Abstract P5-03-04: Targeting the tumor microenvironment by CXCR4 inhibition to abrogate trastuzumab resistance in HER2-positive breast cancer

Background: Despite the fact that trastuzumab alongwithotherHER2-targetingdrugshavesignificantlyimprovedthe survival of patients with HER2 overexpression breast cancers (HER2+BC), resistance to trastuzumab is a clinical challenge in HER2+BC. Discerning actionable mechanisms of resistance to trastuzumab remains an important unmet need. WepreviouslyreporteddysregulationofCXCR4involvedintrastuzumab-resistance,butitscausal roleandthe associated mechanismsremainunknown.

Methods We established trastuzumab-resistant (TR) human breast cancer HER2+ cell lines by continuously exposing cells to trastuzumab (20 μg/ml) for at least 6 months. CXCR4 expressionwasassessed in TR cells or parental cells with Westernblot.QuantitativedensitometricanalysisofthedensitywasperformedwithAlphaViewSAsoftware.Relevant cell phenotypes were measured, including mammosphere formation, in vitro antibody-dependent cellular cytotoxicity (ADCC) assay, and cell invasion induced by 10% fetal bovine serum with or without 100ng/ml stromal cell-derived factor-1α (SDF-1α, CXCL12), the ligand of CXCR4. ANOVAwasusedtotest differencesbetweenmorethantwogroups,whilethedifferencesbetweentwogroupswereassessedbasedon pairedt-test.

Results: To better capture the heterogeneity of HER2+BC, we chose two trastuzumab-sensitive cell lines, BT474 (HER2+/HR+) and SKBR3 (HER2+/HR-) and an intrinsically trastuzumab-resistant cell line, HCC1419 (HER2+/HR-). We found much higher CXCR4 expression levels in cells with intrinsically trastuzumab-resistant cells compared to trastuzumab-sensitive cells. Upregulation of CXCR4 expression was found in each of the acquired TR cell lines compared to their parental cells. Dysregulation of CXCR4 significantly enhanced mammosphere formation and cell invasion (P < 0.001, respectively). SDF-1α induced cell invasion and clumping. Down-regulation of CXCR4 with shRNA significantly increased trastuzumab induced–antibody-dependent cellular cytotoxicity (2.17 folds of control cells, P < 0.01). Targeting CXCR4 with its approved inhibitor AMD3100 significantly decreased mammosphere formation and invasion of HER2+BC with TR (P < 0.01; P < 0.0001 respectively).

Conclusion: Our results suggest that the SDF-1-CXCR4 axis plays a critical role in resistance to trastuzumab. Targeting CXCR4 signaling may lead to novel combinational therapies to overcome intrinsic or acquired resistance to trastuzumab in advanced HER2+BC, including postulated effects of trastuzumab on signal transduction, differentiation and immune activation.

Citation Format: Liu S, Xie SM, Yang-Kolodji G, Tripathy D. Targeting the tumor microenvironment by CXCR4 inhibition to abrogate trastuzumab resistance in HER2-positive breast cancer [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P5-03-04.

Abstract P2-13-03: The impact of neratinib with or without anti-diarrheal prophylaxis on health-related quality of life in HER2+ early-stage breast cancer: Analyses from the ExteNET and CONTROL trials

Background: Neratinib is an irreversible pan-HER tyrosine kinase inhibitor. ExteNET, a randomized placebo-controlled phase III study, showed that neratinib given for 12 months after trastuzumab-based adjuvant therapy significantly improved 2-year (HR 0.67; 95% CI 0.50–0.91; p=0.0091) and 5-year (HR 0.73; 95% CI 0.57-0.92; p=0.008) iDFS in pts with early-stage HER2+ breast cancer. Anti-diarrheal prophylaxis was not mandated by protocol; grade 3/4 diarrhea occurred in 40% of pts with a median cumulative duration of 5 days. The phase II CONTROL study was initiated to investigate the effectiveness of various prophylactic regimens in the prevention of neratinib-associated diarrhea. Loperamide (L) alone or in combination with add-on agents targeting underlying inflammation [i.e. budesonide (BUD)] or bile acid malabsorption [i.e. colestipol (COL)] were tested. We report longitudinal HRQoL findings from both ExteNET and CONTROL.

Methods: Pts with early-stage HER2+ breast cancer who had received trastuzumab-based adjuvant therapy were eligible for both studies. In ExteNET, pts received neratinib or placebo for 12 months. In CONTROL, pts received neratinib for 13 x 28-day cycles combined with L, L + BUD or L + COL for 1 or 2 cycles (see table for schedules). HRQoL was assessed using Functional Assessment of Cancer Therapy–Breast (FACT-B), v4.0, at baseline, months 1, 3, 6, 9, 12 (ExteNET) or baseline, cycles 2, 4, 7, 10, 13 (CONTROL). Changes in scores from baseline were considered to be clinically meaningful if greater than the lowest estimate for an 'important difference' (ID) reported in the literature. Evaluable pts were required to have HRQoL assessments at baseline and at least 1 post-baseline. ClinicalTrials.gov: NCT00878709 (ExteNET); NCT02400476 (CONTROL).

Results: HRQoL findings are summarized in the table. Hospitalization rates due to diarrhea: 1.5% (neratinib + L), 0% (other cohorts) in CONTROL; and 1.4% (neratinib), 0.1% (placebo) in ExteNET.

  Mean change from baselineStudyCohort/GroupM1M3M6M9M12 FACT-B TOTAL (ID range: 7–8 points)CONTROLN + La,b (N=40)–3.8–4.5–1.5–2.5–3.3 N + L + BUDa,b,c (N=62)–6.0–4.9–1.6–3.6–4.5 N + L + COLa,b,d (N=125)–3.8–2.0–4.0–4.6–3.6 N + L prn + COLa,d (N=85)–1.8–1.54.0e––ExteNETN + L prna (N=1124)–4.6–3.4–3.5–3.3–3.7 P (N=1188)–1.7–3.5–2.9–2.9–2.8 FACT-B PWB (ID range: 2–3 points)CONTROLN + La,b (N=40)–4.0–2.3–1.9–2.4–2.3 N + L + BUDa,b,c (N=62)–3.2–2.1–1.4–1.7–1.7 N + L + COLa,b,d (N=125)–2.8–2.0–2.4–2.5–2.4 N + L prn + COLa,d (N=85)–2.8–1.80.0e––ExteNETN + L prna (N=1124)–2.9–1.9–1.7–1.6–1.5 P (N=1188)–0.6–0.8–0.7–0.6–0.4C, cycle; L, loperamide; M, month; N, neratinib; prn, as needed; PWB, physical well-being. CONTROL cut-off: 1 May 2018. aN 240 mg qd for 13 x 28d cycles or 12 months; bL 4 mg, then 4 mg tid d1-14, then 4 mg bid d15-28 or d15-56, then prn; cBUD 9 mg qd d1-28; dCOL 2 g qd d1-28; en=1.

Conclusions: Adjuvant neratinib with or without anti-diarrheal prophylaxis was associated with small decreases in HRQoL. With the exception of the FACT-B PWB subscale, HRQoL changes did not reach clinically meaningful thresholds. Follow-up in CONTROL is ongoing.

Citation Format: Delaloge S, Hurvitz S, Chan N, Bose R, Jankowitz RC, Thirlwell M, Láng I, ten Tije A, Trudeau M, Osborne CR, Shen Z-Z, Lalla D, Xu F, Hunt D, Olek E, Tripathy D, Rugo HS, Chien J, Chan A, Barcenas CH. The impact of neratinib with or without anti-diarrheal prophylaxis on health-related quality of life in HER2+ early-stage breast cancer: Analyses from the ExteNET and CONTROL trials [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P2-13-03.

