T-DM1 Therapy Research Articles

Long-term complete remission under TDM1 and local radiotherapy treatment on an inflammatory HER2-positive breast cancer

Premenopausal female patient is diagnosed at the age of 45 for locally advanced inflammatory HER2-positive breast cancer with axillary node involvement. Her disease reveals bad prognostic factors. In spite of radical mastectomy after intensive neoadjuvant treatment based on chemotherapy and trastuzumab-pertuzumab, early skin infiltration recurrence overcomes. She receives local radiotherapy and TDM1 therapy as first advanced disease line. Toxic side effects are not relevant. She achieves four-years-long disease-free survival. Precise treatment selection is challenging but can find out cancer defeat.

Impact of obesity on safety outcomes and treatment modifications with ado-trastuzumab emtansine in breast cancer patients

Ado-trastuzumab emtansine (T-DM1) is an antibody-drug conjugate indicated for the treatment of HER2-positive breast cancer. The 2012 American Society of Clinical Oncology guidelines on chemotherapy dosing in obesity recommend using full weight-based cytotoxic chemotherapy doses to treat obese patients with cancer. These guidelines were published prior to the advent of anticancer antibody-drug conjugates. There is a need to investigate the safety of T-DM1 in obese patients. This retrospective chart review included adult patients with breast cancer receiving T-DM1. The primary endpoint was a composite of the incidence of T-DM1 treatment modifications secondary to an adverse event. Secondary outcomes included the incidence of dose reductions, dose delays, treatment discontinuations, and adverse events. A total of 119 patients with HER2-positive breast cancer who received T-DM1 therapy were included in this study: 44 obese patients and 75 non-obese patients. The composite outcome of treatment modifications due to toxicity was significantly higher in obese patients compared to non-obese patients (45% vs 25%, p = 0.024). Treatment delays were significantly higher in obese patients (36% vs 16%, p = 0.011). All-grade adverse events with a higher incidence in obese patients included left ventricular ejection fraction decrease (11% vs 5%), bilirubin increase (32% vs 12%), thrombocytopenia (61% vs 55%), and peripheral neuropathy (34% vs 27%). This study suggests obese patients receiving T-DM1 may require more treatment modifications secondary to adverse events compared to non-obese patients. Larger studies are needed to determine if obese patients are at higher risk for specific T-DM1-induced adverse events.

Peritoneal dissemination of breast cancer diagnosed by laparoscopy

The accuracy of modern imaging techniques for the diagnosis of peritoneal carcinomatosis is poor. A breast cancer patient with a high serum CA15-3 level did not receive a definitive diagnosis of peritoneal dissemination by imaging examination and then underwent laparoscopy. Pathological examination showed peritoneal dissemination of breast cancer, but the biological markers were different from the primary lesion: ER(−), PgR(−), and Her2:3 +. T-DM1 therapy was very effective, and her systemic symptoms disappeared. Since biomarkers of metastatic lesions may sometimes change, laparoscopic biopsy is very important and useful.

Abstract 5853: Identification of TSC1 and TSC2 as potential determinants of sensitivity to trastuzumab emtansine

Abstract Trastuzumab emtansine (T-DM1, Kadcyla) is an antibody-drug conjugate used in the treatment of HER2-positive breast cancer. However, its use is limited by acquired and intrinsic resistance, the mechanisms of which are not well understood. Further knowledge of T-DM1 resistance may provide new combination strategies or therapeutic targets to overcome resistance or new predictive biomarkers to identify the patients most likely to benefit from T-DM1 therapy. To discover genes responsible for T-DM1 sensitivity and resistance in an unbiased manner, we have conducted CRISPR/Cas9 functional genomics screens by a two-stage process. Firstly, we performed whole genome screens in MDA-MB-361 and MDA-MB-453 cells transduced with Cas9 and the GeCKOv2 lentiviral library that were exposed to T-DM1 and its effector DM1 for 8-13 weeks. Gene knockouts enriched or depleted in response to T-DM1 or DM1 treatment in either cell line were identified by sequencing of genomic DNA and differentially expressed genes by RNA sequencing, revealing 599 candidate genes of T-DM1 sensitivity. For high-throughput validation of the 599 genes, we developed a custom library of 2539 guide RNAs (gRNAs) to target these 599 genes, plus non-targeting controls. Cas9-expressing MDA-MB-361 cells were transduced with the custom library and exposed to T-DM1 for 28 days. MAGeCK analysis of gRNA sequencing revealed 11 genes that were significantly enriched and one gene that was significantly depleted at a false discovery rate (FDR) of <0.1. Two of the top hits in the secondary screen were two genes whose loss is known to promote T-DM1 resistance: ERBB2 (HER2) and SLC46A3 (P<8 × 10−5; FDR <0.007). Other top hits were TSC1 and TSC2 (P<3 × 10−6; FDR= 0.0004); which are both tumor suppressor genes and negative regulators of mTOR complex 1 (mTORC1). For subsequent validation, we have generated TSC2 knockout cell pools, which were more resistant to T-DM1 than wildtype cells in a competition growth assay. Knockout clones have been isolated and are being tested for T-DM1 resistance. Since mTOR inhibitors can phenocopy TSC1 and TSC2 by inhibiting mTORC1 activity, we have also evaluated T-DM1 in combination with the mTOR inhibitor KU-0063794 in a sulforhodamine B assay in MDA-MB-361 and MDA-MB-453 cells. Each agent potently inhibited cell proliferation and demonstrated synergistic anti-proliferative activity in combination. Together, our results suggest that TSC1 and TSC2 knockout may promote T-DM1 resistance and that targeting mTOR may be an effective strategy to overcome T-DM1 resistance. Citation Format: Francis W. Hunter, Barbara A. Lipert, Kyla N. Siemens, Aziza Khan, Hilary R. Barker, Troy W. Ketela, William R. Wilson, Tet-Woo Lee, Stephen M. Jamieson. Identification of TSC1 and TSC2 as potential determinants of sensitivity to trastuzumab emtansine [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 5853.

