Efficacy Of Trastuzumab Emtansine Research Articles

Enhancing the Safety and Efficacy of Trastuzumab Emtansine (T-DM1) Through Nano-Delivery System in Breast Cancer Therapy.

Trastuzumab emtansine (T-DM1), an antibody-drug conjugate, revolutionizes breast cancer therapy by specifically delivering DM1 to human epidermal growth factor receptor 2 (HER2) overexpressing tumor cells, effectively inhibiting cell division and proliferation. While T-DM1 demonstrates superior efficacy and tolerability, T-DM1-induced thrombocytopenia remains a significant adverse event leading to treatment discontinuation. To address this issue, the study investigates the feasibility of using poly(lactic-co-glycolic acid) (PLGA)nanoparticles as a delivery vehicle to conjugate T-DM1, aiming to alleviate T-DM1-induced thrombocytopenia. The T-DM1-conjugated PLGA nanoparticles (NPs-T-DM1) reduce binding to megakaryocytes without compromising the targeting ability for HER2. Administration of NPs-T-DM1 not only significantly inhibits tumor growth but also reduces damage to megakaryocytes, inhibits T-DM1-induced thrombocytopenia, and remarkably improves the safety of antibody-conjugated drugs. This work presents a promising strategy to enhance the safety and efficacy of T-DM1 in antitumor therapy, offering significant potential for advancing clinical application in HER2-positive breast cancer patients.

Efficacy of trastuzumab emtansine (T-DM1) and lapatinib after dual HER2 inhibition with trastuzumab and pertuzumab in patient with metastatic breast cancer: Retrospective data from a French multicenter real-life cohort

PurposeTrastuzumab-emtansine (T-DM1), as well as lapatinib plus capecitabine were proven effective in two Phase III studies, following first-line trastuzumab plus a taxane. The introduction of dual HER2 blockade by trastuzumab and pertuzumab as first-line has positioned T-DM1 into second-line, and lapatinib plus capecitabine beyond, without formal evaluation of these strategies. MethodsESME Data Platform (NCT03275311) included individual data from all patients aged ≥18 years, in whom first-line treatment for metastatic breast cancer (MBC) was initiated between January 1, 2008 and December 31, 2016 in one of the 18 French Comprehensive Cancer Centers. The efficacy of T-DM1 and lapatinib plus capecitabine combination, following double blockade associating trastuzumab and pertuzumab were evaluated in this national real-life database. Eligibility criteria were: female, MBC, HER2+ tumor, first-line taxane-based chemotherapy and dual HER2-blockage by trastuzumab plus pertuzumab. Cohort A received second-line T-DM1, and Cohort B second-line T-DM1 and third or fourth-line lapatinib plus capecitabine. ResultsCohort A comprised 233 patients, and Cohort B 47 patients. Median progression-free survival (PFS) was 7.1 months in Cohort A and 4.6 months in Cohort B. Median overall survival were 36.7 months and 12.9 months, respectively. PFS was significantly dependent on the preceding treatment line's duration. In cohort A, HER2 expression status was a significant predictive factor of PFS. ConclusionFirst-line trastuzumab plus pertuzumab do not markedly diminish T-DM1's efficacy in second-line. Similarly, sequential treatment with trastuzumab plus pertuzumab then T-DM1 does not noticeably modify the efficacy of lapatinib plus capecitabine.

