6-month Clinical Benefit Rate Research Articles

Abstract PO2-27-03: Clinical Results of Subjects Remaining in the Phase 3 ARTEST Study Enobosarm Therapy in AR+ER+HER2- Metastatic Breast Cancer with 3 or Greater Prior Lines of Therapy

Abstract Background: Targeting the androgen receptor (AR) with an oral selective AR agonist, enobosarm, is a novel approach to overcome ER and CDK4/6 inhibitor resistance to suppress AR+ER+HER2- metastatic breast cancer (mBC). Preclinical studies in CDK4/6 inhibitor and estrogen blocking agent resistant PDX mBC models demonstrated that enobosarm alone suppressed tumor growth. In a small subgroup analysis of patients with ER+HER2- mBC who progressed on estrogen blocking agent and a CDK 4/6 inhibitor from the Phase 2 802 study, enobosarm treatment resulted in a best overall response rate of 30% (2 CRs and 1 PR) and a 6-month clinical benefit rate (CBR) of 50%. Methods: The clinical activity of enobosarm 9mg alone was evaluated compared to standard of care (SOC) in the Phase 3 ARTEST, open-label, randomized, multicenter study in AR+ER+HER2-mBC who have progressed on 2 or greater lines of prior therapies, including estrogen blocking agents and CDK4/6 inhibitors. The study was discontinued for administrative reasons not related to efficacy or safety. Results: At the time study was discontinued, 34 patients with confirmed AR positivity were randomized to either enobosarm (n=16) or SOC control (n=18). SOC control treatment group received an average of 2.6 (range 1-5) and enobosarm 9mg monotherapy an average of 2.9 (range 1-5) prior lines of treatment. On average, enobosarm or the SOC control was given in the 4th line treatment for AR+ER+HER2- metastatic breast cancer. In the evaluable population, two partial responses were observed in the enobosarm treatment arm versus no responses in the SOC control arm. In patients with ≤3 lines of prior endocrine therapy, the best objective response rate (ORR) was 18.8% for enobosarm and 0% for control. In patients with ≤3 lines of prior endocrine therapy with ≤1 prior treatment with CDK 4/6 inhibitor, best ORR was 33% in the enobosarm group versus no responses in the SOC control (Table 1). CBR on day 180 was 33.3% (4/12) in the enobosarm group vs 0% (0/11) in the control group. Enobosarm treatment was well tolerated without masculinizing adverse events and no increases in hematocrit changes. Conclusions: Activity of enobosarm in this heavily pretreated patient population is encouraging and supports further clinical investigation. The Phase 3 ENABLAR-2 study is underway to further evaluate enobosarm alone or in combination with abemaciclib for the second-line treatment of AR+ER+HER2- metastatic breast cancer in patients who have received a prior estrogen blocking agent and a CDK 4/6 inhibitor. Clinical trial information: NCT04869943. Research Sponsor: Veru Inc. Table 1. Responses in patients with enobosarm versus SOC treatment. Citation Format: Kristine Rinn, Elisa Krill Jackson, Gary Barnette, Domingo Rodriguez, Itay Shalev, Mitchell Steiner, Joyce O'Shaughnessy, Hope Rugo, Adam Brufsky. Clinical Results of Subjects Remaining in the Phase 3 ARTEST Study Enobosarm Therapy in AR+ER+HER2- Metastatic Breast Cancer with 3 or Greater Prior Lines of Therapy [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO2-27-03.

