Chumsri, Saranya

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.

Abstract Background: CCR5 is a motility chemokine receptor implicated in tumor progression, whose activation and endocytosis may identify highly aggressive breast cancer (BC) subtypes likely to spread via the circulatory system. We first studied the activation and endocytosis of CCR5 in response to its ligand CCL5 (RANTES) in the model BC cell line MDA-MB231. We then screened two types of circulating tumor-associated cells (TACs) with known negative clinical outcomes, 1) circulating tumor cells (CTCs) and 2) cancer-associated macrophage-like (CAMLs) cells, to evaluate CCR5 upregulation in relation to disease progression in metastatic breast cancer (mBC). Methods: MB231 cells were used to visualize CCR5 activation within the cell's surface and intracellular space using an anti-CCR5 antibody after stimulation with RANTES. MB231 cells were stained with LAMP-1A to verify co-localization of CCR5 and RANTES to endosomes. Anonymized peripheral blood samples from (n=54) mBC patients were obtained in accordance with local IRB regulations and with informed consent. TACs were isolated using a low-flow CellSieve Microfiltration system and stained for Cytokeratin, CD45, and CCR5. CCR5 expression signal and localization were evaluated on all TACs via fluorescence microscopy. Results: CCR5 in MB231 cells appeared as ~1μm clusters known as “CCR5 pools”, which can be found on the cell's surface, within the cytoplasm, and in the nuclear space. CCR5 pools were upregulated in the presence of RANTES, which appears to relate to endocytosis and nuclear translocation. Within the TACs of mBCs, we found similar patterns of CCR5 pooling with 70% of patients (n=38) having CCR5+ CAMLs and 41% (n=22) having CCR5+ CTCs. It was found that higher numbers of CCR5 pools (≥10pools/cell) were correlated to a 2-fold increase in both CTCs and CAMLs in circulation. In the analysis of outcome data, it was determined that patients having ≥10 CCR5 pools on their CAMLs was a highly significant predictor of worse progression free survival (PFS) and overall survival (OS) (PFS HR=4.8, CI 95% 1.9-11.6, p=0.0015) and (OS HR=3.6, CI 95% 1.3-10.0, p=0.0331). In CTCs ≥10 pools/cell was not a significant predictor for worse PFS and OS. However, ≥5 CCR5 pools/cell significantly predicted for worse PFS but not OS (PFS HR=2.9, CI 95% 1.2-7.4, p=0.0418 and OS HR=3.3, CI 95% 1.1-9.3, p= 0.0539). Conclusion: We observed the activation and endocytosis of CCR5 pools using RANTES in MD-MB231 cell lines, and then demonstrated that this upregulated motility pathway appears to be conserved in migratory cells in mBC patients. Further, this upregulation of CCR5 appears to correlate with worse clinical outcomes, which may provide an explanation for how tumor-associated cells move into circulation and acquire metastatic potential. Citation Format: Ashvathi Raghavakaimal, Massimo Cristofanilli, Cha-Mei Tang, R. K. Alpaugh, Kirby P. Gardener, Saranya Chumsri, Daniel L. Adams. CCR5 upregulation in two subtypes of tumor associated circulating cells predict worse prognosis in metastatic 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 589.