Abstract PS4-13: Irreversible inhibition of HER2 activating mutations with neratinib enhances the pre-clinical efficacy of trastuzumab emtansine and trastuzumab deruxtecan

Abstract Background: HER2 activating mutations occur in 2-5% of metastatic breast cancer (MBC) patients, and three phase II or basket clinical trials have shown that the irreversible pan-HER tyrosine kinase inhibitor, neratinib, has good single agent efficacy for HER2 mutated MBC patients. Current trials are combining neratinib with other targeted therapies to increase response rate and progression free survival for these patients. Methods: We established patient derived xenografts (PDX) and organoids from two patients with HER2 mutated, non-amplified MBC and used them to test neratinib with the antibody drug conjugates (ADC’s), trastuzumab emtansine (T-DM1) and trastuzumab deruxtecan (T-DXd), both in 3D culture and in vivo. Real time, in vivo uptake of these ADC’s was visualized with a near infrared fluorophore. Results: PDX lines WHIM51 and WHIM64 were established from ER+, HER2 non-amplified MBC patients that had HER2 activating mutations. WHIM51 has HER2 exon 20 insertion mutation at amino acid 776 (ERBB2 A775_G776insYVMA) and WHIM64 has a HER2 L869R missense mutation, both of which are located in the HER2 tyrosine kinase domain. Both of these HER2 mutations have been previously characterized and are known activating mutations. Organoids were established from both PDX’s and were grown in 3D culture. Drug combination testing of neratinib with T-DM1 in 3D culture showed strong synergy and the mechanism was explored. We demonstrate that neratinib and other irreversible HER2 inhibitors increase the endocytic uptake of T-DM1, but this effect does not occur with the reversible HER2 inhibitors, tucatinib and lapatinib. Real time, in vivo uptake of T-DM1 was measured by labeling the ADC with a near infrared fluorophore and we observed statistically significant increase in T-DM1 uptake with neratinib pre-treatment. Combining neratinib with T-DM1 increased apoptosis at day 3 post-treatment and enhanced tumor shrinkage. With the FDA approval of T-DXd at the end of 2019, we hypothesized that this same mechanism may apply to neratinib combined with T-DXd. We have tested both the combinations of neratinib + T-DXd and neratinib + T-DM1 in vivo in both HER2 mutant PDX’s and observed statistically significant tumor regression with the neratinib + ADC combinations as compared to either T-DXd or T-DM1 on its own. Conclusions: Neratinib increases the endocytosis of trastuzumab emtansine (T-DM1) and trastuzumab deruxtecan (T-DXd), thereby increasing tumor cell kill and causing greater tumor regression in HER2 mutated MBC. These data provide preclinical justification for trials of neratinib plus HER2 ADCs including T-DXd or T-DM1 in HER2 mutant or HER2+ MBC. Further, this mechanism of neratinib stimulated HER2 endocytosis may also apply to HER2 low MBC. Citation Format: Ron Bose, Shunqiang Li, Tina M. Primeau, Maureen K. Highkin, Ashley R. Tipton, Nagalaxmi Vemalapally, Xuefeng Gao, Gail Sudlow, Irmina Diala, Yu Tao, Jingqin Luo, Ian Hagemann, Chieh-Yu Lin, Richard P. Bryce, Alshad S. Lalani, Samuel Achilefu, Cynthia X. Ma. Irreversible inhibition of HER2 activating mutations with neratinib enhances the pre-clinical efficacy of trastuzumab emtansine and trastuzumab deruxtecan [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PS4-13.

Trastuzumab emtansine of the treatment of HER2-positive breast cancer with brain metatases

Patients with brain metastases of HER2-positive breast cancer (BC) is a special group of patients who are difficult to treat and have a short life expectancy. The possibilities of whole brain radiotherapy, stereotactic radiosurgery and surgery in such patients are rather limited. Trastuzumab emtansine (T-DM1) showed potential activity in this subset of patients. T-DM1 is an antibody-chemical conjugate (ADC) that delivers directly to HER2-positive cancer cells, thereby limiting damage to healthy tissue. At this point, the efficacy of trastuzumab emtansine has been demonstrated in several randomized trials as a second and subsequent lines of therapy for advanced breast cancer with a favorable toxicity profile of the drug. This article describes a clinical case of a patient with luminal B HER-2 positive breast cancer who, underwent stereotactic radiosurgery and was treated with trastuzumab emtansine as a the second line of treatment for disease progression with metastatic brain lesions after trastuzumab/pertuzumab-containing therapy. Partial regression of metastases with long-term duration of the effect was achieved treatment with trastuzumab emtazine has been being continued for 24 months. Tolerability of therapy was good: thrombocytopenia 2 degree was the main among side effects. The effect has been persisted for 2 years and the patient continues the treatment. Discussion of the results of real clinical practice with well-known studies was carried out.