Abstract P2-07-03: Refining neoadjuvant predictors of three year distant metastasis free survival: Integrating volume change as measured by MRI with residual cancer burden

Background: Patients achieving a pathologic complete response (pCR) following neoadjuvant therapy have significantly improved event-free survival relative to those who do not; and pCR is an FDA-accepted endpoint to support accelerated approval of novel agents/combinations in the neoadjuvant treatment of high risk early stage breast cancer. Previous studies have shown that recurrence risk increased with increasing burden of residual disease (as assessed by the RCB index). As well, these studies suggest that patients with minimum residual disease (RCB-I class) also have favorable outcomes (comparable to those achieving a pCR) within high risk tumor subtypes. In this study, we assess whether integrating RCB with MRI functional tumor volume (FTV), which in itself is prognostic, can improve prediction of distant recurrence free survival (DRFS); and identify a subset of patients with minimal residual disease with comparable DRFS as those who achieved a pCR. Imaging tools can then be used to identify the subset that will do well early and guide the timing of surgical therapy.

Method: We performed a pooled analysis of 596 patients from the I-SPY2 TRIAL with RCB, pre-surgical MRI FTV data and known follow-up (median 2.5 years). We first assessed whether FTV predicts residual disease (pCR or pCR/RCB-I) using ROC analysis. We applied a power transformation to normalize the pre-surgical FTV distribution; and assessed its association with DRFS using a bi-variate Cox proportional hazard model adjusting for HR/HER2 subtype. We also fitted a bivariate Cox model of RCB index adjusting for subtype; and assessed whether adding pre-surgical FTV to this model further improves association with DRFS using a likelihood ratio (LR) test. For the Cox modeling, penalized splines approximation of the transformed FTV and RCB index with 2 degrees of freedom was used to allow for non-linear effects of FTV and RCB on DRFS.

Result: Pre-surgical MRI FTV is significantly associated with DRFS (Wald p<0.00001), and more effective at predicting pCR/RCB-I than predicting pCR alone (AUC: 0.72 vs. 0.65). Larger pre-surgical FTV remains associated with worse DRFS adjusting for subtype (Wald p <0.00001). The RCB index is also significantly associated with DRFS adjusting for subtype (Wald p<0.00001). Adding FTV to a model containing RCB and subtype further improves association with DRFS (LR p=0.0007). RCB-I patients have excellent DRFS (94% at 3 years compared to 95% in the pCR group). Efforts are underway to identify an optimal threshold for dichotomizing pre-surgical FTV and FTV change measures for use in combination with pCR/RCB-I class to generate integrated RCB (iRCB) groups as a composite predictor of DRFS.

Conclusion: Pre-surgical MRI FTV is effective at predicting minimal residual disease (RCB0/I) in the I-SPY 2 TRIAL. Despite the association between FTV and RCB, FTV appears to provide independent added prognostic value (to RCB and subtype), suggesting that integrating MRI volume measures and RCB into a composite predictor may improve DRFS prediction.

Citation Format: Hylton NM, Symmans WF, Yau C, Li W, Hatzis C, Isaacs C, Albain KS, Chen Y-Y, Krings G, Wei S, Harada S, Datnow B, Fadare O, Klein M, Pambuccian S, Chen B, Adamson K, Sams S, Mhawech-Fauceglia P, Magliocco A, Feldman M, Rendi M, Sattar H, Zeck J, Ocal I, Tawfik O, Grasso LeBeau L, Sahoo S, Vinh T, Yang S, Adams A, Chien AJ, Ferero-Torres A, Stringer-Reasor E, Wallace A, Boughey JC, Ellis ED, Elias AD, Lang JE, Lu J, Han HS, Clark AS, Korde L, Nanda R, Northfelt DW, Khan QJ, Viscusi RK, Euhus DM, Edmiston KK, Chui SY, Kemmer K, Wood WC, Park JW, Liu MC, Olopade O, Tripathy D, Moulder SL, Rugo HS, Schwab R, Lo S, Helsten T, Beckwith H, Haugen PK, van't Veer LJ, Perlmutter J, Melisko ME, Wilson A, Peterson G, Asare AL, Buxton MB, Paoloni M, Clennell JL, Hirst GL, Singhrao R, Steeg K, Matthews JB, Sanil A, Berry SM, Abe H, Wolverton D, Crane EP, Ward KA, Nelson M, Niell BL, Oh K, Brandt KR, Bang DH, Ojeda-Fournier H, Eghtedari M, Sheth PA, Bernreuter WK, Umphrey H, Rosen MA, Dogan B, Yang W, Joe B, I-SPY 2 TRIAL Consortium, Yee D, Pusztai L, DeMichele A, Asare SM, Berry DA, Esserman LJ. Refining neoadjuvant predictors of three year distant metastasis free survival: Integrating volume change as measured by MRI with residual cancer burden [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P2-07-03.

Abstract P2-01-03: Lipocalin 2 promotes inflammatory breast cancer tumorigenesis and skin invasion

Background: Inflammatory breast cancer (IBC) is the most lethal form of primary breast cancer and accounts for a significant 10 % of breast cancer deaths in the USA owing to its aggressive proliferation and metastasis, and a lack of effective therapeutic options. Unraveling the underlying mechanisms of growth and metastasis of this aggressive disease could lead to effective therapeutic strategies for an improved outcome in IBC patients. We recently generated in vitro and in vivo IBC models for brain metastasis studies [Debeb et al. JNCI, 2016] and observed an upregulation of Lipocalin 2 (LCN2), a small, secreted iron-trafficking protein which plays a significant role in immune and inflammatory responses and the promotion of malignant progression. The purpose of this study was to investigate the function of LCN2 in IBC tumorigenesis and metastasis.

Methods: Stable knockdown (KD) of LCN2 in IBC cell lines was achieved with lentiviral vectors. Proteomic and gene expression profiling were performed using RPPA and Affymetrix Clariom D microarray. For in vivo studies, control and LCN2 KD IBC cells were transplanted into the cleared mammary fat pad of SCID/Beige mice. Tumor-skin involvement was assessed visually during primary tumor growth and tumor excision. LCN2 gene expression levels in clinical samples were analyzed from the IBC Consortium as well as public data sets. LCN2 serum levels in IBC patients were measured using ELISA and were correlated with clinicopathological variables and outcome data.

Results: LCN2 gene expression is higher in IBC versus non-IBC patients (p=0.00036), independently of the molecular subtypes, and higher in more aggressive (TNBC and HER2+) than hormone receptor-positive subtypes (p<0.00001). LCN2 expression in patient tissues is correlated with reduced overall survival (p<0.00001) and metastasis-free survival (p=0.04) in non-IBC; however, LCN2 was not associated with overall survival in IBC patient serum samples. LCN2 expression was also significantly higher in IBC cell lines, in their culture media, and in brain metastasis sublines compared to non-IBC cell lines (p=0.004). In IBC cell lines, LCN2 KD reduced proliferation, colony formation, migration, and cancer stem cell properties. In vivo silencing of LCN2 in SUM149 cells inhibited primary tumor growth (p=0.001)and resulted in a well-differentiated tumor histology. Additionally, SUM149 LCN2 KD significantly reduced skin invasion/recurrence (LCN2 control vs LCN2 KD: 88 % vs 25 %, p=0.01) suggesting LCN2 is a mediator of tumorigenesis. Analysis of proteomics data showed changes in major signaling pathways including PI3K-Akt signaling and EGF/EGFR signaling pathways. Mechanistically, LCN2 depletion in SUM149 abrogated EGF-induced EGFR phosphorylation and ERK activation.