3039 Background: Patients with multiple organ metastases have poorer prognoses than those with a single organ metastasis, are frequently associated with drug resistance, and have higher tumor burden. Engorged (≥50um) Cancer Associated Macrophage-Like Cells (CAMLs) are a circulating stromal cell subtype detected in the blood of patients with solid tumors at high risk for recurrence or progression. While numerous studies have shown that ≥50um CAMLs predict poor clinical outcomes, meta-analysis of these studies have also suggested that hyper engorged CAMLs ≥100um (heCAMLs) may be associated with multifocal metastatic disease and even worse outcomes. In this prospective study, we evaluated the presence of heCAMLs in patients with metastatic disease and demonstrated a strong relationship with multi organ spread, which also correlated with shorter Progression Free Survival (PFS) and Overall Survival (OS). Methods: We prospectively recruited 151 patients with metastatic (m) mbreast (n = 58), mlung (n = 34), mprostate (n = 39), and mrenal (n = 20) cancers. Peripheral blood was collected prior to the induction of new treatment for metastatic cancer. Cells were isolated following standard CellSieve techniques, then imaged and measured in ZenBlue. Multi organ metastasis was defined as spread to ≥2 distant organ sites, or any spread to the brain. Single factor ANOVA was conducted to compare heCAML presence in multi organ metastatic patients versus patients with single organ site metastasis. Univariate and multivariate analysis was run to evaluate for PFS and OS against heCAMLs, and all known clinical parameters. Results: 150 viable samples (excluding 1 failed sample) were obtained. Multi organ metastases were present in 55% (n = 83/150) of patients. heCAMLs were found in 59% (n = 49/83) of the multi organ metastatic population, but only in 16% (n = 11/67) of the single site metastatic cohort (p < 0.001). heCAML presence appeared to differentiate multi organ vs single organ metastases in mbreast (85% vs. 52%, p = 0.006), mlung (71% vs. 26%, p = 0.025), mprostate (75% vs. 37%, p = 0.029), and mRCC (88% vs. 36%, p = 0.025). Further, in all n = 150 patients, heCAML presence predicted a significantly shorter median PFS of 4.5 versus 7.2 months, 24 month PFS (HR = 1.67, 95%CI = 1.13-2.45, p = 0.013), and significantly shorter median OS of 13.1 versus 20.4 months, 24 month OS (HR = 2.05, 95%CI = 1.24-3.39, p = 0.008). Conclusions: We examined a non-invasive prognostic blood based assay to determine its relationship to multi organ metastatic spread as well as its prognostic value in several solid cancers. These results showed patients with heCAMLs had higher rates of multi organ metastases, and appear to predict for shorter PFS and OS. Studies of larger cohorts are needed for prospective validation of these initial findings.

535 Background: Invasive lobular carcinoma (ILC) is a rarer form of breast cancer, accounting for 10% of the disease cases. HER2 overexpression in ILC is infrequent and limited data exist regarding clinical characteristics and outcome of HER2-positive (HER2+) ILC patients (pts) treated with adjuvant trastuzumab. Methods: Patient characteristics were compared between ILC and invasive ductal carcinoma (IDC) using Wilcoxon rank sum test for continuous variables and Chi-square test for categorical variables. Kaplan-Meier (KM) method was used to estimate the freedom from mortality and recurrence. Cox regression model was used to evaluate the association between ILC and outcomes adjusted for other characteristics. NanoString technology was used to quantify mRNA to develop immune-related gene signatures. Results: From a total of 3,304 pts, 122 (3.7%) pts had ILC. Pts with ILC were significantly older (median age 54 vs. 49 years), had larger tumors, lower grade, more ER and PR positive tumors, and more lymph node involvement (25.4% had N3 disease compared to 12.7% in IDC). Overall, with KM analysis, pts with ILC had significantly worse overall survival (OS, p = 0.005) and recurrence-free survival (RFS, p = 0.046) compared to IDC. The 15-year freedom from recurrence was merely 57.67% in ILC compared to 72.68% in IDC. A significant number of hormone receptor-positive (HR+) ILC pts developed late recurrence with cumulative event rates increasing from 23% at 5 years to 42% at 15 years. Nevertheless, in multivariate Cox regression analysis adjusting for other clinical characteristics, including age, tumor size, grade, ER/PR, and lymph node status, lobular histology was not significantly associated with worse outcome for OS (HR = 1.19, 95%CI 0.67-2.1, p = 0.55) and RFS (HR = 1.5, 95%CI 0.9-2.5, p = 0.12), as compared with IDC. However, ILC pts appeared to have similar degree of benefit from trastuzumab, with RFS HR = 0.58 compared to HR = 0.67 in the entire population. For immune landscape, there was no significant difference in gene signatures related to CD45, CD8, B cells, or cytotoxic cells. However, ILC had more enrichment in mast cell gene signature and fewer macrophage, NK CD56dim, and regulatory T cell signatures compared to IDC (p < 0.05). Conclusions: HER2+ ILC has distinct clinical characteristics and immune landscape compared to IDC. ILC pts appeared to have worse outcome compared to IDC likely because ILC pts often presented with more locally advanced disease. However, similar benefit of trastuzumab was observed in ILC pts. Due to high risk of late relapse in HR+ HER2+ ILC, extended adjuvant endocrine therapy should be considered in this group of high-risk pts. Clinical trial information: NCT00005970.