Efficacy of trastuzumab emtansine in Japanese patients with previously treated HER2-positive locally advanced or metastatic gastric or gastroesophageal junction adenocarcinoma: A subgroup analysis of the GATSBY study.

The phase II/III GATSBY study (NCT01641939) showed that trastuzumab emtansine did not have an efficacy benefit over taxane in patients with previously treated, human epidermal growth factor receptor 2 (HER2)-positive advanced or metastatic gastric or gastroesophageal junction cancer. We evaluated patients from Japanese centers within GATSBY. In stage one, patients (randomized 2:2:1) received trastuzumab emtansine 3.6mg/kg every 3weeks, trastuzumab emtansine 2.4mg/kg weekly, or physician's choice of taxane (docetaxel 75mg/m² every 3weeks or paclitaxel 80mg/m² weekly). In stage two, patients (randomized 2:1) received trastuzumab emtansine 2.4mg/kg weekly or taxane. Eligible patients had centrally assessed HER2-positive disease and progression during or after first-line therapy. Primary endpoint was overall survival. We present the 2.4mg/kg weekly data. Eighty-two patients were randomized (intention-to-treat: 48 to trastuzumab emtansine 2.4mg/kg weekly, 23 to taxane; September 2012-August 2014) at 19 sites. Median overall survival was 11.8 months (95% confidence interval [CI], 9.3-16.3) with trastuzumab emtansine 2.4mg/kg weekly and 10.0 months (95% CI, 7.1-18.2) with taxane (unstratified hazard ratio=0.94, 95% CI, 0.52-1.72). Trastuzumab emtansine 2.4mg/kg weekly, versus taxane, was associated with fewer grade ≥3 adverse events (AEs; 52.1% vs 68.2%) and serious AEs (14.6% vs 18.2%). There were no fatal AEs. Efficacy in Japanese patients within GATSBY was consistent with the overall population; overall survival was not prolonged with trastuzumab emtansine 2.4mg/kg weekly versus taxane. The safety profile of trastuzumab emtansine was similar to the overall population.

Significance of baseline neutrophil-to-lymphocyte ratio for progression-free survival of patients with HER2-positive breast cancer treated with trastuzumab emtansine

The efficacy of trastuzumab emtansine (T-DM1) is prolonged for some patients; however, the predictive factors remain unknown. We focused on a peripheral blood biomarker, the neutrophil-to-lymphocyte ratio (NLR), regarding T-DM1 treatment efficacy. Fifty-three advanced or metastatic breast cancers treated with T-DM1 were retrospectively recruited from three institutes. The NLR in the peripheral blood was measured at baseline and after one cycle. The cutoff value of the NLR was set at median value 2.56. The progression-free survival (PFS) of patients with NLR-low at baseline (n = 26; median, not reached) was significantly better than that of patients with NLR-high (n = 27; median, 4.13 months; hazard ratio [HR], 0.226; 95% confidence interval [CI], 0.112–0.493; p = 0.0001). Longer overall survival was significantly associated with a low NLR (HR, 0.384; 95% CI, 0.170–0.910; p = 0.0296). In the subgroup analysis, patients with NLR-low consistently had longer PFS compared to those with NLR-high irrespective of the number of prior chemotherapy regimens, prior trastuzumab, visceral metastasis, estrogen receptor status, and human epidermal growth factor receptor 2 (HER2) score. Although detailed mechanisms remain unknown, treatment efficacy of T-DM1 may be partly mediated by activation of the immune system. Low baseline NLR appears to be beneficial for treatment with T-DM1 in HER2-positive breast cancers.