Clinical outcomes of leuprolide acetate in the treatment of recurrent ovarian granulosa cell tumors

The optimal treatment of recurrent ovarian granulosa cell tumors is not known. Pre-clinical studies and small case series have suggested direct anti-tumor activity of gonadotropin-releasing hormone agonists in the treatment of this disease, but little is known about the efficacy and safety of this approach. To describe patterns of use and clinical outcomes of leuprolide acetate in a cohort of patients with recurrent granulosa cell tumors. This was a retrospective cohort study of patients enrolled in the Rare Gynecologic Malignancy Registry at a large cancer referral center and affiliated county hospital. Patients meeting inclusion criteria had a diagnosis of recurrent granulosa cell tumor and received either leuprolide acetate or traditional chemotherapy as cancer treatment. Outcomes were separately examined for leuprolide acetate used as adjuvant treatment, maintenance therapy, and the treatment of gross disease. Demographic and clinical data were summarized using descriptive statistics. Progression-free survival was calculated from the initiation of treatment to the date of disease progression or death, and compared between groups with the log-rank test. The 6-month clinical benefit rate was defined as the percentage of patients without disease progression 6 months after starting therapy. Sixty-two patients received a total of 78 leuprolide acetate-containing therapy courses, owing to 16 instances of retreatment. Of these 78 courses, 57 (73%) were for treatment of gross disease, 10 (13%) were adjuvant to tumor reductive surgery, and 11 (14%) were for maintenance therapy. Patients had received a median of two (IQR, 1-3) systemic therapy regimens prior to their first leuprolide acetate treatment. Tumor reductive surgery (100% [62/62]) and platinum-based chemotherapy (81% [50/62]) were common prior to first leuprolide acetate exposure. The median duration of leuprolide acetate therapy was 9.6 months (IQR, 4.8-16.5 months). Nearly half of the therapy courses were single-agent leuprolide acetate (49% [38/78]). Combination regimens most often included an aromatase inhibitor (23% [18/78]). Disease progression was the most common cause of discontinuation (77% [60/78]); only one patient (1%) discontinued leuprolide acetate because of adverse events. In the treatment of gross disease, the 6-month clinical benefit rate for first use of leuprolide acetate was 66% (95% CI, 54-82%). Median progression-free survival was not statistically different compared to that which followed chemotherapy (10.3 months [95% CI, 8.0-16.0 months] vs. 8.0 months [95% CI, 5.0-15.3 months], p=0.3). In a large cohort of patients with recurrent granulosa cell tumors, the 6-month clinical benefit rate of first-time leuprolide acetate treatment of gross disease was 66% and progression-free survival was comparable to patients treated with chemotherapy. Leuprolide acetate regimens were heterogeneous, but significant toxicity was rare. These results support leuprolide acetate as safe and effective for the treatment of relapsed adult granulosa cell tumors in the second line and beyond.

Abstract OT2-01-11: ctDNA-guided Adaptive Therapy Escalation in ER+ MBC: A Phase 1b Study with Letrozole, Palbociclib and Onapristone ER