524 Background: PREDICT+ is a widely used, free, online tool based on traditional clinico-pathological features, including HER2, developed to predict individual mortality of EBC pts and to aid clinical decision making for adjuvant therapy. However, its prognostic role in HER2+ EBC pts treated with chemotherapy (CT) and anti-HER2 therapies remains unclear. We aimed to investigate the prognostic performance of PREDICT+ in HER2+ EBC pts enrolled in the ALTTO trial. Methods: ALTTO is a phase III study evaluating adjuvant lapatinib (L) +/- trastuzumab (T) vs. T alone in pts with HER2+ EBC. Pts enrolled in the ALTTO trial and receiving T-based therapy started concurrently with CT were eligible for this analysis. We calculated PREDICT+ estimates using variables extracted from ALTTO database, blinded to pts outcomes. The prognostic performance of PREDICT+ was evaluated by assessing its calibration and discriminatory accuracy. For calibration, median predicted 5-year (5-yr) overall survival (OS) was compared to observed 5-yr OS. For discriminatory accuracy, the area under the receiver-operator characteristic (AUC under the ROC) curve and corresponding 95% confidence intervals (CI) for predicted 5-yr OS were calculated. Subgroup analyses were performed according to type of anti-HER2 therapy, type of CT, age, hormone receptor (HR) status, nodal status and tumor size. Results: This analysis included 2,794 pts. After a median follow-up of 6.0 years (IQR, 5.8-6.7), 182 deaths were observed. Overall, PREDICT+ underestimated 5-yr OS by 6.7% (95% CI, 5.8-7.6): observed 5-year OS was 94.7% vs. predicted 88.0%. The underestimation was consistent across all subgroups (Table). For discriminatory accuracy, AUC under the ROC curve was 73.7% (95%CI 69.7-77.8) in the overall population, ranging between 61.7% and 77.7% across the analysed subgroups. Conclusions: In HER2+ EBC pts enrolled in the ALTTO trial, the PREDICT+ score highly underestimated OS. The low performance of this prognostic tool was consistent across all pts subgroups. PREDICT+ should be used with caution to give prognostic estimation in HER2+ EBC pts treated in the modern era with effective chemotherapy and anti-HER2 targeted therapies.[Table: see text]

Abstract Background: Growing data established the pivotal role of preexisting immune response in triple negative breast cancer (TNBC). Conventionally, preexisting immune response can be evaluated by quantifying tumor infiltrating lymphocytes mainly in the stroma or gene expression analysis from the whole tumor section. Due to technical challenges with these conventional methods, limited data regarding specific subtypes and spatial distribution of these immune infiltrates are currently available. Methods: NanoString IO360 gene expression analysis and Digital Spatial Profiling (DSP) were used. DSP was used to quantify 29 immune-related proteins in stromal and tumor-enriched segments from 44 TNBC samples from the FinXX trial (NCT00114816) and 335 samples from the Mayo Clinic (MC) cohort of centrally reviewed TNBC (Leon-Ferre BCRT 2018). In FinXX trial, 22 patients with recurrence and 22 patients without recurrence were included. In MC cohort, 217/335 patients received adjuvant chemotherapy while 118 patients had surgery only without