Comparison of the efficacy of trastuzumab emtansine between patients with metastatic human epidermal growth factor receptor 2-positive breast cancers previously treated with combination trastuzumab and pertuzumab and with trastuzumab only in Japanese population

BackgroundTrastuzumab emtansine (T-DM1) has been approved since 2013 for patients with human epidermal growth factor receptor 2 (HER2)-positive metastatic breast cancer (MBC) who had received trastuzumab (Tmab) and taxane. However, no clinical trial has evaluated the efficacy of T-DM1 in those who have previously received pertuzumab (Pmab). This study aimed to compare the efficacy of T-DM1 between patients who had received Tmab and Pmab and those who had received Tmab only in Japanese population.MethodsWe identified all patients with HER2-positive MBC who received T-DM1 between April 1, 2014 and February 28, 2017 in our institution. The patients were divided into the Tmab group (i.e., those who received only Tmab before T-DM1 treatment) and the Tmab/Pmab group (i.e., those who received Tmab and Pmab before T-DM1 treatment), and progression-free survival (PFS) and best response were compared between the two groups.ResultsA total of 42 patients were enrolled for outcome analysis. The median follow-up period was 4.8 months, and the median number of prior chemotherapy regimens for metastatic disease before T-DM1 was 1 (range 1–2) in the Tmab/Pmab group and 2 (range 0–6) in the Tmab group. The median PFS was 2.8 months in the Tmab/Pmab group (95% confidence interval [CI] 1.7–4.8 months) and 7.8 months in the Tmab group (95% CI 5.5–15.9 months) (p = 0.0030). The best response was lower in the Tmab/Pmab group (11.1% vs. 25.0%).ConclusionsPatients with HER2-positive MBC who received Tmab and Pmab treatment before T-DM1 have fewer benefits from T-DM1.

Efficacy of trastuzumab emtansine (T-DM1) in patients (pts) with HER2+ metastatic breast cancer (MBC) previously treated with pertuzumab (P).

1023 Background: T-DM1 was approved for pts with HER2+ MBC previously treated with trastuzumab (H) and a taxane based on the phase III EMILIA study. P in combination with H + docetaxel (T) later became the first-line standard of care for HER2+ MBC, but there are limited data on T-DM1 efficacy in pts who previously received P. We present exploratory efficacy results from pts treated with T-DM1 any time after P from 2 phase III studies: CLEOPATRA and PHEREXA. Methods: CLEOPATRA (NCT00567190) and PHEREXA (NCT01026142) are randomized, 2-arm trials evaluating P-based regimens for HER2+ MBC. CLEOPATRA studies H + T + P vs HT + placebo in pts with no prior anti-HER2 treatment (tx) or chemotherapy for MBC, while PHEREXA studies H + capecitabine (C) +/− P in pts who progressed during/after previous H tx for MBC. We assessed overall survival (OS) in an exploratory analysis of pts who either received or did not receive T-DM1 at any time after discontinuing study-assigned tx in CLEOPATRA or PHEREXA. Results: Of 408 pts who received HTP in CLEOPATRA and 228 pts who received HCP in PHEREXA, 32 and 43 pts received subsequent T-DM1, respectively (Table). Median duration of T-DM1 tx was 7.1 mo (range 0−44) and 4.2 mo (range 0−22), respectively, and median time from discontinuation of P to start of T-DM1 was 3.5 mo (range 1−47) and 10.6 mo (range 1−28). Conclusions: Although data are limited in these exploratory analyses, our results provide additional evidence of T-DM1 clinical activity in pts with HER2+ MBC who progressed on prior P + H, a finding with real-world implications. Clinical trial information: NCT00567190, NCT01026142. [Table: see text]

Abstract P1-12-10: Safety and efficacy of trastuzumab emtansine (T-DM1) in 399 patients with central nervous system metastases: Exploratory subgroup analysis from the KAMILLA study