Abstract 2898: A biparatopic HER2xHER2 antibody drug conjugate with potent anti-tumor activity

Abstract A biparatopic HER2xHER2 antibody drug conjugate with potent anti-tumor activity. The antibody drug conjugate (ADC) Trastuzumab-emtansine (T-DM1) targets the well-characterized breast cancer oncogene HER2 and is active in tumors that express very high levels of HER2 protein. However, tumors expressing intermediate levels of HER2 remain resistant to T-DM1 therapy, apparently due to insufficient lysosomal trafficking of T-DM1. We generated a series of biparatopic HER2xHER2 antibodies in which each arm recognizes a distinct epitope of HER2. One of our HER2xHER2 antibodies bound to cells with greater avidity than Trastuzumab and formed visible cell surface clusters that were efficiently internalized. While some of the internalized HER2xHER2 antibody trafficked to lysosomes and promoted HER2 degradation, a significant fraction recycled back to the plasma membrane through recycling endosomes. To exploit the increased internalization and recycling of the HER2xHER2 antibody, ADCs were generated by site-specific conjugation of Tubulysin A payload through a protease-cleavable linker. Recent data suggest that cleavage of this linker does not require lysosomal trafficking, but can occur in recycling endosomes as well. HER2xHER2-Tubulysin killed cell lines expressing high (IHC3+) and intermediate (IHC2+) HER2 levels with subnanomolar IC50, while exhibiting very weak killing of cells expressing low (IHC1+) HER2 levels (IC50 greater than 10nM). HER2xHER2-Tubulysin induced complete and durable tumor regression and outperformed T-DM1 in a collection of IHC3+ and 2+ tumor xenograft models (including PDX). Our work shows that a detailed understanding of antibody trafficking can enable the design of more effective ADCs and suggests that HER2xHER2-Tubulysin is a potential clinical candidate for HER2 IHC2+ breast cancer. Citation Format: Andres Perez Bay, Devon Faulkner, Shiwani Tiwari, Carla Castanaro, Xiang Zheng, Arthur Kunz, Thomas Nittoli, Amy Han, William Olson, Gavin Thurston, Christopher Daly, Julian Andreev. A biparatopic HER2xHER2 antibody drug conjugate with potent anti-tumor activity [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 2898.

Real-world effectiveness of post-T-DM1 treatments in HER2-positive metastatic breast cancer: KBCSG-TR1917 observational study.

e13020 Background: For patients with HER2-positive, unresectable and/or metastatic breast cancer (HER2+ mBC), T-DM1 is now the standard of care after trastuzumab and/or pertuzumab-based therapy. On the other hand, there is limited evidence after T-DM1 treatment. To clarify the treatment options and the effectiveness of drug therapy just after T-DM1 (post–T-DM1 therapy), we performed a multicenter observational study in patients with HER2+ mBC. Methods: This study enrolled consecutive patients who met eligibility criteria; Japanese female patients with HER2+ mBC, 20 years of age or older, who received at least one subsequent drug treatment except for an investigational drug after discontinuing T-DM1 between Jan 2014 and Dec 2018. To investigate the effectiveness of post–T-DM1 therapy, the real-world progression-free survival (rwPFS), time to treatment failure (TTF), overall survival (OS), objective response rate (ORR) and clinical benefit rate (CBR) were evaluated. Tumor response was exactly assessed by investigators according to RECISTv1.1. Results: Of 205 patients who were treated with T-DM1 at five institutions, 138 patients were enrolled and 128 patients were included in the analysis (data-cut off: Jul 31 2019). The median age of the patients was 59 years (range 27–84), and the median duration of T-DM1 treatment was 5.1 months (range 0.0–41.4). Ninety-two patients (71.9%) had an ECOG PS score of 0 or 1. Of the 128 patients, 34 (26.6%) patients received lapatinib + capecitabine therapy, 35 (27.3%) trastuzumab-based therapy (excluding pertuzumab), 36 (28.1%) pertuzumab-containing therapy, and 23 (18.0%) other therapy except for anti-HER2 therapy. In the 111 patients with measurable lesions, ORR was 22.5% (95% CI: 15.1–31.4). The median rwPFS was 5.7 months (95% CI: 4.8–6.9), median TTF 5.6 months (95% CI: 4.6–6.4), median OS 22.8 months (95% CI: 18.2–32.4), and the CBR was 47.7% (95% CI: 38.8–56.7) in the 128 patients. Conclusions: We clarified that the effectiveness of post–T-DM1 therapy was limited among the current standard treatment options. Therefore, to improve the prognosis in the later settings of HER2+ mBC, novel treatment options are warranted in the future. Clinical trial information: UMIN000038296 .