Conclusions: Our findings suggest that LCN2 may drive IBC tumor progression and skin invasion/recurrence potentially via the EGFR signaling pathway.Future studies will determine the role of LCN2 in metastasis and pinpoint the detailed mechanisms of LCN2-mediated IBC tumorigenesis and recurrence.

Citation Format: Villodre ES, Larson R, Hu X, Stecklein SR, Gomez K, Finetti P, Krishnamurthy S, Ivan C, Su X, Ueno NT, Van Laere S, Bertucci F, Tripathy D, Vivas-Mejía P, A Woodward W, Debeb BG. Lipocalin 2 promotes inflammatory breast cancer tumorigenesis and skin invasion [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P2-01-03.

Abstract P3-08-02: Withdrawn

This abstract was withdrawn by the authors.

Citation Format: Harano K, Wang Y, Masuda H, Lim B, Parinyanitikul N, Lee H-J, Seitz RS, Morris SW, Bailey DB, Hout DR, Rao A, Lucci A, Tripathy D, Krishnamurthy S, Ueno NT. Withdrawn [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P3-08-02.

Abstract P6-18-15: Ribociclib + endocrine therapy in hormone receptor-positive, HER2-negative advanced breast cancer: A pooled safety analysis

Background: In Phase III trials, ribociclib (RIB; cyclin-dependent kinase 4/6 inhibitor) + various endocrine therapy (ET) partners has demonstrated significantly prolonged progression-free survival vs placebo (PBO) + ET in patients (pts) with hormone receptor-positive (HR+), HER2-negative (HER2–) advanced breast cancer (ABC). Here we further evaluate the safety of RIB-based regimens of interest for the proposed indication (i.e. with a non-steroidal aromatase inhibitor [NSAI] or fulvestrant [FUL]) using pooled data from three Phase III trials (MONALEESA [ML]-2 [NCT01958021], -3 [NCT02422615], and -7 [NCT02278120]).

Methods: Postmenopausal pts with HR+, HER2– ABC received RIB (600 mg/day; 3-weeks-on/1-week-off) or PBO + letrozole (LET; 2.5 mg/day; ML-2 [no prior ET for ABC]) or FUL (500 mg, Days 1 and 15 of Cycle 1, then Day 1 of every cycle thereafter; ML-3; no or ≤1 prior line of ET for ABC]). Premenopausal pts (ML-7; no prior ET and ≤1 chemotherapy for ABC]) received RIB or PBO + anastrozole (1 mg/day)/LET (2.5 mg/day) + goserelin (3.6 mg every 28 days). Adverse events (AEs) were characterized per Common Terminology Criteria for Adverse Events v4.03; safety analyses included time to first event, duration of event, and rate of associated RIB/PBO discontinuations.

Results: Data for 1883 pts were pooled; 1065 pts received RIB + ET and 818 pts received PBO + ET (median exposure to study treatment: 17 and 13 months, respectively). Exposure-adjusted incidence rates for AEs of special interest were 561 and 131 per 100 pt-years in the RIB and PBO arms, respectively. The most common all-causality Grade 3/4 AEs (≥10% in any arm; RIB vs PBO) were neutropenia (59% vs 2%), leukopenia (18% vs 1%), and hypertension (13% vs 13%). A new Fridericia's corrected QT interval (QTcF) >480 ms occurred in (n/N) 52/1054 (5%) vs 11/814 (1%) pts in the RIB vs PBO arms; a new QTcF >500 ms occurred in 14/1054 (1%) vs 1/814 (<1%) pts. Median time to first event for Grade ≥2 neutropenia, elevated alanine aminotransferase (ALT) and/or aspartate aminotransferase (AST), and QTc prolongation in the RIB arm was 2, 12, and 2 weeks, respectively; median duration of first Grade ≥2 event was 4, 4, and 2 weeks. In the RIB arm vs PBO arms, 7% vs 3% of pts discontinued study treatment due to AEs; common all-grade AEs leading to RIB/PBO discontinuation (≥2% in any arm) were elevated ALT (4% vs <1%) and elevated AST (2% vs 1%). Discontinuation due to QT prolongation occurred in 4 pts in the RIB arm and 2 in the PBO arm (both <1%). All-grade serious AEs occurred in 25% of pts in the RIB arm vs 15% of pts in the PBO arm.

Conclusions: RIB in combination with various ET partners continues to demonstrate a predictable and manageable tolerability profile across a broad population of pts with HR+, HER2– ABC.

Citation Format: Burris HA, Chan A, Im S-A, Chia S, Tripathy D, Esteva FJ, Campone M, Bardia A, Kong O, Bao W, Diaz-Padilla I, Rodriguez Lorenc K, Yardley DA. Ribociclib + endocrine therapy in hormone receptor-positive, HER2-negative advanced breast cancer: A pooled safety analysis [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P6-18-15.

Abstract P5-03-06: Overcoming MEK inhibitor resistance in triple-negative breast cancer by targeting myeloid cell leukemia-1 (MCL1), an anti-apoptotic protein

Background: Triple-negative breast cancer (TNBC), which affects over 170 000 women worldwide every year, is considered the most arduous to treat subtype of breast cancer. With no targeted therapy, high rates of drug resistance and rapid metastasis, TNBC carries a poor prognosis. The MEK-ERK-MAPK signaling cascade is known to play a role in numerous cancers. Despite the lack of activating Ras/MAPK mutations in breast cancer, transcriptional signatures of this pathway are prevalent in TNBC. Our previous work showed that TNBC patients with tumors overexpressing ERK2 had a lower overall survival rate than did patients with low-ERK2-expressing tumors. MEK inhibitors selumetinib (AZD6244) and pimasertib (AS703026) are active in preclinical models, but not as single agents in the clinic. Using a synthetic lethal siRNA screen, we identified myeloid cell leukemia-1 (MCL1) as a potential contributor to selumetinib resistance. Mcl-1 is an anti-apoptotic protein that is highly amplified in numerous human cancers. It is associated with cell immortalization, transformation, and chemoresistance. Patients with TNBC tumors expressing high levels of Mcl-1 have lower overall survival and distant-metastasis-free survival rates. We hypothesized that Mcl-1 promotes MEK inhibitor resistance in TNBC.

Methods/Results: To model MEK inhibitor resistance, we established selumetinib- and pimasertib-resistant clones of SUM-149 and MDA-MB-231 TNBC cells by continuous exposure to increasing concentrations of inhibitors over a six month period. We confirmed the onset of MEK resistance by demonstrating that resistant cells, in comparison to the parental cells, exhibited no change in cell proliferation upon treatment with the MEK inhibitors. Resistant cells also displayed more effective cell migration and mammosphere formation than parental cells, suggesting a higher fraction of tumor-initiating cells.

We found Mcl-1 to be highly expressed in 83% (15 of 18) of TNBC cell lines but only 30% (3 of 10) of other breast cancer cell lines. Resistant cells had higher levels of Mcl-1 than did parental cells. To determine whether Mcl-1 is required for MEK sensitivity, we treated parental and resistant cells with either selumetinib or pimasertib together with S63845, a highly specific Mcl-1 inhibitor. The Mcl-1 inhibitor restored MEK sensitivity in both resistant cell lines. After treatment with the Mcl-1 inhibitor, the resistant SUM-149 and MDA-MB-231 cells had similar cell proliferation rates to those of their parental counterparts. Similar studies were done using an siRNA against Mcl-1.