Abstract Introduction T-DM1 treatment significantly improved overall survival and had a lower incidence of grade ≥3 adverse events (AEs) vs capecitabine plus lapatinib in patients (pts) with HER2-positive advanced breast cancer (BC) in the EMILIA study, including pts with treated, asymptomatic CNS metastases (mets). KAMILLA is an ongoing, single-arm, open-label, phase 3b global safety study of T-DM1 in pts with HER2-positive locally-advanced or metastatic BC (target n=2220). In this interim analysis we describe clinical characteristics, safety, and efficacy in pts with stable CNS mets at baseline (BL). Methods Eligible pts received prior HER2-directed therapy and chemotherapy and progressed on or after most recent treatment for advanced BC, or within 6 months of completing adjuvant therapy. Pts with asymptomatic CNS mets were eligible, including pts with stable CNS disease with prior radiation therapy. Pts received T-DM1 3.6 mg/kg every 3 weeks until unacceptable toxicity, withdrawal of consent, or disease progression. This exploratory analysis describes pts with BL CNS mets. Median progression-free survival (PFS) was estimated using the Kaplan-Meier method. Results As of April 4, 2016, data were available for 2017 treated pts, of whom 399 (20%) had BL CNS mets, with a median follow-up of 33 months. Table 1 presents demographic and BL characteristics. The incidence of AEs was similar between pts with and without BL CNS mets. Serious AEs (SAEs) occurred in 112 pts with BL CNS mets (28%) vs 311 of 1618 pts without BL CNS mets (19%), and the frequency of SAEs was comparable to that observed in EMILIA. However, nervous system disorder SAEs, such as seizure, epilepsy, and brain edema, occurred more frequently in pts with BL CNS mets (30 pts [8%]) vs 18 pts [1%] with no BL CNS mets. Mean T-DM1 treatment duration was 8.0 months (median 8 cycles; range 1–55) in pts with BL CNS mets and 9.4 months (median 9 cycles; range 1–57) in pts with no BL CNS mets. Median PFS was 5.5 months in pts with BL CNS mets vs 7.9 months in pts with no BL CNS mets. A decrease in the size of brain target lesions was observed during T-DM1 treatment in 84 of 126 pts with measurable CNS lesions. Table 1. BL characteristics CNS mets at BL (n=399)No BL CNS mets (n=1618)Median age, yrs (range)52 (28–83)55 (26–88)ECOG performance status, n (%) 0193 (48)929 (57)1174 (44)605 (37)232 (8)83 (5)Hormone receptor status, n (%) ER and/or PR positive246 (62)992 (61)ER and PR negative149 (37)593 (37)Median time since initial BC diagnosis, yrs (range)4.8 (0–28)5.0 (0–53)Median time since first metastasis, yrs (range)2.4 (0–25)2.6 (0–35)Median number of prior therapies for metastatic BC (range)3 (0–>10)2 (0–>10) Conclusions This subgroup analysis of KAMILLA is the largest reported cohort of pts with CNS mets treated with T-DM1. The overall safety profile of T-DM1 in pts with BL CNS mets was comparable to that of pts without CNS mets. As might be expected in pts with CNS disease, serious neurological AEs occurred more frequently in pts with BL CNS mets vs those without. Response to T-DM1 was seen in the CNS in pts with BL CNS mets, however, median PFS was lower in pts with BL CNS mets vs those without BL CNS mets. Citation Format: Montemurro F, Ellis P, Delaloge S, Wuerstlein R, Anton A, Button P, Lindegger N, Barrios C. Safety and efficacy of trastuzumab emtansine (T-DM1) in 399 patients with central nervous system metastases: Exploratory subgroup analysis from the KAMILLA study [abstract]. In: Proceedings of the 2016 San Antonio Breast Cancer Symposium; 2016 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2017;77(4 Suppl):Abstract nr P1-12-10.