ARX788, a novel anti-HER2 antibody-drug conjugate, shows anti-tumor effects in preclinical models of trastuzumab emtansine-resistant HER2-positive breast cancer and gastric cancer.

The majority of HER2-positive breast or gastric cancers treated with T-DM1 eventually show resistance to this agent. We compared the effects of T-DM1 and ARX788, a novel anti-HER2 antibody-drug conjugate, on cell growth and apoptosis in HER2-positive breast cancer and gastric cancer cell lines sensitive to T-DM1, gastric cancer cell lines resistant to T-DM1, HER2-negative breast cancer cell lines, and T-DM1-resistant xenograft models. ARX788 was effective in T-DM1-resistant in vitro and in vivo models of HER2-positive breast cancer and gastric cancer. ARX788 showed a pronounced growth inhibitory effect on all five HER2-positive cell lines tested, of which two gastric cancer cell lines had acquired resistance to T-DM1. ARX788 evoked more apoptotic events compared to T-DM1. While JIMT-1 and RN-87 xenograft tumors progressed on T-DM1 treatment, all such tumors responded to ARX788, and four out of the six JIMT-1 tumors and nine out of the twelve RN-87 tumors disappeared during the ARX788 treatment. Mice treated with ARX788 survived longer than those treated with T-DM1. The data support evaluation of ARX788 in patients with HER2-positive breast cancer or gastric cancer including cancers that progress during T-DM1 therapy.

Predicting Thrombocytopenia in Patients With Breast Cancer Treated With Ado-trastuzumab Emtansine

IntroductionThrombocytopenia is a common and potentially serious adverse event of ado-trastuzumab emtansine (T-DM1) use in patients with advanced breast cancer. However, the risk factors have been minimally explored. Our aim was to develop a clinical prediction model from the clinicopathologic data that would allow for quantification of the personalized risks of thrombocytopenia from T-DM1 usage. Materials and MethodsData from 3 clinical trials, EMILIA (a study of trastuzumab emtansine versus capecitabine + lapatinib in participants with HER2 [human epidermal growth factor receptor 2]-positive locally advanced or metastatic breast cancer), TH3RESA (a study of trastuzumab emtansine in comparison with treatment of physician's choice in participants with HER2-positive breast cancer who have received at least two prior regimens of HER2-directed therapy), and MARIANNE [a study of trastuzumab emtansine (T-DM1) plus pertuzumab/pertuzumab placebo versus trastuzumab (Herceptin) plus a taxane in participants with metastatic breast cancer], were pooled. Cox proportional hazard analysis was used to assess the association between the pretreatment clinicopathologic data and grade ≥ 3 thrombocytopenia occurring within the first 365 days of T-DM1 use. A multivariable clinical prediction model was developed using a backward elimination process. ResultsOf the 1620 participants, 141 (9%) had experienced grade ≥ 3 thrombocytopenia. On univariable analysis, the body mass index, race, presence of brain metastasis, platelet count, white blood cell count, and concomitant corticosteroid use were significantly associated with the occurrence of grade ≥ 3 thrombocytopenia (P < .05). The multivariable prediction model was optimally defined by race (Asian vs. non-Asian) and platelet count (100-220 vs. 220-300 vs. >300 × 109/L). A large discrimination between the prognostic subgroups was observed. The highest risk subgroup (Asian and platelet count of 100-220 cells ×109/L) had a 40% probability of grade ≥ 3 thrombocytopenia within the first 365 days of T-DM1 therapy compared with 2% for the lowest risk subgroup (non-Asian and platelet count > 300 × 109/L). ConclusionA clinical prediction model, defined by race and pretreatment platelet count, was able to discriminate subgroups with a significantly different risk of grade ≥ 3 thrombocytopenia after T-DM1 initiation. The model allows for improved interpretation of the personalized risks and risk/benefit ratio of T-DM1.

Abstract A011: Preclinical models of breast cancer brain metastasis for drug efficacy studies