Abstract ctDNA-guided Adaptive Therapy Escalation in ER+ MBC: A Phase 1b Study with Letrozole, Palbociclib and Onapristone ER Background: Extended release onapristone (onapristone ER) is a progesterone receptor (PR) antagonist that inhibits hormone-mediated PR activation and stabilizes PR association with corepressors, resulting in an antineoplastic effect when applied alone or in combination with antiestrogen therapy to breast cancer cells in vitro. Recent preclinical studies further suggest that onapristone adds to inhibition of cell proliferation when combined with CDK4/6 inhibitors and fulvestrant. Elevations in ctDNA can precede overt disease progression by a matter of months in metastatic breast cancer and may represent an opportunity for proactive therapeutic intervention. Trial Design: This is an investigator initiated open-label, single institution phase 1b study of onapristone ER added as escalation therapy in patients with ER+, PR+, HER2 negative MBC, who have detectable ctDNA after six months of treatment with letrozole and palbociclib in the first line. The study is supported by Context Therapeutics and involves two stages. Stage 1 is a dose escalation/de-escalation phase of 18 patients maximum, in which the safety and recommended phase 2 dose (RP2D) will be established for onapristone ER when used in combination with letrozole and palbociclib. In stage 2, the dose expansion phase, the RP2D of onapristone will be combined with letrozole and palbociclib in 10 patients to further explore the tolerability of the regimen. ctDNA will be collected serially while patients are on this triplet therapy. Eligibility Criteria: This study is enrolling patients with radiologically measurable or evaluable metastatic or unresectable ER+/PR+/HER2-negative MBC in whom a tumor-derived somatic mutation can be detected in ctDNA at a variant allele fraction of 0.5% or greater after 6 months (+/- 4 weeks) of treatment with first line letrozole and palbociclib without progression, using our in house CLIA certified MSK-ACCESS assay. Adequate organ function and functional status for enrollment are stipulated in the protocol. Specific Aims: The primary objective of this study is to define the safety, tolerability, and recommended phase 2 dose of onapristone ER used in combination with letrozole and palbociclib. Secondary objectives include to investigate ctDNA response rate of the triplet therapy regimen, to gather early data regarding the 6-month clinical benefit rate, overall response rate, and progression free survival of this triplet escalation therapy regimen in high risk ctDNA+ patients, and to evaluate the pharmacokinetics of Onapristone ER when used in combination with letrozole and Palbociclib. Exploratory objective include to describe ctDNA dynamics during antiprogestin therapy escalation in ER+ MBC, as well as the molecular features present in responders vs. non-responders using ctDNA and pre-treatment tissue. Target Accrual: The total planned cohort for the phase I dose escalation is a maximum of 18 patients across 3 dose levels, and the total planned cohort for the dose expansion is 10 patients, with an anticipated maximum total of 28 patients. We will allot for 5 additional patients to account for inevaluability during the dose escalation and expansion portions of the trial. The trial is currently open to enrollment at MSKCC. Contact Information: Dragoj@mskcc.org; Jhaverik@mskcc.org Citation Format: Joshua Drago, Elaine Walsh, Mithat Gonen, Michael Berger, Mark E. Robson, Sarat Chandarlapaty, Pedram Razavi, Komal Jhaveri. ctDNA-guided Adaptive Therapy Escalation in ER+ MBC: A Phase 1b Study with Letrozole, Palbociclib and Onapristone ER [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr OT2-01-11.

Alpelisib Efficacy in Hormone Receptor-Positive HER2-Negative PIK3CA-Mutant Advanced Breast Cancer Post-Everolimus Treatment.

This real-world cohort analysis assessed the efficacy of alpelisib and endocrine treatment (ET) combinations in a post-everolimus setting. Thirteen women who started alpelisib and ET at standard doses between 2018 and 2022 for advanced breast cancer (ABC), after undergoing CDK4/6i and everolimus treatment, were eligible for the study entry. The primary endpoint was progression-free survival (PFS), and the secondary endpoints were the objective response rate (ORR) and clinical benefit rate (CBR), with different molecular profiling. The patients had previously received a median of four (range 3–8) systemic treatments, including CDK4/6i and everolimus. The median PFS on alpelisib was 5.5 months (range 0.5–10), and four women each had an ORR and three (23%) had a stable disease. The 6-month CBR was 46.1%, similar to the BYLeive study cohort C (47.8%). Notably, our cohort included patients with a long CBR under everolimus treatment (median 6 months, range 1–18); however, the responses to alpelisib and everolimus were not correlated (Pearson r = −0.23, p = 0.44). The PIK3CA, P53, ARID, GATA3, and ESR1 mutations were not associated with the 6-month CBR. Despite heavy pre-treatments, including everolimus, alpelisib was clinically relevant in our cohort, even among patients with an ESR1 mutation. The best treatment sequence for PIK3CA/mTOR inhibitors warrants examination in future trials on PIK3CA-mutant inpatients with luminal ABC.