adjuvant chemotherapy. Regions were segmented based on pancytokeratin staining. The general linear model was used for statistical analysis of differential expression with recurrence free survival (RFS) as a categorical variable (recur yes or no). Kaplan-Meier (KM) estimates and Cox regression models were also used for analysis. Results: In the FinXX trial, there were 12 out of 29 proteins in tumor epithelial segments (intraepithelial) which were significantly expressed at higher levels among patients who were free of recurrence. These proteins include Beta-2 microglobulin, CD11c, CD20, CD40, CD56, CD8, Granzyme B, HLA-DR, ICOS, PD-L1, PD-L2, and TGFB1. In contrast, merely 5 out of 29 proteins in stromal segments were significantly differentially expressed in these 2 groups of patients. Granzyme B, IDO1, PD-L1, and PD-L2 in stroma were significantly higher and SMA was significantly lower in patients without recurrence. Using Cox regression models, intraepithelial CD56, CD40, and HLA-DR were significantly associated with outcome. When comparing between highest and lowest intraepithelial protein expression by tertile, intraepithelial CD56 (HR 0.12, 95%CI 0.03-0.39, p &lt; 0.001), CD40 (HR 0.13, 95%CI 0.04-0.46, p = 0.002), and HLA-DR (HR 0.24, 95%CI 0.06-0.89, p = 0.032) were significantly associated with improved outcome. However, expression of these same proteins in stroma was not associated with outcome. Using KM estimates, intraepithelial CD56 (p &lt; 0.0001), CD40 (p = 0.0006), and HLA-DR (p = 0.013) were also significantly associated with improved outcome. Nonetheless, RNA expression of these proteins by IO360 from whole tumor sections were not significantly associated with outcome (CD56 p = 0.27, CD40 p = 0.21, HLA-DR p = 0.48). Similar findings with DSP were observed in MC TNBC cohort. Comparing between the highest and lowest quartiles, there were significantly fewer patients who developed recurrence with high protein expression of intraepithelial CD56 (p &lt; 0.001), CD40 (p = 0.002), and HLA-DR (p = 0.006). Conclusions: Using an in-depth analysis with spatially defined context, we identify that there were numerically more intraepithelial immune-related proteins associated with outcome compared to proteins in stroma. Specifically, intraepithelial CD56, CD40, and HLA-DR were significantly associated with improved outcome in both FinXX and MC TNBC cohorts. However, neither expression of these proteins in stroma nor RNA expression from whole tumor were associated with outcome. Our study highlights the impact of spatial biology and the importance of evaluating each potential biomarker in a spatially defined manner. Support: W81XWH-15-1-0292, BCRF 19-161, P50CA116201-9, P50CA015083 Citation Format: Saranya Chumsri, Jodi M. Carter, Yaohua Ma, Douglas Hinerfeld, Heather Ann Brauer, Sarah Warren, Torsten O. Nielsen, Karama Asleh, Heikki Joensuu, Edith A. Perez, Roberto A. Leon-Ferre, David W. Hillman, Judy C. Boughey, Minetta C. Liu, James N. Ingle, Krishna R. Kalari, Fergus J. Couch, Keith L. Knutson, Matthew P. Goetz, E. A. Thompson. Spatially defined immune-related proteins and outcome in triple negative breast cancer in the FinXX trial and Mayo Clinic cohort [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PS6-02.