Conclusion: Our data demonstrate that Mcl-1 may promote TNBC resistance to MEK inhibitors and that Mcl-1 is a promising target for combination therapy. We will continue to explore the mechanisms of MEK inhibitor resistance by screening for additional genes/pathways involved. Our long-term goal is to design rational combination approaches to counteract the emergence of resistance by using novel molecularly targeted therapeutics.

Citation Format: Gagliardi M, Chauhan G, Pitner MK, Iles L, Qi Y, Pusztai L, Tripathy D, Bartholomeusz G, Bartholomeusz C. Overcoming MEK inhibitor resistance in triple-negative breast cancer by targeting myeloid cell leukemia-1 (MCL1), an anti-apoptotic protein [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P5-03-06.

Abstract P3-10-23: Changes in the expression of HER2 and other genes in HER2-positive metastatic breast cancer induced by treatment with ado-trastuzumab emtansine and/or pertuzumab/trastuzumab

Background: Although tremendous progress has been achieved with targeted therapy for HER2-positive (HER2+) metastatic breast cancer, most advanced tumors eventually develop resistance. Improving our understanding of mechanisms of resistance to anti-HER2 therapy is needed to develop new therapeutic approaches. The purpose of this study was to identify the mechanisms of resistance to treatment with ado-trastuzumab emtansine (T-DM1) and/or taxane/pertuzumab/trastuzumab (TPH).

Methods: In our preclinical analysis, HER2+ cell lines resistant to treatment with T-DM1 (n=5), and pertuzumab/trastuzumab (n=3) were generated. HER2 expression in the original and resistant cell lines was compared using Western blot, and HER2 gene amplification was compared in them using fluorescence in situ hybridization (FISH) and a Droplet Digital Polymerase Chain Reaction HER2 copy-number-validation assay. In our clinical analysis, nine patients with HER2+ metastatic breast cancer who had progressed on T-DM1 and/or TPH were enrolled. Patients underwent biopsies following treatment with T-DM1 and/or TPH. Targeted next-generation sequencing was performed using the FoundationOne® assay (Foundation Medicine, Inc.) to identify gene alterations. Also, the HER2 expression before and after the therapy was compared using immunohistochemistry and/or FISH.

Results: In preclinical analysis, HER2 expression/amplification by Western blot and gene copy-number analysis was significantly decreased in T-DM1–resistant cell lines (four of five cell lines; P < 0.01) but not in pertuzumab/trastuzumab-resistant cell lines (none of three cell lines). In clinical analysis, the patients' median age was 54 years (range, 45-77 years), and five patients (56%) were ER+. Five patients (56%) received first-line anti-HER2 therapy, and four patients (44%) received two lines of anti-HER2 therapy prior to enrollment. We observed loss of HER2 expression in four of nine patients (44%) after undergoing anti-HER2 therapy. After receiving TPH, one of eight patients (13%) lost HER2 positivity according to FISH. In contrast, after T-DM1, three of four tested patients (75%) lost HER2 amplification by FISH. As for next-generation sequencing, we analyzed seven samples: three after treatment with TPH and four after treatment with T-DM1. In four of these samples (57%), we observed loss of HER2 amplification: one after treatment with TPH and three after treatment with T-DM1. TP53 mutations were seen in all patients. Additionally, we observed TOP2A and MCL1 amplification in two patients with ERBB2 amplificationand AKT1 amplification in one patient with ERBB2 amplification loss.

Conclusions: We show for the first time that T-DM1–resistant breast cancer cells lose HER2 expression and amplification. Additionally, we observed loss of HER2 expression in patient samples following treatment with HER2 targeted therapy. Further study of resistant tumor samples is required to understand the impact of HER2 loss on outcomes. For the time being, repeating biopsy analysis of a metastatic site after treatment with T-DM1 to determine the HER2 expression status is reasonable, and it may increase the efficacy of future anti-HER2 therapy.

Citation Format: Kida K, Lee J, Liu H, Lim B, Murthy RK, Sahin AA, Tripathy D, Ueno NT. Changes in the expression of HER2 and other genes in HER2-positive metastatic breast cancer induced by treatment with ado-trastuzumab emtansine and/or pertuzumab/trastuzumab [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P3-10-23.

Abstract P6-17-04: 3-year relapse-free survival of stage II-III HER2-neu positive breast cancer treated with pertuzumab and trastuzumab-containing neoadjuvant therapy compared to trastuzumab-containing therapy

Background: Pertuzumab (P) in combination with trastuzumab (H) based chemotherapy is FDA-approved as a standard neoadjuvant treatment for patients with clinical stage II-III HER2-positive (HER2+) breast cancer (BC). The goal of this study was to evaluate the pathologic complete response (pCR) rate for neoadjuvant HP-containing regimens compared to H-containing regimens and report the 3-year relapse-free survival (RFS) for patients who had a pCR compared to those with residual disease (RD).

Methods: All patients with stage II-III non-inflammatory HER2+ BC who received neoadjuvant H-containing or HP-containing therapy and underwent definitive breast and axillary surgery were identified from 2005 to 2016 through an institutional database. Medical records were examined for patient demographics, breast cancer stage, pathology results, surgical outcomes, and treatment details. pCR was defined as ypT0/is, ypN0. RFS was defined as the interval from surgery to date of last followup or death from any cause. Descriptive statistics, Cox proportional hazards, and Kaplan-Meier estimates were used for statistical analysis.

Results: Patient characteristics and results by pCR or RD status are shown in the table below. The median age was 51 (22-84) years for the HP group and 50 (21-87) years for the H group. The median follow-up time was 1.9 (0-4.2) years for the HP group and 5.3 (0.1-12) years for the H group. For the HP group, the 3-year RFS was 98% (95% CI: 95, 100) for the pCR group and 90% (95% CI: 83, 97) for the RD group; HR 0.17 (0.04, 0.82), p=0.012. For the H group, the 3-year RFS was 91% (95% CI: 88,94) for the pCR group and 75% (95% CI: 71-79) for the RD group; HR 0.31 (0.22, 0.44), p<0.0001. Among the 520 patients who achieved pCR and the 502 patients who had RD, the effect of HP vs. H was statistically significant (pCR: HR 0.24 (0.06, 1.00); p=0.015) (no pCR: HR 0.46 (0.22, 0.94); p=0.017).

Conclusion: Patients who achieve pCR have an improved 3-year RFS compared to patients who have RD. Treatment with HP-containing neoadjuvant regimens is associated with a high 3-year RFS.

VariableHP (n=215)H (n=807)  pCR n=121RD n=94pCR n=399RD n= 408Age at Diagnosis<5043%46%46%51% ≥5057%54%54%49%Menopausal StatusPremenopausal46%50%53%57% Postmenopausal54%50%47%43%Clinical Stage at DiagnosisIIA40%29%34%29% IIB29%31%23%28% IIIA14%15%17%16% IIIB0%5%5%9% IIIC17%20%21%18%Clinical Nodal StatusNode (+)63%76%69%73% Node (-)37%24%31%27%Nuclear Grade1II25%32%22%28% III75%65%78%72%HR statusHR(+)52%74%52%67% HR(-)48%26%48%33%Adjuvant therapyTrastuzumab88%80%100%100% Trastuzumab and Pertuzumab3%5%0%0% Unknown9%15%20%0%11 patient in the HP pCR group had nuclear grade 1; 2 patients in the HP RD group had nuclear grade 1 tumors 2 2 patients received adjuvant TDM-1 on the NSABP B50 protocol

Citation Format: Murthy RK, Raghavendra AS, Hess KR, Barcenas CH, Lim B, Moulder SL, Giordano SH, Mittendorf EA, Thompson A, Ueno NT, Valero V, Litton JK, Tripathy D, Chavez-Macgregor M. 3-year relapse-free survival of stage II-III HER2-neu positive breast cancer treated with pertuzumab and trastuzumab-containing neoadjuvant therapy compared to trastuzumab-containing therapy [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P6-17-04.