Abstract OT2-04-01: Circulating tumor DNA-guided adaptive therapy escalation in ER+ MBC: A phase 1b study with letrozole, palbociclib and onapristone ER

Abstract Background: Extended release onapristone (onapristone ER) is a progesterone receptor (PR) antagonist that inhibits hormone-mediated PR activation and stabilizes PR association with corepressors, resulting in an antineoplastic effect when applied alone or in combination with antiestrogen therapy to breast cancer cells in vitro. Recent preclinical studies further suggest that onapristone adds to inhibition of cell proliferation when combined with CDK4/6 inhibitors and fulvestrant. Elevations in ctDNA can precede overt disease progression by a matter of months in metastatic breast cancer and may represent an opportunity for proactive therapeutic intervention. Trial Design: This is an investigator initiated open-label, single institution phase 1b study of onapristone ER added as escalation therapy in patients with ER+, PR+, HER2 negative MBC, who have detectable ctDNA after six months of treatment with letrozole and palbociclib in the first line. The study is supported by Context Therapeutics and will involve two stages. Stage 1 is a dose escalation/de-escalation phase of 18 patients maximum, in which the safety and recommended phase 2 dose (RP2D) will be established for onapristone ER when used in combination with letrozole and palbociclib. In stage 2, the dose expansion phase, the RP2D of onapristone will be combined with letrozole and palbociclib in 10 patients to further explore the tolerability of the regimen. ctDNA will be collected serially while patients are on this triplet therapy. Eligibility Criteria: This study will enroll patients with radiologically measurable or evaluable metastatic or unresectable ER+/PR+/HER2-negative MBC in whom a tumor-derived somatic mutation can be detected in ctDNA at a variant allele fraction of 0.5% or greater after 6 months (+/- 4 weeks) of treatment with first line letrozole and palbociclib without progression, using our in house CLIA certified MSK-ACCESS assay. Adequate organ function and functional status for enrollment are stipulated in the protocol. Specific Aims: The primary objective of this study is to define the safety, tolerability, and recommended phase 2 dose of onapristone ER used in combination with letrozole and palbociclib. Secondary objectives include to investigate ctDNA response rate of the triplet therapy regimen, to gather early data regarding the 6-month clinical benefit rate , overall response rate , and progression free survival of this triplet escalation therapy regimen in high risk ctDNA+ patients, and to evaluate the pharmacokinetics of Onapristone ER when used in combination with letrozole and Palbociclib. Exploratory objective include to describe ctDNA dynamics during antiprogestin therapy escalation in ER+ MBC, as well as the molecular features present in responders vs. non-responders using ctDNA and pre-treatment tissue. Target Accrual: The total planned cohort for the phase I dose escalation is a maximum of 18 patients across 3 dose levels, and the total planned cohort for the dose expansion is 10 patients, with an anticipated maximum total of 28 patients. We will allot for 5 additional patients to account for inevaluability during the dose escalation and expansion portions of the trial. The trial will be open to enrollment at MSKCC in July 2021. Citation Format: Joshua Z Drago, Elaine M Walsh, Mithat Gonen, Michael F Berger, Mark E Robson, Sarat Chandarlapaty, Pedram Razavi, Komal Jhaveri. Circulating tumor DNA-guided adaptive therapy escalation in ER+ MBC: A phase 1b study with letrozole, palbociclib and onapristone ER [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr OT2-04-01.

Abstract P2-13-34: A phase II trial of lapatinib and everolimus for HER2 positive metastatic breast cancer