Abstract Background: Although risk of late relapse in hormone receptor-positive (HR+) breast cancer is well established, most existing data pertain to the HR+ HER2-negative (HER2-) subgroup. CTS5 is one of the models for predicting risk of late relapse in HR+ HER2- breast cancer. However, the value of this model in HR+ HER2+ disease is less known, particularly in the context of adjuvant trastuzumab. Here, we evaluated CTS5 in patients with early stage HR+ HER2+ breast cancer treated in the NCCTG N9831 (Alliance for Clinical Trials in Oncology) and NSABP B-31 (NRG) trials. Methods: Stage I-III HR+ (ER+ and/or PR+) HER2+ breast cancer patients who were free of recurrence after 5 years in N9831 and B-31 trials were included. The online CTS5 calculator was used to determine CTS5 score and risk group (low, intermediate, and high) based on age, tumor size, grade, and number of involved nodes. Kaplan-Meier (KM) estimates, Cox regression models, and C index were used for analysis. N9831 and B-31 trials were analyzed separately. Results: 1,204 patients in N9831 and 658 patients in B-31 met the entry criteria. Baseline characteristics were similar between both trials, including median age, tumor size, and follow up. Similar distribution within CTS5 risk group was observed in both trials; 68.2% and 70.1% patients were high risk, 24% and 21.9% as intermediate risk, as well as 7.8% and 8.1% as low risk classified in N9831 and B-31, respectively. Using univariate Cox regression analysis, CTS5 score as a continuous variable was associated with recurrence-free survival (RFS) in the entire study cohort, including patients who received chemotherapy alone or in combination with trastuzumab, (HR 1.37, 95%CI 1.03-1.81, p=0.03, C index 0.57 in N9831 and HR 1.36, 95%CI 1.06-1.76, p=0.02, C index 0.54 in B-31), but not in patients who received concurrent trastuzumab (HR 1.19, 95%CI 0.73-1.2, p=0.49, C index 0.54 in N9831 and HR 1.35, 95%CI 0.96-1.9, p=0.08, C index 0.54 in B-31). As categorical variable in the entire study cohort, CTS5 risk group was not significantly associated with RFS among patients with intermediate vs. low (HR 0.47, 95%CI 0.18-1.22, p=0.12 and HR 1.61, 95%CI 0.66-3.92, p=0.29) and high vs. low (HR 1.23, 95%CI 0.57-2.67, p=0.6 and HR 1.93, 95%CI 0.85-4.41, p=0.12) with the C index of 0.58 and 0.53 in N9831 and B-31 respectively. There was also no significant difference in RFS among 3 CTS5 risk groups with Kaplan-Meier estimates. Among patients who received concurrent trastuzumab, similar trends were observed with no statistical difference in RFS between high vs. low (HR 0.68, 95%CI 0.24-1.97, p=0.48 and HR 1.44, 95%CI 0.52-3.96, 0.49) with the C index of 0.55 and 0.51 in N9831 and B-31, respectively. Paradoxically, patients with intermediate risk had better RFS than low risk (HR 0.18, 95%CI 0.03-0.97, p=0.05) in N9831 but no significant difference in B-31 (HR 1.31, 95%CI 0.44-3.95, p=0.63). Conclusions: While CTS5 score as a continuous variable was associated with outcome in overall HR+ HER2+ population, this model was not prognostic in patients receiving adjuvant trastuzumab in both N9831 and B-31 trials. Furthermore, the correlation (C index) was modest and CTS5 risk group as a categorical variable could not stratify outcome in this group of patients. This study underlines the need to develop a new prognostic model to better delineate the risk of late relapse in HR+ HER2+ breast cancer patients receiving trastuzumab as this model can facilitate clinical decision for extended adjuvant endocrine therapy. Support: BCRF-19-161, U10CA180821, U10CA180868 and U10CA180822 (NRG), Genentech. https://acknowledgments.alliancefound.org Citation Format: Tanyami Pai, Angelica Gil, Yaohua Ma, Zhuo Li, Pooja Advani, Moreno Moreno-Aspitia, Gerardo Colon-Otero, Edith A. Perez, Yan Asmann, Katherine Pogue-Geile, E. A. Thompson, Saranya Chumsri. Prognostic value of clinical treatment score post-5 years (CTS5) and late relapse risk in hormone receptor-positive HER2-positive breast cancer in the North Central Cancer Treatment Group (NCCTG) N9831 (Alliance) and NSABP B-31 (NRG) trials [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PS6-03.