Abstract Background: Overall, 10-30% of patients with metastatic breast cancer (BC) will develop brain metastases. Depending on the subtype of the primary breast cancer the incidence of brain metastases varies ranging from 14% (hormone receptor positive BC) to 46% (triple-negative BC) and approximately about 34% for patients with HER2-positive BC. The major impact of the blood-brain-barrier (BBB), BBB efflux pumps and the local microenvironment in the brain represent a challenge for treatment of BC brain metastasis and treatment options remain limited. The aim of this study was to develop a model system of breast cancer brain metastases for evaluation of drugs directed at BC brain metastases. Methods: Models of BC brain metastasis were established by intracranial stereotactic injection of enzymatically digested PDX tumors (ST340, ST941, ST1339, ST1616B, ST1360B, and ST3338) or by intracardiac or intracarotid injection of cell suspensions in nude mice. Contrast-enhanced T1- and T2-weighted magnetic resonance imaging (MRI) or bioluminescence imaging was used to determine tumor take and growth. Drug sensitivity to single agent trastuzumab emtansine (T-DM1) administered intravenously were performed at confirmed tumor take in a subset of the models. Mice were treated with either saline or T-DM1, 10 mg/kg/week x4 or 2 mg/kg/week x4. PET imaging with 18F-FES was applied in estrogen receptor (ER) positive models as a PD biomarker of anti-estrogen receptor endocrine therapy. Results: T-DM1 treatment in the intracranial ST1339 or ST3338 HER2 positive (3+) PDX models inhibited tumor growth and prolonged survival compared to non-treated animals. However, T-DM1 treatment only caused a modest growth delay in the ST3338 model established intracranially compared to a complete response in the model established subcutaneously. Delivery of T-DM1 across the BBB to the intracranial tumors was visualized by 64Cu-trastuzumab PET/CT and high tumor uptake was associated with a response to T-DM1 therapy in the ST1339 model. Models of BC brain metastasis were successfully established by the intracardiac or intracarotid methods for the triple negative BC cell line MDA-MB-231, the HER2 positive cell line BT474, and an ER positive cell line (ST941C). In vivo imaging with 18F-FES PET/CT was able to visualize intracranial ER positive BC tumors, and animals treated with fulvestrant exhibited reduced 18F-FES tumor uptake. Conclusion: We have established model systems of BC brain metastasis and drug efficacy evaluation. Treatment response to T-DM1 was observed in intracranial HER2 positive models and delivery of T-DM1 to the tumors was visualized by 64Cu-trastuzumab PET/CT imaging. Together, the established breast cancer brain metastases models in combination with advanced non-invasive imaging can be used as a relevant translational platform for evaluation of new drugs. Citation Format: Carsten H. Nielsen, Michael J. Wick, Lotte K. Kristensen, Henriette S. Joergensen, Maria Z. Alfsen, Mark U. Juul, Alyssa Moriarty, Kyriakos P. Papadopoulos, Andreas Kjaer. Preclinical models of breast cancer brain metastasis for drug efficacy studies [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference on Molecular Targets and Cancer Therapeutics; 2019 Oct 26-30; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2019;18(12 Suppl):Abstract nr A011. doi:10.1158/1535-7163.TARG-19-A011

Precision Medicine Tools to Guide Therapy and Monitor Response to Treatment in a HER-2+ Gastric Cancer Patient: Case Report

Trastuzumab, has played a major role in improving treatment outcomes in HER-2 positive gastric cancer. However, once there is disease progression there is a paucity of evidence for second line therapy. Patient-derived xenografts (PDXs) in combination with liquid biopsies can help guide individual therapeutic decisions and have now started to be studied. In the present case we established a PDX model from a metastatic HER-2+ gastric cancer patient and after the first engraftment passage we performed a mouse clinical trial to test T-DM1 as an alternative therapy for the patient. The PDX tumor response served as a guide to administer T-DM1 therapy to the patient who responded to treatment before relapsing 6 months later. Throughout out the clinical follow up of the patient, ctDNA levels of HER-2 copy number and a PIK3CA mutation were monitored and we found their correlation with drug response and disease progression to outperform that of CEA levels. This study highlights the utility of applying precision medicine tools combining PDX models to guide therapy with circulating tumor DNA (ctDNA) to monitor treatment response and disease progression.

Abstract 233: Bispecific HER2 ADC: Making more potent HER2 ADC by improving target internalization

Abstract Trastuzumab-emtansine (T-DM1) targets the well-characterized breast cancer oncogene HER2, and has shown success in the clinic, but tumors expressing intermediate levels of HER2 remain resistant to T-DM1 therapy, apparently due to insufficient lysosomal trafficking of T-DM1. Here, we engineered bispecific HER2-DM1 conjugates that bridge HER2 with the rapidly internalizing receptor APLP2. The high affinity arm of HER2xAPLP2 bispecific antibodies mediates surface binding to HER2+ tumor cells (but not to HER2- normal cells). After binding to HER2, the low affinity APLP2 arm promotes antibody internalization and lysosomal degradation. The strength of the APLP2 arm allows for modulation of the degree of internalization, degradation and killing. In in vitro killing assays, HER2xAPLP2-DM1 were significantly more potent than T-DM1 in cell lines expressing high (IHC3+) and intermediate (IHC 2+) levels of HER2, albeit induced little or no killing in cell lines expressing low HER2 levels (IHC 1+). Monovalent APLP2-ADCs induced little or no killing in all cell lines tested. Selected HER2xAPLP2-DM1 conjugates had acceptable PK profile in APLP2 humanized mice while significantly outperforming T-DM1 in inhibiting growth of IHC2+ tumor xenografts. These data pave the way to generate clinical candidate ADCs that will improve on T-DM1. In addition, our study opens up a possibility to exploit internalizing proteins such as APLP2 in combination with bispecific antibodies to enhance efficacy of ADCs. Citation Format: Andres Perez Bay, Anuj Kalsy, Shiwani Tiwari, Bo Luan, Art Kunz, Zhaoyuan Chen, Li Zhang, Terra Potocky, Thomas Nittoli, Gavin Thurston, Christopher Daly, Julian Andreev. Bispecific HER2 ADC: Making more potent HER2 ADC by improving target internalization [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 233.

Comparison of outcomes in a population-based cohort of women with metastatic breast cancer receiving anti-HER2 therapy with clinical trial outcomes.