Abstract P3-06-01: Clonal evolution and heterogeneity in breast tumors treated with neoadjuvant HER2-targeted therapy

Background: Understanding to what extent a breast tumor's genetic composition may change over the course of a few months of neoadjuvant therapy has implications for optimal therapeutic approach. However, genomic changes observed across treatment may result from either treatment-induced clonal evolution or geographically disparate sampling of a heterogeneous tumor. We sought to characterize the geographic heterogeneity in primary breast tumors, and to incorporate this information into analysis of clonal evolution with neoadjuvant therapy.

Methods: We assembled the largest cohort to date of multi-region (n=2-3) whole-exome sequenced (WES) or whole-genome sequenced untreated primary breast tumors with matched normal and adequate tumor purity for analysis: four tumors with data generated for this study and five tumors compiled from three previous studies. We also generated the first cohort of multi-region (n=2-6) WES breast tumors post-neoadjuvant HER2-targeted therapy and chemotherapy, sequencing one region from a pre-treatment diagnostic specimen, multiple regions from the post-treatment surgical specimen, and matched normal for five HER2+ breast tumors that did not achieve a pathologic complete response. We used an agent-based model of spatial tumor growth to investigate whether the mutational patterns we observed with treatment were consistent with pre-existing heterogeneity or treatment-induced selection.

Results: In untreated primary breast tumors, on average 30% (range 1-70%) of apparently clonal mutations from a single region were absent or rare in a second, spatially disparate region (high-frequency regional, or HFR). Intra-tumor heterogeneity was similar post-treatment (HFR 28%, range 10-54%), and was higher in breast tumors than in previously analyzed colon, brain, lung, and esophageal tumors. Simulation studies confirmed that with high heterogeneity as observed in breast tumors, analysis of one pre-treatment and one post-treatment region could not distinguish treatment-induced clonal evolution from pre-existing heterogeneity; however, obtaining at least two post-treatment regions allowed for detection of clonal shifts with treatment. Analysis of multi-region data revealed that clonal replacement occurred with neoadjuvant therapy in two of the five tumors. Candidate causes of therapeutic resistance included amplifications in CCND1, ERBB4, and MYC in one subclone, and functional protein-altering mutations in ERCC2, SMO, and WT1 in another. Mathematical modeling suggested that these putative resistant subclones comprised 0.02-12.5% of the overall pre-treatment cell population, substantially larger than previous estimates of resistant tumor clone size.

Conclusions: WES data from multiple regions of untreated and treated primary breast tumors revealed considerable heterogeneity that remained present throughout treatment with chemotherapy and HER2-targeted therapy, even while major clonal sweeps took place in a minority of tumors. Obtaining at least two samples for analysis from breast tumors post-neoadjuvant therapy may reveal the tumor's evolutionary path and, especially as increasing numbers of molecular and immune therapeutic targets are identified, inform new clinical strategies.

Citation Format: Caswell-Jin JL, McNamara K, Reiter JG, Sun R, Hu Z, Ma Z, Suarez CJ, Tilk S, Raghavendra A, Forte V, Chin S-F, Bardwell H, Provenzano E, Caldas C, Lang J, West R, Tripathy D, Press MF, Curtis C. Clonal evolution and heterogeneity in breast tumors treated with neoadjuvant HER2-targeted therapy [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P3-06-01.

Abstract P4-02-05: Apocrine morphology and LAR molecular subtype predict prognosis of TNBC patients with residual disease after neoadjuvant chemotherapy

Background: TNBC molecular subtype classification updated by Lehmann et al. includes 4 subtypes: basal-like 1 and 2 (BL1), (BL2), mesenchymal (M), and luminal androgen receptor (LAR), and as a modifier of these subtypes, an Immunomodulatory (IM) gene expression signature. However, molecular subtypes have not been linked to morphological features of TNBC. Apocrine carcinoma has been proposed as a TNBC category that expresses androgen receptor. LAR-subtype TNBC has a poor response to neoadjuvant systemic therapy (NST). We hypothesized that defining the apocrine-featured TNBC by morphology and molecular subtype predict the prognosis of patients with residual disease after NST. Methods: We created the Pan-Pacific TNBC Consortium dataset, which contains paired samples of matched pre and post-NST TNBC tumors from 4 institutions. All patients received NST and didn't have a pathological complete response (pCR). Three pathologists examined hematoxylin and eosin-stained slides of 86 pre-NST samples and determined (1) the presence of apocrine differentiation, (2) the level of tumor-infiltrating lymphocytes (TILs), (3) the histological grade (HG), and (4) the rate of necrosis. These morphological features were compared among the subtypes. For a sample to be considered apocrine positive, apocrine differentiation had to be identified by 2 or more pathologists. Fisher's exact test was used to test the association of subtypes and morphological features. The log-rank test was used to compare disease-free survival (DFS). Results: Twelve of 24 (50%) apocrine-positive tumor samples were LAR subtype, and12 of 17 (70%) LAR-subtype tumor samples exhibited apocrine differentiation. The other subtypes showed following: BL1, 11/44 (25%); BL2, 0/7 (0%); M, 1/10 (10%); unclassified, 0/8 (0%). The median follow-up time was 22 months. In all populations, 2-year DFS rates were higher in patients with apocrine-positive tumors than in those whose tumors did not exhibit apocrine differentiation (P = .027; 2-year DFS, 85% vs 54%). The LAR subtype was also associated with lower HG, although LAR tumors had a similar prognosis to the other subtypes. In the combined analysis of subtypes and apocrine differentiation, patients with apocrine-positive LAR tumors had a higher 2-year DFS rate than did those with apocrine-negative LAR tumors (P = .044; 2-year DFS, 88% vs. 30%). However, patients with apocrine-positive BL1 tumors had no better DFS than did those with apocrine-negative BL1 tumors (P = .133). TIL levels and the presence of the IM signature were positively associated (P = .01), and apocrine differentiation positivity tended to be negatively associated with TIL level (P = .06). Neither TIL level nor IM signature was associated with survival. Conclusion: Apocrine differentiation was associated with the LAR subtype of TNBC and better prognosis in patients who did not have a pCR. The LAR subtype alone did not predict DFS; however, LAR tumors with apocrine differentiation had a better prognosis than did LAR tumors without apocrine differentiation. Using a combination of morphologic and genomic testing may be helpful in determining the prognosis of patients with apocrine-positive TNBC tumors who have residual disease after NST.

Citation Format: Masuda H, Miura S, Harano K, Wang Y, Hirota Y, Matsunaga Y, Lim B, Lucci A, Parinyanitikul N, Lee HJ, Gong G, Rao A, Seitz RS, Morris SW, Hout DR, Nakamura S, Tripathy D, Harada O, Krishnamurthy S, Ueno NT. Apocrine morphology and LAR molecular subtype predict prognosis of TNBC patients with residual disease after neoadjuvant chemotherapy [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P4-02-05.