Abstract 5187: PET imaging of trastuzumab emtansine (T-DM1) drug delivery to intracranial patient derived xenograft (PDX) models of breast cancer metastasis

Abstract Background: It is estimated that 10-30% of all breast cancer patients at some point develop brain metastases. Overexpression of the human epidermal growth factor receptor 2 (HER2) is a independent risk factor for development of brain metastases. Up to 37% of patients with HER2-positive metastatic breast cancer develop brain metastases and half of these patients die as a result of failure to control the intracranial disease. A reason for this is the challenge to obtain efficient drug delivery across the blood brain barrier (BBB). Subcutaneous patient derived xenograft (PDX) models are increasingly used for efficacy studies in drug development. However, when targeting brain tumors or metastases, the major impact of the BBB on drug bioavailability must be taken into consideration. Clinical PET imaging with 64Cu or 89Zr labeled trastuzumab has previously been able to visualize breast cancer brain metastases. The aim of our study was to investigate if PET imaging with 64Cu-labeled trastuzumab was predictive of the efficacy of trastuzumab emtansine (T-DM1) in a HER2 positive breast cancer PDX model established as an intracranial brain metastases model. Methods: The intracranial PDX model was established by stereotactic intracranial injection of enzymatically digested ST1339 tumor tissue. At confirmed tumor take, mice were randomized into two arms: control and T-DM1 (10 mg/kg/week x4). Treatment response was monitored by contrast-enhanced T1- and T2-weighted Magnetic Resonance Imaging (MRI) and positron emission tomography (PET) with the amino acid radiotracer O-(2-18F-fluoroethyl)-L-tyrosine (18F-FET). PET/CT imaging with 64Cu-trastuzumab was performed in animals with confirmed intracranial ST1339 tumors prior to treatment with T-DM1 (10 mg/kg/week x4). Results: T-DM1 treatment with 10 mg/kg/week x4 of mice with intracranial tumors inhibited tumor growth and prolonged survival compared to non-treated animals. A variable response within the treatment group was observed. Forty percent had tumor shrinkage while 60% exhibited tumor growth within the duration of the therapy. The intracranial tumors were clearly visible on the 64Cu-trastuzumab PET images co-registered with T2-weighted MR images for anatomical localization. Interestingly, the intracranial tumor uptake between the animals was rather heterogeneous. Conclusion: A treatment response to T-DM1 was observed in an intracranial ST1339 HER2 positive breast cancer PDX model. PET imaging with 64Cu-trastuzumab confirmed delivery of trastuzumab to the tumors. Further quantitative image analysis of the intracranial 64Cu-trastuzumab tumor uptake will reveal if the drug delivery measured by 64Cu-trastuzumab PET imaging is predictive of the efficacy of T-DM1 in a HER2 positive PDX breast cancer brain metastases model. Citation Format: Carsten Haagen Nielsen, Mette K. Nedergaard, Lotte K. Kristensen, Camilla S. Knudsen, Michael J. Wick, Kyri Papadopoulos, Anthony Tolcher, Andreas Kjaer. PET imaging of trastuzumab emtansine (T-DM1) drug delivery to intracranial patient derived xenograft (PDX) models of breast cancer metastasis. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 5187.

Safety and Efficacy of Trastuzumab Emtansine in Advanced Human Epidermal Growth Factor Receptor 2-Positive Breast Cancer: a Meta-analysis.