1037 Background: Little data exist for comparing cardiac safety and survival outcomes of anti-HER2 therapy with concurrent trastuzumab (T) and pertuzumab (P) or ado-T emtansine (TDM1) in metastatic breast cancer (MBC) patients enrolled in randomized clinical trial (RCT) vs those in the real world. Furthermore, whether older patients have worse outcomes is unknown. Methods: This was a retrospective population-based cohort of all women with MBC treated with concurrent T with P or TDM1 in Ontario (between 2012 and 2017), identified from New Drug Funding Program and linked to Ontario Cancer Registry and other administrative datasets. Outcomes were incident heart failure (HF, defined as hospitalization or emergency room visit for HF) and overall survival (OS). RCT data were obtained from digitizing survival curves as per established methods and compared with cohort OS data using log-rank test. Age based comparison of outcomes was conducted for women ≥ 65 years old vs younger. Results: Our cohort composed of 833 (28% &gt; 64 years old), and 397 (28% &gt; 64 years old) women treated with P and TDM1, respectively, of which 46 and 30 had baseline HF, respectively. 49% and 99.5% of women received T prior to P and TDM1, respectively. Incident HF following P or TDM1 initiation was low (P 26 women, TDM1 8 women; Table). HF events was not more in women ≥ 65 years old compared to women &lt; 65 treated with P (16 vs. 10, p = 0.23). Unadjusted OS was significantly worse than RCT OS (Table; P HR 1.67, 95% CI 1.37-2.03, p &lt; 0.0001; TDM1 HR 2.80, 95% CI 2.27-3.44, p &lt; 0.0001). Older women had worse OS than younger women for P (HR 1.54, 95% CI 1.22-1.96, p = 0.0003), but not for TDM1 (HR 1.08, 95% CI 0.81-1.43, p = 0.62). Conclusions: HF incidence during P or TDM1 therapy in this real world cohort was relatively low. Survival in this cohort was significantly worse compared to RCT, particularly for older women, suggesting importance of evaluating effectiveness in an unselected patient population to facilitate informed decision-making based on real-world risks and survival outcomes.[Table: see text]

Long-term toxicity profile of trastuzumab emtansine (T-DM1): A multicenter real-life study.

e12507 Background: T-DM1 is widely used in HER2 positive metastatic breast cancer (MBC) patients (pts), often for many cycles until progression. However, little is known about its long term toxicity. The aim of this study was to evaluate the safety profile of T-DM1 when delivered for ≥12 cycles. Methods: HER2 positive MBC pts who had received ≥12 cycles of T-DM1 across 18 Italian cancer centers were enrolled from January 2017 to September 2018. The 12 cycles cut-off was chosen based on the EMILIA trial median PFS (9.6 months), to identify a patient population treated with T-DM1 for longer time. Tumor and clinical characteristics were collected. Standard haematological tests, blood chemistries and side effects (nausea, vomiting, diarrhea, stomatitis, asthenia) were recorded cycle by cycle, according CTCAE criteria version 4. Haematological and laboratory toxicities were available for 86 patients, while other toxicities for all 115 patients. Results: Overall, 115 pts were enrolled. Median age was 54.5 (range 29.6–81.9); median time from diagnosis of metastatic disease to first T-DM1 cycle was 32.5 months. T-DM1 was administered as 2nd line and 3rd line of treatment in 45.2% and 27.8% of pts, respectively. Median number of cycles was 18 (range 12-59). Complete response, partial response and stable disease rates were 11.4%, 43% and 45.6%, respectively. Treatment related side effects are shown in table 1. Interestingly, no increased liver toxicity was observed in pts with liver metastases. Analysis of mean CTCAE grade by cycle showed that no relevant incremental toxicity was observed during long term T-DM1 therapy. Conclusions: T-DM1 is safe and well tolerated in these long responding pts. We found no relevant cumulative toxicity. Patients should be treated with T-DM1 as long as their tumor responds, as no safety issues are related to its long term use. [Table: see text]

Abstract P6-18-26: Ado-trastuzumab for the treatment of metastatic HER2-amplified breast cancer patients previously treated with pertuzumab

Abstract BACKGROUND: Ado-trastuzumab (T-DM1) is an antibody-drug conjugate of trastuzumab and a cytotoxic microtubule-inhibitory agent, emtansine. T-DM1 is approved for the treatment of advanced HER2-amplified breast cancer that progressed following trastuzumab-based therapies based on improvement in progression-free survival (PFS) and overall survival (OS) compared to the therapy of physician choice. However, T-DM1 trials were conducted prior to the widespread adoption of docetaxel, trastuzumab, and pertuzumab as standard frontline therapy for advanced HER2-amplified breast cancer. As such, none of the patients enrolled on T-DM1 studies had been exposed to pertuzumab, and the clinical benefit of T-DM1 in patients previously treated with pertuzumab therapy is unknown. METHODS: We completed a retrospective review of patients at our institution over the age of 18 with metastatic HER2-amplified breast cancer treated with pertuzumab prior to T-DM1 between February 2013 and May 2018. Data was collected on patient and tumor characteristics, number and duration of therapies in the metastatic setting, and clinical outcomes. The primary endpoint of this study was PFS in patients given T-DM1 after earlier exposure to pertuzumab. Secondary endpoints included overall response rate (ORR), prolonged duration of T-DM1 therapy (&amp;gt; 6 months), and OS. Adverse events following T-DM1 were collected using CTCAE 4.03, with a focus on cardiac dysfunction and peripheral neuropathy. Patient features and outcomes were summarized with descriptive statistics and time-to-event measures were analyzed using the Kaplan-Meier method and log-rank test. RESULTS: Twenty patients met the inclusion criteria and are included in this study. The patient population consisted of 18 non-Hispanic white and 2 black women, with a median age of 58.5 (range 34-68) years. The number of prior systemic therapies (excluding pertuzumab) ranged from 0-8 with a median of 1 therapy. The duration of T-DM1 therapy (started, on average, 24 months after metastatic diagnosis) ranged from &amp;lt; 1 month to 3.5 years with a median of 6 months. T-DM1 therapy was overall very well tolerated, with all adverse events being grade ≤2. Of note, 2 patients had grade 2 neuropathy, and one patient had grade 1 cardiotoxicity, without any change in left ventricular ejection. Among 18 patients evaluable for response, ORR was 16.7% (95% CI: 3.6% to 41.4%), with 3 patients achieving a partial response. No complete responses were noted. 10/18 (55.6%) patients had prolonged duration of therapy with T-DM1. Median follow-up time after initiation of T-DM1 was 15 months and 6/20 (30%) patients died while under observation. At the time of data cut-off, 10/20 patients had disease progression on T-DM1. Median PFS was 16 months, with a 1-year PFS rate of 54.5% (95% CI: 36.4% to 81.7%). The 1-year OS rate was 75.0% (95% CI: 58.2% to 96.6%). Patients with liver metastases (n=8) had a significantly worse PFS (p=0.003). CONCLUSION: T-DM1 following pertuzumab is well tolerated and shows excellent efficacy in the treatment of HER2-positive metastatic breast cancer. Comparing T-DM1 following pertuzumab to T-DM1 in pertuzumab-naïve patients should be explored in this patient population. Citation Format: Al Rabadi LS, Kaempf A, Lim JY, Saraceni MM, Savin MA, Mitri ZI. Ado-trastuzumab for the treatment of metastatic HER2-amplified breast cancer patients previously treated with pertuzumab [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 P6-18-26.