Abstract Background: Cyclin dependent 4/6 kinase inhibitors (CDK4/6i) and endocrine therapy (ET) have improved progression-free survival (PFS) and overall survival in hormone-receptor (HR)-positive metastatic breast cancer (MBC), but progression of disease is inevitable. Serum thymidine kinase-1 (TK1) is a secreted marker of proliferation that is prognostic in patients (pts) with HR-positive, HER2-negative MBC and may be predictive of ET and CDK 4/6i response. PROMISE (NCT0281902) is a prospective study enrolling women with HR-positive MBC starting palbociclib (Pb) + letrozole (L) (1st line) or Pb + fulvestrant (2nd line). We undertook a comprehensive “omic” assessment of blood, tumor, urine and the fecal microbiome in order to identify novel genomic variants and pathways associated with an early decline in TK1 (measured after 2 months) and PFS. Additionally, patient derived xenografts/organoids were generated at baseline and progression to test new therapeutic approaches to overcome resistance to CDK4/6i and ET. We report the initial association between the baseline genomic landscape and baseline TK1 levels. Methods: FFPE tumor biopsies were obtained for DNA/RNA sequencing (TempusTM) and blood samples for TK1 (Divitum® assay, Biovica) were collected pretreatment (pre-Pb) and after 2 cycles of Pb + ET (post-Pb2). Both whole-exome (exome capture) sequencing (WES) and RNA-Seq used the Integrated DNA Technologies xGen Exome Research Panel v1.0 capture kit. TK1+ disease was defined as &gt; 200 Du/L and TK1- disease as below limit of detection up to 200 Du/L. We tested the association between genomic and transcriptomic characteristics with baseline TK1 data in pretreatment samples where both WES and RNA-seq and TK1 was available. The data were analyzed using bioinformatics pipelines for somatic and germline mutations and copy number alterations. The current analysis focuses on baseline 1st-line pre-Pb omics data in conjunction with baseline TK1 levels. The database was locked for analysis on 5/29/2020. Results: Thirty-three pts (median age: 59 yrs.) were evaluable, with paired samples for TK1 in 32. Six pts had TK1+ disease pre-Pb and post-Pb2. Twenty-two pts had TK1- disease pre-Pb and post-Pb2. Four pts had a decrease in TK1 after 2 cycles of treatment that altered the classification from TK1+ to TK1-. Both baseline RNA seq and serum TK1 (n=16) were available for 4 TK1+ and 12 TK1- pts. In this group, 476 genes were differentially regulated (398 upregulated; 78 downregulated). Pathway analysis demonstrated enrichment in complement and coagulation cascade pathway, PPAR signaling pathway, and metabolism-related pathways related to up-regulation of CYP and UGT gene families. Further testing for the association of WES data with baseline TK1+ (n=8) and TK1- (n=16) disease demonstrated somatic copy number variations on chromosomes 6, 11, 12 and 15. CDK4 copy number gains were observed in 3/8 TK1+ pts and 0/16 TK1- pts. We also observed that somatic mutations (LOH, copy number and/or SNV/INDELs) were more prevalent in the TK1+ compared to the TK1- pre-Pb group in several cancer-associated genes (FAS [p=0.06] PTEN, PIK3CB, NAB2, SOX9 and FAT1 [p=0.08], TP53, and MAP2K4 [p=0.22]). Conversely, we also noted that 6/7 pts with GATA3 mutations had TK1- disease (p=0.23). Conclusions: Using a comprehensive “omics” approach, our data suggest that a secreted biomarker of proliferation (TK1) obtained prior to initiating CDK4/6i and ET for the first line treatment of HR+ MBC is associated with established and novel genes and pathways associated with prognosis of pts receiving ET and CDK 4/6i. Analysis of on-treatment (after 2 cycles) tumor RNA seq and its association with change in TK1 as well as data from the 2nd-line cohort will be presented at the meeting. Citation Format: Ciara C O Sullivan, Krishna R Kalari, Vera J Suman, Peter T Vedell, Ann Moyer, Abraham D Eyman Casey, Jason Sinnwell, Xiaojia Tang, Kevin Thompson, Alvaro Moreno-Aspitia, Donald W Northfelt, Minetta C Liu, Tufia C Haddad, Saranya Chumsri, Prema Peethambaram, Kathryn J Ruddy, Karthik V Giridhar, Roberto A Leon-Ferre, Adrian Nordmark, Mattias Bergqvist, Brendan P McMenomy, Richard M Weinshilboum, Liewei Wang, Matthew P Goetz. Novel genomic variants and pathways associated with baseline serum thymidine kinase 1 levels in HR-positive HER2-negative MBC patients commencing palbociclib and letrozole [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PS5-24.