Advanced or metastatic breast cancer is an incurable disease with high mortality rate worldwide and about 20% of breast cancers overexpress and amplify the human epidermal growth factor receptor 2 (HER2). Achievements in targeted therapy have benefited people during the past decades. Trastuzumab emtansine (T-DM1), a novel antibody-drug conjugate playing a powerful role in anti-tumor activity, not only blocks the HER2 signaling pathways, but also disturbs the microtubule dynamics. To access the efficacy and safety of T-DM1, we analyzed 9 clinical trials on T-DM1. Results showed that fatigue (0.604, 95% CI 0.551, 0.654), nausea (0.450, 95% CI 0.365, 0.537), increased transaminases (0.425, 95% CI 0.353, 0.500) and thrombocytopenia (0.383, 95% CI 0.322, 0.448) occurred more frequently in participants with single T-DM1. In controlled trials, increased transaminases (OR = 4.040, 95% CI 1.429, 11.427), thrombocytopenia (OR = 8.500, 95% CI 3.964, 18.226) and fatigue (OR = 1.288, 95% CI 1.041, 1.593) were statistically significant. Only thrombocytopenia appeared as severe adverse event (grade ≥ 3) in single-arm and control-arm studies. Meanwhile, T-DM1 stabilized cancer and prolonged life with notable improved progression-free survival (PFS) and overall survival (OS). In conclusion, it is a safe and effective agent in advanced or metastatic breast cancer, but should be carefully applied on patients with severe hepatic and neurological disease.

Abstract A15: Efficacy of trastuzumab emtansine (T-DM1) in subcutaneous and intracranial patient derived xenograft models of breast cancer metastasis

Abstract Background: It is estimated that 10-30% of all breast cancer patients at some point develop brain metastases. Overexpression of the human epidermal growth factor receptor 2 (HER2) is a independent risk factor for development of brain metastases. Up to 37% of patients with HER2-positive metastatic breast cancer develop brain metastases and half of these patients die as a result of failure to control the intracranial disease. A reason for this is the challenge of efficient drug delivery across the blood brain barrier (BBB). Subcutaneous patient derived xenograft (PDX) models are increasingly used for efficacy studies in drug development. However, when targeting brain tumors or metastases, the major impact of the BBB on drug bioavailability must be taken into consideration. The aim of this study was therefore to compare the efficacy of trastuzumab emtansine (T-DM1) in a HER2 positive breast cancer PDX model established subcutaneously and as an intracranial brain metastases model. Methods: Mice were implanted subcutaneously with the HER2 positive breast cancer PDX model designated ST1339 and randomized into 3 treatment arms: Control, T-DM1 (5 mg/kg/week x4) and T-DM1 (10 mg/kg/week x4). Treatment response of subcutaneous tumors was monitored by caliper measurements. The intracranial PDX model was established by stereotactic intracranial injection of enzymatically digested ST1339 tumor tissue. At confirmed tumor take, mice were randomized into two arms: Control and T-DM1 (10 mg/kg/week x4). Treatment response was monitored by contrast-enhanced T1- and T2-weighted Magnetic Resonance Imaging (MRI) and positron emission tomography (PET) with the amino acid radiotracer O-(2-18F-fluoroethyl)-L-tyrosine (18F-FET). Results: T-DM1 at 10 mg/kg/week x4 effectively inhibited tumor growth in the subcutaneous model whereas treatment with 5 mg/kg/week x4 did not have any effect on tumor growth. T-DM1 treatment at 10 mg/kg/week x4 of mice with intracranial tumors inhibited tumor growth and prolonged survival compared to non-treated animals. Conclusion: A treatment response to T-DM1 was observed in both the subcutaneous and intracranial ST1339 HER2 positive breast cancer PDX model. With the combination of subcutaneous and intracranial PDX models of breast cancer and breast cancer brain metastases new drugs can thus be tested in preclinical models that more closely mimic the microenvironment and the challenges of drug delivery across the BBB in patients. Citation Format: Carsten H. Nielsen, Mette K. Nedergaard, Lotte K. Kristensen, Camilla S. Knudsen, Michael J. Wick, Kyri Papadopoulos, Anthony W. Tolcher, Andreas Kjaer. Efficacy of trastuzumab emtansine (T-DM1) in subcutaneous and intracranial patient derived xenograft models of breast cancer metastasis. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2015 Nov 5-9; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2015;14(12 Suppl 2):Abstract nr A15.