Abstract P6-17-22: Progression free survival (PFS) and overall survival (OS) of patients treated with trastuzumab emtansine (T-DM1) after previous treatment with pertuzumab in patients with advanced breast cancer (NCT02338167)

Abstract Background Studies leading to the approval of trastuzumab emtansine (T-DM1) have been conducted without pertuzumab as previous therapy. Therefore data about patient characteristics and the efficacy of T-DM1 after a treatment with pertuzumab is scarce. Aim of this study was to analyze a real world patient cohort of advanced breast cancer (aBC) patients, who were treated with T-DM1 after a treatment containing pertuzumab in the metastatic setting with regard to patient characteristics and progression free survival (PFS). Methods The PRAEGNANT metastatic breast cancer registry (NCT02338167) is a prospective registry for metastatic breast cancer patients with focus on molecular biomarkers. Patients of all therapy lines with any kind of treatment are eligible for this registry. Collected data comprises all relevant patient and tumor characteristics, therapies, adverse events, quality of life, patient reported outcomes, response and survival (PFS/OS). Here we report on the patient characteristics and PFS data for HER2 positive patients treated with T-DM1 after a treatment with pertuzumab. Patients had to be included before or at the beginning of the T-DM1 therapy. Results A total of 58 patients could be identified, who were suitable for the analysis. Of those 34 were treated in the second line, 14 in the third line and 10 in the fourth line or higher. Most of the pertuzumab therapies before T-DM1 were conducted in first line (n=46; 79.3%). Median PFS for all patients was 4.8 months (95% CI: 3.0-7.8 months). Median PFS for patients treated in the 3rdline and 4thline or higher was 4.2 months(95%CI: 2.3 - NA) and 4.0 months (95%CI: 1.8-N.A.), respectively. In patients treated 2ndline with T-DM1 PFS was 7.7 months (95%CI: 2.8 – 12.2). Conclusion T-DM1 is effective as 2ndand further line therapy following pretreatment with pertuzumab. Overall PFS was about 5 months with 7.7 months as 2nd-line therapy. The PFS in higher therapy lines might be shorter. As the sample size of this real world cohort was rather low and analyses have to be considered exploratory, this data need to be confirmed in studies with a larger sample size. Citation Format: Schneeweiss A, Lux MP, Hartkopf AD, Volz B, Kolberg H-C, Hadji P, Tesch H, Haeberle L, Ettl J, Lüftner DI, Wallwiener M, Müller V, Beckmann MW, Belleville E, Wimberger P, Hielscher C, Geberth M, Lermann J, Abenhardt W, Kurbacher C, Wuerstlein R, Thomssen C, Untch M, Overkamp F, Huober J, Taran F-A, Janni W, Wallwiener D, Brucker SY, Fasching PA, Fehm TN. Progression free survival (PFS) and overall survival (OS) of patients treated with trastuzumab emtansine (T-DM1) after previous treatment with pertuzumab in patients with advanced breast cancer (NCT02338167) [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 P6-17-22.

Imaging of HER2 with [89Zr]pertuzumab in Response to T-DM1 Therapy.

Background: The success of human epidermal growth factor receptor 2 (HER2)-targeted therapy depends on accurate characterization of HER2 expression, but current methods available have several limitations. This study aims to investigate the feasibility of [89Zr]pertuzumab imaging to monitor early response to Ado-trastuzumab emtansine (T-DM1) therapy in mice bearing xenografts of HER2-positive breast cancer (BCa). Materials and Methods: Pertuzumab was conjugated to DFO-Bz-NCS and labeled with 89Zr. Mice bearing BT-474 tumors were imaged with [89Zr]pertuzumab and [18F]FDG before and after T-DM1 therapy. Results: Pertuzumab was successfully labeled with 89Zr with a specific activity of 0.740 MBq/μg. Overall [18F]FDG images showed poor delineation of tumors. Using [18F]FDG-PET to measure tumor volume, the volume remained unchanged from 107.6 ± 20.7 mm3 before treatment to 89.87 ± 66.55 mm3 after treatment. In contrast, [89Zr]pertuzumab images showed good delineation of HER2-positive tumors, allowing accurate detection of changes in tumor volume (from 243.80 ± 40.91 mm3 before treatment to 78.4 ± 40.43 mm3 after treatment). Conclusion: [89Zr]pertuzumab may be an imaging probe for monitoring the response of HER2-positive BCa patients to T-DM1 therapy.