Abstract P1-18-04: CTCs and SUV to predict the efficacy of the bone-specific radiopharmaceutical agent radium-223 dichloride combined with hormonal therapy for hormone receptor-positive bone-dominant breast cancer metastasis

Background: Radium-223 dichloride (Ra-223) is a targeted alpha particle-based radiotherapeutic that has a localized cytotoxic effect on bone metastases. We sought to determine whether the circulating tumor cell (CTC) count and the presence of CTCs in epithelial-mesenchymal transition (EMT-CTCs) along with the standardized uptake value (SUV) on positron emission tomography-computed tomography (PET/CT) scans predict the efficacy of combined Ra-223 and hormonal therapy in patients with hormone receptor (HR)-positive bone-dominant metastatic breast cancer.

Patients and Methods: In this single-center phase 2 study (NCT02366130), 36 patients received Ra-223 (55 kBq/kg intravenously) on day 1 and then every 4 weeks for six cycles. Patients also received a standard care endocrine monotherapy. One non-bone metastatic site was allowed. The number of prior endocrine therapies was not limited and one prior chemotherapy was allowed for metastasis. Response was evaluated using the PET Response Criteria in Solid Tumors (PERCIST) with PET/CT at baseline, 6 and 9 months (mo) later. The CTC count (CellSearch) and the presence of EMT-CTCs (AdnaTest) was determined at baseline, 6 and 9 mo later. Progression-free survival (PFS) time was calculated to evaluate efficacy.

Results: Seven patients (20%) had a non-bone metastatic site. The median number of prior therapies for metastasis was 1 (range, 0-4). Six patients (17%) received chemotherapy. The median CTC count at baseline was 4 (range, 0-306). Only four patients (11%) were positive for EMT-CTCs at baseline. The median follow-up time was 14.7 mo (95% confidence interval [CI], 13.2 mo-not reached [NR]). The disease control rate at 9 mo was 46% in 33 patients who reached 9 mo or progressed up to 9 mo. The tumor response rate at 6 mo was 52% (complete/partialresponse rate; 22/30 %) in 27 patients whose disease was evaluable using PERCIST. The SUV on PET/CT decreased significantly at 6 and 9 mo after baseline (average decreases of 1.5 (p=0.0004) and 2.5 (p=0.0054), respectively). The median PFS duration was 7.4 mo (95% CI, 4.8 mo-NR). The median bone PFS was 16 mo (95% CI, 7.3 mo-NR). Patients with bone-only metastasis (N=28, 80%) had a significantly longer median PFS duration than did patients with non-bone metastases at baseline (N=7, 20%) (13.8 mo versus 4.5 mo; p=0.017). Patients without prior treatment (N=12, 34%) tended to have longer median PFS durations than did those who underwent prior treatment (N=23, 66%) (16.8 mo versus 4.8 mo; p=0.1865). Also, patients with <5 CTCs at baseline (N=19, 54%) tended to have longer median PFS durations than did those with ≥5 CTCs (N=16, 46%) (13.8 mo versus 4.8 mo; p=0.1277). EMT-CTCs status did not predict efficacy.

Conclusions: Bone-only metastatic breast cancer and SUV suppression by Ra-223 are predictive of efficacy. Patients with baseline <5 CTC count tended to have better outcomes than did those with ≥5 CTCs. Combined treatment with Ra-223 and a hormonal agent is especially effective at controlling bone metastasis in patients with HR-positive breast cancer. Bone-only metastatic disease and CTC count should be factored in future clinical trial designs.

Citation Format: Ueno NT, Tahara RK, Reuben JM, Gao H, Saigal B, Fujii T, Lucci A, Ibrahim NK, Damodaran S, Shen Y, Liu DD, Hortobagyi GN, Tripathy D, Lim B, Chasen BA. CTCs and SUV to predict the efficacy of the bone-specific radiopharmaceutical agent radium-223 dichloride combined with hormonal therapy for hormone receptor-positive bone-dominant breast cancer metastasis [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P1-18-04.

Abstract P1-15-02: Withdrawn

This abstract was withdrawn by the authors.

Citation Format: Schwab R, Clark A, Yau C, Wolf D, Chien AJ, Majure M, Ewing C, Wallace A, Roesch E, Helsten T, Forero A, Stringer-Reasor E, Vaklavas C, Nanda R, Jaskowiak N, Boughey J, Haddad T, Han H, Lee C, Albain K, Isaacs C, Elias A, Ellis E, Shah P, Lang J, Lu J, Tripathy D, Kemmer K, Yee D, Haley B, Korde L, Edmiston K, Northfelt D, Viscusi R, Khan Q, I-SPY 2 Consortium, Symmans WF, Perlmutter J, Hylton N, Rugo H, Melisko M, Wilson A, Singhrao R, Asare S, van't Veer L, DeMichele A, Berry D, Esserman L. Withdrawn [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P1-15-02.

Abstract OT3-05-04: Phase II study of atezolizumab, cobimetinib, and eribulin in patients with recurrent or metastatic inflammatory breast cancer (IBC)

Background: IBCs that do not completely respond to chemotherapy often have dysregulated immune pathways, and novel therapies are needed to improve outcomes in recurrent/metastatic disease. One-third of IBCs express the atezolizumab target PD-L1, and cobimetinib increases PD-L1 expression; thus, we hypothesize that atezolizumab and cobimetinib may act synergistically in IBC. The FDA-approved agent eribulin is active in IBC and has anti-stem cell activity and can reverse the IBC phenotype of epithelial-to-mesenchymal transition. Hence the use of eribulin as a chemotherapy backbone in combination with other novel agents is well justified.

Trial Design: This single-arm, open-label trial is enrolling patients with recurrent IBC or de novo metastatic IBC that has progressed on at least 1 line of standard chemotherapy. During a 4-week pharmacodynamic window, patients have an upfront biopsy, receive atezolizumab and cobimetinib treatment for 4 weeks, and have a second biopsy. Triple-combination treatment then commences, with standard eribulin dosing. After 4 cycles of eribulin, patients receive maintenance targeted therapy until disease progression or intolerable toxicity.

Eligibility Criteria: Patients with metastatic IBC of any molecular subtype must have measurable disease (per RECIST 1.1) amenable to biopsy. Patients with HER2+ disease must have received both pertuzumab and T-DM1. Patients with treated stable brain metastases are allowed. Patients must have recovered from the acute effects of any prior therapies and have adequate hematologic, organ, and cardiac function. Patients with autoimmune diseases or a history of pneumonitis are ineligible.

Specific Aims: The primary objective is to determine the overall response rate (ORR) of the combination therapy. Secondary objectives include determining the safety and tolerability, clinical benefit rate, response duration, progression-free survival, 2-year overall survival rate and predictive biomarker analyses.

Statistical Methods: The trial will enroll up to 9 patients in its phase I/safety lead-in portion and up to 33 patients total. A Bayesian optimal interval design is used to efficiently determine the maximum tolerated cobimetinib dose in phase I. Patients start cobimetinib at the FDA-approved dose of 60 mg/day with a target toxicity rate is 0.3. Phase II will enroll 24 patients to determine the efficacy of the triple-combination therapy. The historical ORR in metastatic IBC is 10%; our sample size provides 80% power to detect an ORR improvement to 25%.

Accrual: The trial has enrolled 7 patients since its start in August 2017.