Abstract Introduction: Stromal tumor-infiltrating lymphocytes (sTILs) have established prognostic and predictive significance in triple-negative breast cancer (TNBC). However, the roles of other immune cells in TNBC are less well-established. We performed high-plex quantitative spatial profiling in a cohort of early-stage TNBC to 1) apply spatial context to tumoral immune landscapes and 2) identify immune proteins associated with clinical outcomes, independently of TILs and other established prognostic clinicopathologic variables, in patients (pts) treated with or without adjuvant chemotherapy (CTX). Methods: The Mayo TNBC cohort comprises pts with centrally-verified, CTX-naive tumors resected from 1985-2012. Using a cohort-based TMA, with Nanostring GeoMX DSP, we quantitated 58 proteins within spatially-distinct intra-epithelial, cytokeratin-positive tumor segments and adjacent cytokeratin-negative/nuclei-positive stromal segments. Differentially-expressed (DE) proteins were identified using a negative binomial generalized linear model (SNR&gt;2, p&lt; 0.05) and a target DE protein set was dichotomized (80th percentile). After adjusting for prognostic clinicopathologic variables, proteins associated with recurrence-free survival (RFS, defined as time from surgery to either local, regional, and distant recurrence, or death by any cause) were identified by performing variable selection using the Akaike Information Criterion (AIC) obtained from fitting all possible Cox proportional hazards regression models (performed separately for intra-epithelial/stromal segments, and in groups +/- adjuvant CTX. Results: From the TNBC TMA, DSP data (N=250 tumors) included 169 pts who received adjuvant CTX+ and 81 who did not (CTX-). Overall, 85/250 developed recurrent disease. In the CTX+ group, intra-epithelial tumor segments from pts without recurrent disease were enriched in 10 immune proteins, including CD8, markers involved in antigen presentation/dendritic cells (CD11c, CD40, HLA-DR) or NK cells (CD56) (FC: 1.4-2.1, p&lt;0.05); CD14 was increased in stroma (FC: 1.5, p&lt;0.05). In contrast, in the CTX- group, both the intra-epithelial tumor and stromal segments from pts without recurrences were enriched in immune proteins (N= 12 and 15 respectively; FC 1.6-5.5, p&lt; 0.05) most markedly CD40, IDO1 and HLA-DR (FC: 3.2-5.5, p&lt; 0.05). Overall, CD3, CD4, CD27, CD44, and ICOS among others were enriched only in the CTX- group; CD14 and CD56 were enriched only in the CTX+ group. Based on these spatial data, biologic function and DSP data from another set of TNBC (FinXX trial), CD11c, CD14, CD27, CD40, CD56, and IDO1 were selected for RFS analysis. After applying our model selection criterion and adjusting for pt age at surgery, tumor size, lymph node status, and sTILs, intra-epithelial CD56 was independently associated with improved RFS in the CTX+ group (HR: 0.31[0.12, 0.81]). In the CTX- group, intra-epithelial CD11c was independently associated with improved RFS (0.10 [0.01, 0.81]). Conclusion: In this early-stage TNBC cohort, spatially-distinct tumor immune landscapes were associated with RFS but differed according to receipt of CTX after surgical resection. In the patients who received CTX, the intra-epithelial compartment, rather than stromal compartment, was immune-enriched in pts without recurrences. Among a targeted protein set, intra-epithelial CD56 remained associated with improved outcomes, independent of sTILs and other clinicopathologic features. In the CTX- group, spatial landscapes were more balanced, and intra-epithelial CD11c was independently associated with improved outcomes. These data provide insight into the spatial context of intrinsic immune landscapes in TNBC, and identify candidate prognostic immune biomarkers which may inform therapeutic strategies. Citation Format: Jodi M Carter, Saranya Chumsri, David W Hillman, David M Zahrieh, Yaohua Ma, Xue Wang, Jennifer M Kachergus, Judy C Boughey, Minetta C Liu, Krishna R Kalari, JC Villasboas, Roberto A Leon Ferre, Fergus J Couch, Matthew P Goetz, E. Aubrey Thompson. Intra-epithelial tumor immune landscapes are associated with clinical outcomes in early-stage triple-negative breast cancer [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PS16-01.

