia, CPK increase, fatigue, diarrhea, nausea, peripheral neuropathy, acneiform rash, AST increase, cardiac troponin increase, and constipation. Additional correlative studies are ongoing and will be presented at the meeting. Conclusions: Pembrolizumab in combination with binimetinib at 30 mg twice daily appears to be safe with manageable toxicities. Promising activity with durable responses was observed with this combination without chemotherapy, particularly in patients without liver metastases. Future studies are warranted to further evaluate the efficacy of this combination. Citation Format: Saranya Chumsri, Joseph J. Larson, Kathleen S. Tenner, Jun He, Mei-Yin Polley, Morgan T. weidner, Amanda N. Arnold, Dana Haley, Pooja Advani, Kostandinos Sideras, Alvaro Moreno-Aspitia, Edith A. Perez, Keith L. Knutson. Phase I/II study of pembrolizumab in combination with oral binimetinib in patients with unresectable locally advanced or metastatic triple-negative breast cancer [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P4-01-17.

Abstract Background Advances in the multidisciplinary care of hormone-receptor positive (HR+) early breast cancer (eBC) have markedly improved clinical outcomes: however, disease recurrence may still occur, particularly in patients (pts) with moderate or high-risk cancers at the time of diagnosis. The use of CDK4/6 inhibitors (CDK4/6i) combined with endocrine therapy (ET) is a standard of care for advanced breast cancer, supporting the rationale to study CDK4/6i in the eBC setting. Here we present the final protocol-planned analyses of the global phase III PALLAS trial investigating whether the addition of the CDK4/6i palbociclib (P) to adjuvant ET improves outcomes over ET alone for HR+/HER2- eBC. Methods PALLAS (PALbociclib CoLlaborative Adjuvant Study, NCT02513394) is a randomized phase III open-label trial in which pts with stage II-III HR+/HER2- eBC were randomized to receive either 2 years of P with adjuvant ET (P+ET) or ET alone. The primary endpoint is invasive disease-free survival (iDFS); secondary endpoints include distant recurrence-free survival (DRFS), locoregional recurrence-free survival (LRRFS), overall survival (OS), and safety. Mandatory biospecimen collection has supported the creation of an expansive translational science program, and long-term follow-up is planned. Revised sample size calculations required recruitment of 5600 pts in order to detect a 25% iDFS improvement in patients receiving P+ET with 85% power; this final protocol-planned analysis was planned after 469 iDFS events. Results From September 1, 2015 to November 30, 2018, 5,761 pts (median age 52 years, range 22-90) were randomized in 406 centers in 21 countries worldwide. 1,014 (17.6%) had stage IIA disease (capped) and 4,728 (82.1%) stages IIB/III. 4,754 (82.5%) had received prior (neo)adjuvant chemotherapy. After a protocol-planned 2nd interim analysis in May 2020 crossed the futility threshold, 349 P+ET pts still on active treatment stopped P and were transferred to follow-up. At the time of final analysis cutoff date (November 20, 2020), after a median follow-up of 31 months and 516 events recorded, iDFS was similar between the two arms, with 3-year iDFS of 89.3% (95% CI: 87.8-90.6%) for Palbo+ET, and 89.4% (88.0-90.7%) for ET alone (hazard ratio 0.96, 95% CI: 0.81-1.14). There was no statistically significant difference in secondary outcome endpoints. Subgroup analyses revealed no significant interactions between treatment effect and other factors (including risk category). The safety profile of P was as expected, with grade 3 or 4 neutropenia the most common side effect (safety population: 1759/2841 [61.9%] vs 11/2902 [0.4%]). Overall 42% of pts. discontinued P prior to the planned 2-year duration, 28.2% of Palbo+ET pts discontinued therapy due to adverse events, without an observed impact on survival outcomes. Conclusions Now with the full number of events, this analysis of the PALLAS trial shows that the addition of 2 years of P to ongoing adjuvant ET did not improve survival endpoints for pts with stage II-III HR+/HER2- eBC. Whether P is beneficial in the adjuvant setting for certain sub-groups of pts will be further evaluated with longer-term follow-up and by the ongoing translational science program. Support: ABCSG; AFT; Pfizer; ClinicalTrials.gov Identifier: NCT02513394; https://www.abcsg.org; https://acknowledgments.alliancefound.org Citation Format: Michael Gnant, Amylou C Dueck, Sophie Frantal, Miguel Martin, Hal Burstein, Richard Greil, Peter Fox, Antonio C Wolff, Arlene Chan, Eric Winer, Christian Singer, Kathy Miller, Marco Colleoni, Michelle Naughton, Gabor Rubovszky, Judith Bliss, Ingrid A Mayer, Guenther G Steger, Zbigniew Nowecki, Olwen Hahn, Norman Wolmark, Hope Rugo, Georg Pfeiler, Hannes Fohler, Otto Metzger, Céline Schurmans, Kathy P Theall, Dongrui R Lu, Kathleen Tenner, Christian Fesl, Angela DeMichele*, Erica L Mayer, *shared last authorship. Adjuvant palbociclib in HR+/HER2- early breast cancer: Final results from 5,760 patients in the randomized phase III PALLAS trial [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr GS1-07.