Citation Format: Alexander A, Marx AN, Reddy SM, Reuben JM, Le-Petross HC, Lane D, Huang ML, Krishnamurthy S, Gong Y, Gombos DS, Patel N, Tung CI, Allen RC, Kandl TJ, Wu J, Liu S, Patel AB, Futreal A, Wistuba I, Layman RM, Valero V, Tripathy D, Ueno NT, Lim B. Phase II study of atezolizumab, cobimetinib, and eribulin in patients with recurrent or metastatic inflammatory breast cancer (IBC) [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr OT3-05-04.

Abstract P4-08-06: Impact of molecular subtypes on long-term outcomes in triple-negative breast cancer (TNBC) patients treated with adjuvant AC chemotherapy on SWOG S9313

Introduction: TNBC is heterogeneous disease with several molecularly defined subtypes (Lehman et al), each of which may be predictive of response to chemotherapy. TNBC molecular subtypes are associated with varied pathological responses to neoadjuvant chemotherapy. However, subtype specific long-term outcomes for TNBC patients treated with uniform adjuvant chemotherapy are not known.

Aims: To characterize long-term outcomes of TNBC molecular subtypes (TNBCtypes) in patients treated with adjuvant doxorubicin (A) and cyclophosphamide (C) on S9313

Methods: SWOG 9313 accrued 3,125 women with early stage breast cancer to two alternative dose schedules of AC with no difference in outcomes between the two arms (J Clin Oncol 2007). From this trial we identified 425 (14%) patients with centrally determined TNBC for whom tissue was available. Microarray profiling was performed on genomic RNA extracted from pre-treatment FFPE tissue. A 101-gene expression model which has shown to reproduce the classification provided by the original 2188-gene algorithm (Ring et al) was applied to the microarray profiling to generate the following TNBCtypes–Basal-Like 1 (BL1), Basal-Like 2 (BL2), Mesenchymal (M), mesenchymal stem–like (MSL), and luminal androgen receptor (LAR). Immunomodulatory +/- (IM) status was assigned independent of the subtypes. Sequencing of BRCA1/2 from tumor DNA was also performed. The subtypes were tested for prognostic effect on DFS and OS using Cox regression model with adjustment for nodal status.

Results: For 425 TNBC patients, the median age was 45 years, 33% were node-positive and 10-year DFS and OS = 66.3% and 74.1%, respectively. A total of 381/424 (89.7%) cases could be classified into TNBCtypes with distribution as follows: BL1=24%, BL2=8%, M=24%, MSL=11%, LAR=9%, unclassified (UNL) =24%. No association between TNBCtypes and race or nodal status was noted. Compared to other subtypes LAR subtype was associated with older age at diagnosis (median age 53 vs 45, p<0.001). Overall 24% of samples were IM+ and 25% demonstrated deleterious tBRCA1/2 mutation. DFS, tBRCA1/2 mutation and IM+ status distribution across different subtypes are provided in the table. All subtypes except for LAR demonstrated a drop in hazard function for recurrence after 5 years.

 5 year DFS (%)10 year DFS (%)DFS HR (95% CI), p valueDeleterious tBRCA1/2 mutationIM+ statusBL184.5%77.5%141%60%BL281.3%70.5%1.59 (0.81-3.13) p = 0.1816%12%M69.2%61.2%2.06 (1.25-3.40) p = 0.00528%0%MSL54.8%50.0%2.38 (1.33-4.28) p = 0.00418%7%LAR74.3%53.8%2.24 (1.22-4.14) p = 0.0112%8%UNL76.4%71.8%1.36 (0.80-2.33) p = 0.2620%30%

Conclusions: In the presence of adjuvant AC, TNBC molecular subtypes have varied prognosis, with BL1 subtype demonstrating the best prognosis and MSL and LAR subtypes demonstrating the worst prognosis. LAR subtype is associated with older age at diagnosis and continued elevated hazard function for recurrence after year 5. tBRCA1/2 mutations are distributed across all subtypes with the highest prevalence in BL1 and M subtypes. IM+ status was infrequently noted in non-BL1 subtypes. These findings underscore TNBC heterogeneity and the need to account for this heterogeneity in prospective clinical trials.

Citation Format: Sharma P, Barlow WB, Hout DR, Seitz RS, Bailey DB, Godwin AK, Pathak H, Timms KM, Solimeno C, Linden HM, Porter P, Tripathy D, Hortobagyi GN, Thompson A, Pusztai L, Hayes DF. Impact of molecular subtypes on long-term outcomes in triple-negative breast cancer (TNBC) patients treated with adjuvant AC chemotherapy on SWOG S9313 [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P4-08-06.

Abstract P2-06-22: PEA15-AA, an unphosphorylatable mutant of PEA15, as a novel therapeutic gene for triple-negative breast cancer

Background: Triple-negative breast cancer (TNBC) is an aggressive subtype of breast cancer characterized by a high rate of metastatic recurrence and poor prognosis. Molecular mechanism underlying the metastatic behavior of TNBC has not been well elucidated, and newer approaches addressing drivers of metastasis are crucial to improving patient outcomes. PEA15 (Phosphoprotein enriched in astrocytes-15) regulates cell proliferation, apoptosis, and autophagy. In breast cancer, PEA15 expression inhibits invasion by binding to ERK and preventing its nuclear translocation. The biological function of PEA15 is tightly regulated by its phosphorylation at Ser104 and Ser116. However, the effect of PEA15 phosphorylation status on TNBC remains unknown. In this study, we tested the hypothesis that unphosphorylated PEA15 will prevent metastasis in TNBC through inhibition of the epithelial-to-mesenchymal transition (EMT).

Method: We established stable cells overexpressing unphosphorylatable (PEA15-AA) and phospho-mimetic (PEA15-DD) PEA15 mutants in MDA-MB-468 cells. To dissect specific Cellular Mechanisms regulated by PEA15 phosphorylation, we performed RT-PCR immune and metastasis arrays. In vivo mouse models were used to see effects of PEA15 phosphorylation on tumor growth.

Results: The clonogenic growth of PEA15-AA–expressing cells was significantly reduced by 80% compared with empty vector-transfected cells (PEA15-V). Anchorage-independent growth, an indicator of in vivo tumorigenicity, was inhibited in cells expressing PEA15-AA by 60% compared with PEA15-V. PEA15-AA upregulated the expression of E-cadherin and decreased the expression of mesenchymal markers, suggesting that PEA15-AA reverses EMT. Compared with PEA15-V, migration and invasion of cells expressing PEA15-AA were reduced by 65% and 72%, respectively. In contrast, PEA15-DD promoted migration, invasion, and expression of mesenchymal markers. To determine the in vivo effect of PEA15-AA, we injected stable PEA15 transfectants of MDA-MB-468 cells into the mammary fat pad of NOD/SCID mice. The PEA15-DD–injected group showed greater tumor volumes than PEA15-V and PEA15-AA groups, suggesting that PEA15-AA has antitumor effects both in vitro and in vivo. From the immune and metastasis arrays, we found that expression level of IL-8, which is known to induce EMT, was greatly decreased by PEA15-AA, while IL-8 was highly expressed in PEA15-DD cells. Addition of recombinant IL-8 to the cells expressing PEA15-AA partially rescued mesenchymal characteristics, increasing migration and expression of mesenchymal markers. By contrast, IL-8 knockdown in PEA15-DD–expressing cells decreased the mesenchymal phenotype. These findings indicate that IL-8 may play an important role as a mediator of phosphorylation of PEA-15 in breast cancer cell migration and invasion and suggest that PEA15-AA inhibits the expression of IL-8, thereby reversing EMT.