Abstract Background: In HER2-positive breast cancer patients, timing from the end of (neo)adjuvant trastuzumab (T)-based therapy to diagnosis of metastatic breast cancer is the key factor in determining the optimal first-line treatment. There is currently lack of clear evidence to support the possible prognostic role of this interval and 12 months has been mostly empirically used. The present analysis aimed to investigate patterns of relapse, first-line choice and survival outcomes of patients with HER2-positive early breast cancer who relapsed after adjuvant T-based therapy depending on T-free interval (TFI, i.e. timing from end of adjuvant T to diagnosis of distant metastases). Methods: In ALTTO, HER2-positive early breast cancer patients were randomized to 1 year of either T alone, lapatinib (L) alone, their sequence (T–&gt;L) or their combination (T+L). This exploratory analysis included only pts in the T or T+L arms who experienced a distant disease-free survival (DDFS) event. Two cohorts of patients were defined depending on TFI: group A (TFI of &lt;12 months) and group B (&gt;12 months). Baseline characteristics, patterns of relapse, first-line choice and overall survival (OS) were compared. OS was defined as time between date of DDFS event to death; age at diagnosis, tumor size and hormone receptor status were the variables included in the final multivariate models. Results: Out of 8,381 patients included in ALTTO, 404 patients in the T and T+L arms developed a DDFS event, of whom 201 occurred &lt;12 months (group A) and 203 &gt;12 months (group B) after the end of adjuvant T. Patients in group A were older (p=0.013), had larger tumors (p=0.004) and more frequently hormone receptor-negative disease (p&lt;0.001). No significant difference in patterns of first DDFS event was observed (p=0.073); however, a numerically higher number of patients in group A compared to group B developed brain metastasis (26% vs. 15%). First-line anti-HER2 therapy was received by 57% of the patients. Choice of first-line anti-HER2 therapy was different between the two groups (p=0.022): the majority of patients received T in both groups (61% vs. 65% in groups A and B, respectively), while more patients in group A received L (25% vs. 11%) and less received pertuzumab (8% vs. 17%). OS survival was significantly shorter in group A compared to group B: median OS was 18.4 and 29.3 months in groups A and B, respectively (adjusted HR 0.69; 95% CI 0.54-0.89; p=0.004). Similar results were observed after the exclusion of patients treated with first-line pertuzumab-based therapy (n=29): median OS was 18.2 and 26.8 months in groups A and B, respectively (adjusted HR 0.66; 95% CI 0.51-0.86; p=0.002). Better outcomes in terms of OS for patients in group B was observed across all analyzed subgroups with no interaction according to hormone receptor status (p=0.814) nor type of adjuvant anti-HER2 treatment (p=0.233): hormone receptor-positive (adjusted HR 0.69; 95% CI 0.48-0.99), hormone receptor-negative (adjusted HR 0.68; 95% CI 0.48-0.98), T+L arm (adjusted HR 0.55; 95% CI 0.38-0.80) and T arm (adjusted HR 0.80; 95% CI 0.55-1.17). Conclusions: In the ALTTO trial, HER2-positive early breast cancer patients who experienced shorter TFI (i.e. &lt;12 months vs. &gt;12 months) following adjuvant T-based therapy had inferior OS after the diagnosis of distant recurrence. Given its prognostic value, TFI can help to individualize clinical recommendations and to design future trials in the metastatic setting for patients relapsing after prior exposure to anti-HER2 therapy for early disease. Citation Format: Matteo Lambertini, Dominique Agbor-Tarh, Otto Metzger-Filho, Noam Ponde, Francesca Poggio, Florentine Hilbers, Larissa A Korde, Saranya Chumsri, Olena Werner, Lucia Del Mastro, Rafael Caparica, Volker Moebus, Alvaro Moreno-Aspitia, Martine Piccart, Evandro de Azambuja. Prognostic role of distant disease-free interval from completion of adjuvant trastuzumab in HER2-positive early breast cancer: Analysis from the ALTTO (BIG 2-06) trial [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PD3-04.