PURPOSE Palbociclib is a cyclin-dependent kinase 4 and 6 inhibitor approved for advanced breast cancer. In the adjuvant setting, the potential value of adding palbociclib to endocrine therapy for hormone receptor–positive breast cancer has not been confirmed. PATIENTS AND METHODS In the prospective, randomized, phase III PALLAS trial, patients with hormone receptor–positive, human epidermal growth factor receptor 2–negative early breast cancer were randomly assigned to receive 2 years of palbociclib (125 mg orally once daily, days 1-21 of a 28-day cycle) with adjuvant endocrine therapy or adjuvant endocrine therapy alone (for at least 5 years). The primary end point of the study was invasive disease-free survival (iDFS); secondary end points were invasive breast cancer–free survival, distant recurrence-free survival, locoregional cancer-free survival, and overall survival. RESULTS Among 5,796 patients enrolled at 406 centers in 21 countries worldwide over 3 years, 5,761 were included in the intention-to-treat population. At the final protocol-defined analysis, at a median follow-up of 31 months, iDFS events occurred in 253 of 2,884 (8.8%) patients who received palbociclib plus endocrine therapy and in 263 of 2,877 (9.1%) patients who received endocrine therapy alone, with similar results between the two treatment groups (iDFS at 4 years: 84.2% v 84.5%; hazard ratio, 0.96; CI, 0.81 to 1.14; P = .65). No significant differences were observed for secondary time-to-event end points, and subgroup analyses did not show any differences by subgroup. There were no new safety signals for palbociclib in this trial. CONCLUSION At this final analysis of the PALLAS trial, the addition of adjuvant palbociclib to standard endocrine therapy did not improve outcomes over endocrine therapy alone in patients with early hormone receptor–positive breast cancer.

Abstract Background: A previous neoadjuvant study in patients with triple negative breast cancer (TNBC) demonstrated that low tumor infiltrating lymphocytes (TILs) after neoadjuvant chemotherapy is associated with a poor outcome. Activation of RAS/MAPK pathway has been associated with reduced TILs. Preclinical studies showed that MEK inhibitor enhances immune responses and is synergistic with anti PD-1/PD-L1 therapy in TNBC. Methods: The standard Phase I 3+3 study design was used. Patients with unresectable locally advanced or metastatic TNBC with ≤ 3 prior lines of therapy were enrolled. Patients received single agent binimetinib for 2 weeks prior to an addition of pembrolizumab. Dose level 0 was binimetinib at 45 mg oral twice daily continuously and dose level -1 was 30 mg twice daily. Pembrolizumab was given at a fixed dose of 200 mg every 3 weeks in both dose levels. The maximum tolerated dose (MTD) was defined as the dose level below the lowest dose that induces dose-limiting toxicity (DLT) during the first 2 cycles in at least one-third of patients. Results: A total of 12 evaluable patients were enrolled in the phase I, 4 patients in dose level 0 and 8 patients in dose level -1. In dose level 0, among 3 out of 4 patients who were evaluable for DLT, 2 patients experienced DLTs, including grade (G) 3 nausea, vomiting, abdominal pain and G3 ALT elevation. Thus, the stopping rule was met and the dose level was adjusted to dose level -1. None of the first 3 patients in dose level -1 experienced a DLT. All three experienced other ≥ G3 AEs, including 1 G3 cardiac troponin T increased and 2 with G3 hypertension. 