Abstract 2174: Intracranial PDX models of breast cancer brain metastases and PET imaging for drug efficacy studies

Abstract Background: Overexpression of the human epidermal growth factor receptor 2 (HER2) is an independent risk factor for development of brain metastases. Between 37-55% of patients with HER2-positive metastatic breast cancer develop brain metastases and the incidence is increasing. A reason for the increase of brain metastases is the improved control of systemic disease by novel therapeutics such as ado-trastuzumab emtansine (T-DM1). However, the major impact of the blood-brain-barrier (BBB), BBB efflux pumps and the local microenvironment in the brain represent a challenge for treatment of brain metastases. The aim of this study was to develop a model system of HER2 positive breast cancer brain metastases for evaluation of drugs directed at brain metastases. Methods: Subcutaneous tumors from a panel of HER2-positive PDX breast cancer models designated ST340, ST1339, ST1616B, ST1360B and ST3338 were enzymatically digested and used for intracranial stereotactic injection or intra carotid injection in nude mice. Contrast-enhanced T1- and T2-weighted Magnetic Resonance Imaging (MRI) were used to determine tumor take and growth. Drug sensitivity studies to single agent T-DM1 administered intravenously were performed at confirmed tumor take in a subset of the models. Mice were treated with either saline or T-DM1, 10 mg/kg/week x4 or 2 mg/kg/week x4. Delivery of T-DM1 to the tumor site was evaluated by PET/CT imaging with 64Cu-trastuzumab. Results: Intracranial tumor growth was detected by MR imaging in all models. T-DM1 treatment of animals with intracranial ST1339 or ST3338 tumors inhibited tumor growth and prolonged survival compared to non-treated animals. A variable response within the treatment groups was observed. Delivery of T-DM1 across the BBB to the intracranial tumors was visualized by 64Cu-trastuzumab PET/CT and high tumor uptake was associated with a response to T-DM1 therapy in the ST1339 model. Conclusion: We have established a model system for evaluating drug sensitivity in HER2 positive breast cancer brain metastases. Treatment response to T-DM1 was observed in the models. 64Cu-trastuzumab PET imaging confirmed delivery of trastuzumab to the tumors, and high uptake was associated with an increased response to T-DM1 therapy. Together, the established PDX models of breast cancer and brain metastases can be used as a relevant translational platform in combination with advanced non-invasive imaging for evaluation of new drugs. Citation Format: Carsten H. Nielsen, Michael J. Wick, Mette M. Jensen, Lotte K. Kristensen, Alyssa Moriarty, Melissa Rundle, Kyriakos P. Papadopoulos, Andreas Kjaer. Intracranial PDX models of breast cancer brain metastases and PET imaging for drug efficacy studies [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 2174.

Efficacy and tolerability of trastuzumab emtansine in advanced human epidermal growth factor receptor 2-positive breast cancer.

The management of human epidermal growth factor receptor 2 (HER2)-positive breast cancer has changed dramatically with the introduction and widespread use of HER2-targeted therapies. There is, however, relatively limited real-world information about the effectiveness and safety of trastuzumab emtansine (T-DM1) in Hong Kong Chinese patients. We assessed the efficacy and toxicity profiles among local patients with HER2-positive advanced breast cancer who had received T-DM1 therapy in the second-line setting and beyond. This retrospective study involved five local centres that provide service for over 80% of the breast cancer population in Hong Kong. The study period was from December 2013 to December 2015. Patients were included if they had recurrent or metastatic histologically confirmed HER2+ breast cancer who had progressed after at least one line of anti-HER2 therapy including trastuzumab. Patients were excluded if they received T-DM1 as first-line treatment for recurrent or metastatic HER2+ breast cancer. Patient charts including biochemical and haematological profiles were reviewed for background information, T-DM1 response, and toxicity data. Adverse events were documented during chemotherapy and 28 days after the last dose of medication. Among 37 patients being included in this study, 28 (75.7%) had two or more lines of anti-HER2 agents and 26 (70.3%) had received two or more lines of palliative chemotherapy. Response assessment revealed that three (8.1%) patients had a complete response, eight (21.6%) a partial response, 11 (29.7%) a stable disease, and 12 (32.4%) a progressive disease; three patients could not be assessed. The median duration of response was 17.3 (95% confidence interval, 8.4-24.8) months. The clinical benefit rate (complete response + partial response + stable disease, ≥12 weeks) was 37.8% (95% confidence interval, 22.2%-53.5%). The median progression-free survival was 6.0 (95% confidence interval, 3.3- 9.8) months and the median overall survival had not been reached by the data cut-off date. Grade 3 or 4 toxicities included thrombocytopaenia (13.5%), raised alanine transaminase (8.1%), anaemia (5.4%), and hypokalaemia (2.7%). No patient died as a result of toxicities. In patients with HER2-positive advanced breast cancer who have been heavily pretreated with anti-HER2 agents and cytotoxic chemotherapy, T-DM1 is well tolerated and provided a meaningful progression-free survival of 6 months and an overall survival that has not been reached. Further studies to identify appropriate patient subgroups are warranted.