Abstract Background: Targeted agents against HER2 have been a cornerstone of the treatment armamentarium for HER2 positive breast cancer since the approval of trastuzumab by the FDA in 1998 for metastatic HER2 positive breast cancer. However, many patients will develop resistance to HER2 targeted therapies and succumb to their disease. Novel therapeutic combinations are needed to overcome resistance to currently available therapies and improve patient outcomes. Activation of the mTOR pathway via pTEN loss or PI3K mutation has been identified in vitro as a mechanism of trastuzumab resistance, and preclinical studies have shown that mTOR inhibition enhances the efficacy of trastuzumab by reversing trastuzumab resistance mediated by PTEN loss. Moreover, two phase I trials evaluating the addition of the mTOR inhibitor everolimus to trastuzumab and chemotherapy reversed trastuzumab resistance in patients with heavily pretreated metastatic HER2 positive breast cancer, providing rationale for continued exploration of this combination in phase II trials.Methods: We report the results of a single arm, open-label phase II pilot study for patients with histologically or cytologically confirmed HER2 positive locally advanced or metastatic breast adenocarcinoma that had progressed on at least one prior HER2 targeted therapy. Enrolled patients received everolimus 5 mg PO daily and lapatinib 1000 mg PO daily until disease progression or unacceptable toxicity. Radiographic tumor assessment was performed at trial entry and every 8 weeks thereafter. Primary endpoint was 6-month overall response rate (ORR). Secondary endpoints included 6-month progression free survival (PFS), 6-month clinical benefit rate (CBR), and safety and tolerability of the combination. NCI CTCAE version 4.0 was used for toxicity and serious event reporting. The primary endpoint of 6-month ORR was computed using the point estimate and the 1-sided 97.5% confidence interval by the exact binomial method and compared to the previously reported 7% response rate of lapatinib monotherapy in this setting.Results: A total of 23 patients were enrolled. The median age at enrollment was 48, and the median number of prior lines of therapy was 4 (range 1-9). 13 patients had previously been treated with lapatinib, and CNS disease on trial entry was present in 7 (30.4%) patients. 6-month ORR was 0% (0-14.8%, 97.5% 1-sided CI) and 6-month CBR was 13% (2.8 - 33.6%, 95% CI). Median progression free survival was 112 days (109-115 days, 95% CI). 6-month PFS rate was 13% (2.8-33.6%, 95% CI). No CNS responses were observed. 17 serious adverse events (SAE) of grade 3 or greater were reported. The most common grade 3 or greater SAEs were dyspnea (4 patients - 17%), pleural effusion (3 patients - 13%), abdominal pain and ileal obstruction (2 patients each - 8.7%).Conclusion: The combination of lapatinib and everolimus was not found to be an active regimen in patients who had previously progressed on at least one line of prior HER2 targeted therapy. We would not recommend further exploration of this combination in phase II or phase III trials in this patient population. Citation Format: Anthony Rooney, Priyanka Sharma, Anne P O'Dea, Lauren Nye, Manana Elia, Jianghua He, Carol Fabian, Qamar Khan. A phase II trial of lapatinib and everolimus for HER2 positive metastatic breast cancer [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P2-13-34.

Abstract P1-18-03: Pertuzumab (P) plus high-dose trastuzumab (H) for the treatment of central nervous system (CNS) progression after radiotherapy (RT) in patients (pts) with HER2-positive metastatic breast cancer (MBC): Primary efficacy analysis results from the phase II PATRICIA study