5 additional patients were accrued to dose level -1 and were evaluable for AEs. Three of these were evaluable for DLTs. One patient had G3 ALT/AST increase, deemed a DLT. However, this patient had liver metastasis and had G1 ALT/AST elevation at baseline. Her ALT/AST normalized in 3 weeks after treatment discontinuation and oral prednisone. Other ≥ G3 toxicities in the second group of 5 patients in dose level -1 include G3 hypertension (12.5%), nausea (12.5%), hypokalemia (12.5%), neutrophil count decrease (12.5%) dyspnea (12.5%), peripheral neuropathy (12.5%), and retinal detachment (12.5%). Since less than 1/3 of patients experienced DLT and there was no ≥ G4 AE at least possibly related to treatment over all cycles at any given dose level, the MTD was determined as dose level -1. Five patients are currently enrolled in the phase II section, and 10 more patients are needed. Objective response rate analysis will be performed once study enrollment is completed. Conclusions: The recommended phase II doses for pembrolizumab in combination with binimetinib are 200 mg every 3 weeks and 30 mg twice daily, respectively. The combination appears to be safe with manageable toxicities. Long term durable response has been observed. The phase 2 portion of this trial is currently on going. Citation Format: Saranya Chumsri, Jun He, David Hillman, Morgan Weidner, Morgan Weidner, Dana Haley, Aline Reis, Kathleen Tenner, Pooja Advani, Kostandinos Sideras, Alvaro Moreno-Aspitia, Edith Perez, Keith Knutson. Results of phase I study of pembrolizumab in combination with binimetinib in patients with unresectable locally advanced or metastatic triple negative breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr CT133.

548 Background: sTILs are a well-established prognostic and predictive biomarker in patients with operable TNBC receiving pre or postoperative systemic therapy. We1 and others2,3 have also shown that sTILs are prognostic in patients who did not receive adjuvant chemotherapy. Here, we detail the outcomes of systemically untreated patients with N0 TNBC according to sTIL score. We focused on the N0 subset as a group of patients who may be candidates for future prospective therapy de-escalation trials. Methods: From a clinically annotated cohort of 605 patients with centrally confirmed TNBC (ER/PR < 1% and HER2 negative) with long-term outcomes data, we identified 182 patients treated with locoregional therapy only (breast surgery +/- radiation therapy and no chemotherapy). The clinicopathological characteristics of this cohort have previously been published1. In this analysis, we report the 5- and 10-year invasive disease-free survival (iDFS) and overall survival (OS) rates of patients with N0 TNBC according to sTIL levels. IDFS and OS were defined as per the STEEP classification and estimated using the Kaplan–Meier method. Comparisons of the survival distributions between groups were assessed by the log-rank test. sTILs were assessed as a continuous parameter according to the International TIL Working Group guidelines. For comparisons of outcomes between groups, tumors were classified as lymphocyte-predominant TNBC (defined as containing ≥50% sTILs) vs non-lymphocyte-predominant ( < 50% sTILs). Results: Of 182 systemically untreated patients, 149 (82%) were N0 and most (78%) were post-menopausal. T stage distribution was T1: 68%, T2: 28%, T3/4: 4%. Among N0 patients, 31 (21%) had lymphocyte-predominant TNBC, and in this group the 5-year iDFS and OS were 89% (95% CI 76-100) and 96% (95% CI 89-100), while the 10-year iDFS and OS were 89% (95% CI 76-100) and 87% (95% CI 73-100), respectively. In contrast, outcomes for patients with non-lymphocyte predominant TNBC were significantly worse. For this group, 5-year iDFS and OS were 62% (95% CI 53-73) and 78% (95% CI 71-86) while the 10-year iDFS and OS were 45% (95% CI 36-58) and 66% (95% CI 68-76), respectively ( log-rank p = 0.02 for iDFS and log-rank p = 0.03 for OS). Conclusions: sTIL quantification identifies a subset of patients with early-stage N0 TNBC with an exceedingly good prognosis, even in the absence of adjuvant chemotherapy. These data provide support for the evaluation of sTILs as part of prospective investigation of systemic therapy de-escalation strategies in N0 TNBC. References:1Leon-Ferre et al, Breast Cancer Res Treat (2018) 167:89-99 2Park et al, Ann Oncol (2019) 12:1941-1949 3De Jong et al, ESMO 2020