Conclusion: Taken together, our results show that PEA15 phosphorylation serves as an important regulator, having a dual role as an oncogene or tumor suppressor. Further studies are warranted to evaluate the impact of PEA15 phosphorylation status on metastasis in vivo. These findings support the development of PEA15-AA as a potential therapeutic strategy for TNBC.

Citation Format: Park J, Chauhan G, Cohen EN, Ueno NT, Battula VL, Tripathy D, Reuben JM, Bartholomeusz C. PEA15-AA, an unphosphorylatable mutant of PEA15, as a novel therapeutic gene for triple-negative breast cancer [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P2-06-22.

Comparative efficacy of adjuvant trastuzumab-containing chemotherapies for patients with early HER2-positive primary breast cancer: a network meta-analysis

BACKGROUND

Trastuzumab (H) with chemotherapy benefits patients with HER2+ breast cancer (BC); however, we lack head-to-head pairwise assessment of survival or cardiotoxicity for specific combinations. We sought to identify optimal combinations.

METHODS

We searched PubMed, updated October 2017, using keywords "Breast Neoplasms/drug therapy," "Trastuzumab," and "Clinical Trial" and searched Cochrane Library. Our search included randomized trials of adjuvant H plus chemotherapy for early-stage HER2+ BC, and excluding trials of neoadjuvant therapy or without data to obtain hazard ratios (HRs) for outcomes. Following PRISMA guidelines, one investigator did initial search; two others independently confirmed and extracted information; and consensus with another investigator resolved disagreements. Before gathering data, we set outcomes of overall survival (OS), event-free survival (EFS), and severe cardiac adverse events (SCAEs). Analyzing 6 trials and 13,621 patients, we made direct and indirect comparisons using network meta-analysis on HR for OS or EFS and on odds ratio (OR) for SCAE; ranked therapy was done based on outcomes using p scores.

RESULTS

Compared with anthracycline-cyclophosphamide with taxane (ACT), ACT with concurrent H (ACT+H) showed best OS (HR 0.63, 95% confidence interval [CI] 0.55, 0.72), followed by taxane and carboplatin (TC) with concurrent H (TC+H) (HR 0.77, 95% CI 0.59, 1) and ACT with sequential H (ACT-H) (HR 0.85, 95% CI 0.68, 1.05). Pairwise comparisons showed statistically significant OS benefit for ACT+H over others; similar results for EFS. TC+H showed statistically significant lower SCAE risk compared to ACT+H (OR 0.13, 95% CI 0.03, 0.61).

CONCLUSIONS

Concurrent H with ACT or TC showed most clinical benefit for early-stage HER2+ BC; TC+H had lowest cardiotoxicity.

Revisiting the definition of estrogen receptor positivity in HER2-negative primary breast cancer

Background

Although 1% has been used as cut-off for estrogen receptor (ER) positivity, several studies have reported that tumors with ER < 1% have characteristics similar to those with 1% ≤ ER < 10%. We hypothesized that in patients with human epidermal growth factor 2 (HER2)-negative breast cancer, a cut-off of 10% is more useful than one of 1% in discriminating for both a better pathological complete response (pCR) rate to neoadjuvant chemotherapy and a better long-term outcome with adjuvant hormonal therapy. Our objectives were to identify a percentage of ER expression below which pCR was likely and to determine whether this cut-off value can identify patients who would benefit from adjuvant hormonal therapy.

Patients and methods

Patients with stage II or III HER2-negative primary breast cancer who received neoadjuvant chemotherapy followed by definitive surgery between June 1982 and June 2013 were included. Logistic regression models were used to assess the association between each variable and pCR. Cox models were used to analyze time to recurrence and overall survival. The recursive partitioning and regression trees method was used to calculate the cut-off value of ER expression.

Results

A total of 3055 patients were analyzed. Low percentage of ER was significantly associated with high pCR rate (OR = 0.99, 95% CI = 0.986-0.994, P < 0.001). The recommended cut-off of ER expression below which pCR was likely was 9.5%. Among patients with ER ≥ 10% tumors, but not those with 1%≤ER < 10% tumors, adjuvant hormonal therapy was significantly associated with long time to recurrence (HR = 0.24, 95% CI = 0.16-0.36, P < 0.001) and overall survival (HR = 0.32, 95% CI = 0.2-0.5, P < 0.001).

Conclusion

Stage II or III HER2-negative primary breast cancer with ER < 10% behaves clinically like triple-negative breast cancer in terms of pCR and survival outcomes and patients with such tumors may have a limited benefit from adjuvant hormonal therapy. It may be more clinically relevant to define triple-negative breast cancer as HER2-negative breast cancer with <10%, rather than <1%, of ER and/or progesterone receptor expression.

Abstract OT3-05-07: PATINA: A randomized open label phase III trial to evaluate the efficacy and safety of palbociclib + anti HER2 therapy + endocrine therapy vs anti HER2 therapy + endocrine therapy after induction treatment for hormone receptor positive, HER2 positive metastatic breast cancer

Background

Pre-clinical data and initial results from clinical studies point to the added benefit of CDK4/6 inhibition when combined with anti-HER2 tx. The current study is designed to evaluate the added benefit of palbociclib when given in combination with anti-HER2 and endocrine tx maintenance in the 1st†line setting of metastatic HER2+HR+ breast cancer.

Trial design

PATINA is an international, open-label, pivotal Phase III study. Primary objective is to demonstrate that the combination of palbociclib with anti-HER2 plus endocrine tx is superior to anti-HER2 plus endocrine tx in prolonging PFS. Sample size is 496 pts. The study starts after completion of 6-8 cycles of chemotherapy-containing anti-HER2 tx for metastatic breast cancer in the 1st line setting. Pts are eligible provided they are without evidence of disease progression by local assessment (i.e. CR, PR or SD). To account for the need for less intense tx regimens for a subset of pts diagnosed with HER2+ER+ disease, clinicians may recommend the combination of trastuzumab with either a taxane or vinorelbine prior to study initiation. Clinicians might also choose a non-pertuzumab option for pts previously treated with pertuzumab in the neo(adjuvant) setting. Secondary objectives include measures of tumor control (OR, CBR, DOR), OS, safety and QOL. The translational science main objective is to compare PFS estimates according to PIK3CA mutation status assessed by cfDNA analysis. Endocrine tx options are AI or fulvestrant. Premenopausal pts must receive ovarian suppression. The study has a 90% power to detect a hazard ratio of 0.667 in favor of the palbociclib arm. Pts approached to participate in AFT-38 will be asked to indicate on the informed consent forms whether remaining biospecimens and clinical data from the control arm of the study can be shared with the Mastering Breast Cancer (MBC) Initiative. The overarching purpose of the MBC is to create a mechanism for understanding the natural history of metastatic breast cancer by cataloguing longitudinally studied tumor-specific markers and treatment effects.

ClinicalTrials.gov Identifier: NCT02947685

Citation Format: Metzger-Filho O, Mandrekar S, Loibl S, Ciruelos E, Gianni L, Lim E, Miller K, Huang C, Koehler M, Francis P, Valagussa P, Goel S, Prat A, Goetz M, Loi S, Krop I, Carey L, Lanzillotti J, Winer E, Tripathy D, DeMichele A. PATINA: A randomized open label phase III trial to evaluate the efficacy and safety of palbociclib + anti HER2 therapy + endocrine therapy vs anti HER2 therapy + endocrine therapy after induction treatment for hormone receptor positive, HER2 positive metastatic breast cancer [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr OT3-05-07.