Abstract A011: HER2-positive PDX model of breast cancer brain metastasis obtained from patient prior to T-DM1 therapy

Abstract Background: Ado-trastuzumab emtansine (T-DM1), a recently approved antibody-drug conjugate (ADC), is approved for treatment of high HER2-expressing (3+), trastuzumab-resistant breast and gastric cancers. While this agent is effective, HER2-positive breast cancer patients have a high risk of brain relapse, seen in up to 37% of patients of whom half die as a result of failure to control the intracranial disease. The aim of this study was to develop a model system that reflects the breast cancer brain metastases seen in patients undergoing T-DM1 therapy. We collected brain metastasis tissue from an HER2-positive breast cancer patient prior to receiving T-DM1 therapy. Methods: The high HER2-expressing (3+) breast cancer brain metastasis model designated ST3338 was established subcutaneously in athymic nude mice using biopsy material from a brain metastasis obtained from a 42-year-old breast cancer patient. The patient was on T-DM1 therapy following sample collection and had received prior treatment with trastuzumab, bevacizumab, and lapatinib. Immunohisotochemistry of both clinical and PDX tissues was applied to assess the estrogen (ER), progesterone (PR), and HER2 receptor levels. Drug sensitivity studies were performed in the ST3338 model established subcutaneously in athymic nude mice to single-agent T-DM1 administered intravenously as a single dose at 10 mg/kg. The ST3338 was also established orthotopically by stereotactic intracranial inoculation of enzymatically digested ST3338 tumor tissue. Tumor development was monitored by T2-weighted MR imaging and the study endpoint was survival by humane endpoints. Results: Immunohistochemistry of PDX tissues was scored as ER (0), PR (0), and HER2 (3+), which corresponded to the clinical brain metastasis sample: ER (0), PR (0), and HER2 (3+). A single dose of T-DM1 at 10 mg/kg showed tumor regression compared with Day 0 (T/C = 0%) in the subcutaneous setting. The ST3338 model was successfully established orthotopically determined by longitudinal T2-weighted MR imaging, and efficacy data of T-DM1 in the orthotopic/intracranial setting are pending. Conclusion: We have established a model system for evaluating drug sensitivity in HER2-positive breast cancer brain metastases. Treatment response to T-DM1 was observed in the subcutaneous setting. With the combination of subcutaneous and intracranial PDX models of breast cancer brain metastases, new drugs can be tested in preclinical models that more closely mimic the microenvironment and the challenges of drug delivery across the blood-brain barrier in breast cancer patients. Citation Format: Carsten H. Nielsen, Michael J. Wick, Lizette Gamez, Camilla S. Knudsen, Mette M. Jense, Melissa Rundle, Kyriakos P. Papadopoulos, Andreas Kjaer. HER2-positive PDX model of breast cancer brain metastasis obtained from patient prior to T-DM1 therapy [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2017 Oct 26-30; Philadelphia, PA. Philadelphia (PA): AACR; Mol Cancer Ther 2018;17(1 Suppl):Abstract nr A011.

Development and responses of brain metastases during treatment with trastuzumab emtansine (T-DM1) for HER2 positive advanced breast cancer: A single institution experience.

Ado-trastuzumab emtansine (T-DM1) is an antibody-drug conjugate that does not cross an intact blood-brain barrier. In the EMILIA trial of T-DM1 vs capecitabine/lapatinib for HER2 positive advanced breast cancer, all patients had baseline brain imaging, and 9/450 (2%) of patients with negative baseline imaging developed new brain disease during T-DM1. We assessed the frequency of brain progression in clinical practice, without routine baseline imaging. We undertook a retrospective study of all patients treated with T-DM1 at the Royal Marsden Hospital from 2011 to 2016. Data collected included baseline characteristics, previous treatment for advanced breast cancer, sites of metastatic disease, duration of T-DM1, sites of progression, and treatment of CNS progression. Fifty-five patients were identified who had received a median of two prior lines of treatment (range 0-5). All were HER2 positive; 45 patients had IHC 3+ tumors and 10 were ISH positive. Patients received a median of 12 cycles of T-DM1 (range 1-34), and six remain on treatment at the time of analysis. Before commencing T-DM1, 16/55 (29%) had known brain metastases (treated with whole brain [9] stereotactic radiotherapy [6] or both [1]). Brain was the first site of progression in 56% (9/16) patients, with a median time to brain progression of 9.9months (95% CI 3.9-12.2). In patients without known baseline brain metastases, 17.9% (7/39) developed new symptomatic brain disease during T-DM1, after a median of 7.5months (95%CI 3.8-9.6). Brain progression was isolated, with control of extra-cranial disease in 4/7 patients. Only one patient was suitable for stereotactic radiotherapy. Median time to extra-cranial progression in all patients was 11.5months (95% CI 9.1-17.7), and median OS in all patients was 17.8months (95% CI 14.2-22). In patients not screened for brain metastases at baseline, the brain was the first site of progression in a significant proportion. Baseline brain imaging may have a role in standard practice for patients commencing T-DM1 therapy.