BackgroundThe goal of this study was to assess the impact of trastuzumab on locoregional failure.METHODSThe analysis included 2763 patients with HER2‐positive (HER2+) breast cancer who were randomly assigned to adjuvant doxorubicin (A), cyclophosphamide (C), paclitaxel (T) and trastuzumab (H) (arm A, AC→T [n = 922]; arm B, AC→T→H [n = 988]; arm C, AC→T+H→H [n = 853]). Radiotherapy was given after AC→T concurrently with H. Radiotherapy was given after lumpectomy (L) or after mastectomy (M) with ≥4 positive lymph nodes but was optional for 1 to 3 positive lymph nodes. Locoregional failures at 10 years (LFR10) as first events were compared using competing risk analysis.ResultsThe median follow‐up was 13.0 years. The first site of failure was local‐only in 96 cases, locoregional in 16 cases, regional in 32 cases, and not specified in 2 cases; LFR10 was 4.8% (95% CI 4.1%‐5.7%). LFR10 was 5.5% (95% CI 4.3%‐7.2%), 4.9% (95% CI 3.7%‐6.4%), and 2.8% (95% CI 1.9%‐4.1%) in arms A, B, and C (B vs A: hazard ratio [HR] 0.91, P = .62; C vs A: HR 0.72, P = .12). For estrogen receptor–positive patients, LFR10 was 3.7% (95% CI 2.8%‐4.8%) and for estrogen receptor–negative patients, it was 6.1% (95% CI 5.0%‐7.4%; HR 0.61, P = .004). Local treatment included L+RT (n = 1044 [38%]), M+RT (n = 1025 [37%]), and M (n = 694 [25%]). LFR10 was 6.% (95% CI 5.0%‐7.8%), 3.0% (95% CI 2.1%‐4.3%), and 5.5% (95% CI 4.0%‐7.4%) for L+RT, M+RT, and M, respectively (M+RT vs L+RT: HR 0.43, P < .001; M vs L+RT: HR 0.88, P = .57). For 1 to 3 positive lymph nodes, LFR10 was 6.5% (95% CI 4.8%‐8.9%), 4.1% (95% CI 2.4%‐7.0%), and 4.3% (95% CI 2.9%‐6.5%) in L+RT, M+RT, and M, respectively (M vs L+RT: HR 0.68, P = .14; M vs M+RT: HR 1.2, P = .6).ConclusionLow 10‐year LFRs were seen regardless of trastuzumab use. Differences in local therapy in patients with 1 to 3 positive lymph nodes did not appear to improve local control. Local therapy studies for HER2+ and other tumor characteristics are important as the role of local therapies continues to evolve.

520 Background: Targeted therapy using trastuzumab (an anti-HER-2 receptor monoclonal antibody) has significantly improved survival in breast carcinoma patients (pts), but determining which pts will respond to this therapy remains a challenge. We previously reported (Miller DV, ASCO 2004 abstract #568) a subset of pts with breast cancers demonstrating focal HER-2 amplified clones (FHAC) amidst otherwise nonamplified tumor cells by fluorescence in-situ hybridization. These accounted for 21% of the HER-2 amplified but immunohistochemistry (IHC) negative cases and 30% of the HER-2 amplified but IHC equivocal cases. The clinical significance of this phenomenon was unclear at that time. We now report the disease-free survival (DFS) data on 91 FHAC pts with a comparison to the diffusely amplified (DA) cases in this trial group. Methods: Breast tumors were evaluated for HER-2 gene amplification using PathVysion™. FHAC cases demonstrated 2–40% of cells with >10 HER-2 signals and HER-2:CEP17 ratio >5.0, regardless of the overall HER-2:CEP17 ratio. Patient and disease characteristics were compared using chi-square tests. Cox regression models compared DFS between pts randomized to arms A (standard chemotherapy) and C (standard chemotherapy with concurrent trastuzumab) within 91 FHAC and 1571 DA cases. Median follow up was 4.0 years. Results: Age, race, menopausal status, surgical procedure, nodal status, histologic type and grade, and tumor size, were not significantly different between pateints with FHAC and DA. Pateints with FHAC had more frequent hormone receptor positivity compared to DA cases (66% vs 50%; p = 0.004). Hazard ratios between pts with FHAC and DA showed that both groups of pts had similar DFS (A: HR = 0.86, p = 0.65; C: HR = 0.72, p = 0.57). Hazard ratios between arms within FHAC and DA groups demonstrated similar benefit from trastuzumab in each group (FHAC: HR = 0.50, p = 0.30; DA: HR = 0.59, p < 0.0001). Results remained consistent when including hormone receptor status in the model. Conclusions: Based on a small number (n = 91) of pts with FHAC, benefit from trastuzumab appears to be similar whether the population of HER-2 amplified cells with breast carcinomas is focal or diffuse. [Table: see text]