Abstract Background: There is an unmet need for evidence-based systemic therapies for pts with HER2-positive MBC and progressive brain metastases. Despite assumptions that monoclonal antibodies do not cross the blood-brain barrier, molecular imaging in pts shows localization of 89Zr-trastuzumab to brain metastases. Furthermore, preclinical data support dose-dependent activity of H in intracranial tumor models. The PATRICIA study (NCT02536339) evaluated safety and efficacy of P plus high-dose H in pts with HER2-positive MBC with CNS metastases and CNS progression after RT. Herein, we present results from the primary efficacy analysis of PATRICIA. Methods: PATRICIA was a US-based, phase II, open-label, single arm study. Eligible pts had measurable (≥10 mm) CNS disease that had progressed after CNS-directed RT, in the setting of stable extracranial disease. CNS-directed RT included whole-brain RT (WBRT) or stereotactic radiosurgery (SRS) and must have been completed ≥60 days before study entry. Pts received P (840 mg loading dose, then 420 mg every 3 weeks) and high-dose H (6 mg/kg weekly), which continued until progression (CNS or systemic) or unacceptable toxicity. Pts could continue their existing systemic anti-cancer therapy during the study, with the exception of trastuzumab emtansine (T-DM1) or lapatinib. Switch of other anti-cancer therapy was not permitted during the study. Restaging evaluations including brain MRI were completed every 2 cycles. The primary efficacy endpoint was confirmed objective response rate (ORR) in the CNS per Response Assessment in Neuro-Oncology Brain Metastases (RANO-BM) criteria. Secondary endpoints included duration of response (DOR), clinical benefit rate (CBR) in the CNS, and safety. Samples were collected for exploratory pharmacokinetic analyses on Day 1 of weeks 1, 4, 10, and 16. Results: From 15 Dec 2015 to 18 May 2017, 40 pts were enrolled across 16 sites. Median age was 48 (range 34–69) years, with 33% and 67% of pts having an Eastern Cooperative Oncology Group Performance Status score of 0 or 1, respectively. 41% of pts had received prior WBRT only, 28% had received prior SRS only, and 31% had received both. At the data cut off (1 May 2019), of 39 treated pts, 2 remained on study treatment and 37 discontinued treatment, most commonly due to CNS progression (n=27). Median treatment duration was 4.5 (range 0.3–37.3) months. Four pts in the efficacy population (N=37) experienced a confirmed partial response (Table), leading to an ORR of 11% (95% confidence interval [CI], 3–25%). Response durations were 3.2, 3.3, 4.6, and 5.6 months (median DOR 4.6 months). The CBR (complete response + partial response + stable disease [SD] of ≥4 or ≥6 months) was 68% (SD ≥4 months) and 51% (SD ≥6 months). Results from exploratory pharmacokinetic analyses confirmed greater H exposure with the high-dose schedule. The adverse event profile was similar to that previously reported for P and H, with no new safety signals. One pt discontinued treatment due to an adverse event (grade 3 left ventricular dysfunction, considered related to study treatment). No Grade 5 adverse events were reported. Conclusions: The CNS ORR of 11%, ≥6-month CBR of 51%, and lack of any new safety signals suggest that P plus high-dose H may have clinical utility in some pts with HER2-positive MBC with progressive CNS metastases. Table. Efficacy within the CNS per RANO-BM criteriaEfficacy population (N=37)n (%)95% CIORR*4 (11)3, 25CBR (CR + PR + stable disease [SD] ≥4 months)25 (68)50, 82CBR (CR + PR + SD ≥6 months)19 (51)34, 68Confirmed best response (SD ≥4 months)CR0—PR4 (11)—SD ≥4 months21 (57)—Pts without clinical benefit12 (32)—Confirmed best response (SD ≥6 months)CR0—PR4 (11)—SD ≥6 months15 (41)—Pts without clinical benefit18 (49)—*Confirmed complete response (CR) or confirmed partial response (PR). Citation Format: Nancy U Lin, Priya Kumthekar, Solmaz Sahebjam, Nuhad Ibrahim, Anita Fung, Anna Cheng, Alan Nicholas, Bei Wang, Mark Pegram. Pertuzumab (P) plus high-dose trastuzumab (H) for the treatment of central nervous system (CNS) progression after radiotherapy (RT) in patients (pts) with HER2-positive metastatic breast cancer (MBC): Primary efficacy analysis results from the phase II PATRICIA study [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P1-18-03.

TAKTIC: A prospective, multicenter, uncontrolled, phase IB/II study of LY2780301 (LY) in combination with weekly paclitaxel (wP) in HER2-negative locally advanced (LA) or metastatic breast cancer (MBC) patients.

1091 Background: Phosphatidylinositol-3-kinase (PI3K)/AKT/mammalian target of rapamycin (mTOR)-pathway is frequently activated in HER2-negative breast cancer and may play a role in taxane-resistance. LY is a dual inhibitor of p70 S6 kinase and AKT. TAKTIC study aimed to determine the recommended phase II dose (RP2D) of the combination of LY with wP (phase Ib) and to estimate overall response rate (ORR) of this regimen (phase II) in HER2-negative LA or MBC patients, both in the overall patient population and in patients with activation of PI3K/AKT pathway (PI3KAKT+). Methods: HER2-negative inoperable LA or MBC patients (pts), with (phase Ib) or without (phase II) previous cytotoxic treatment for advanced disease were eligible. Oral LY (400 or 500mg) was administered daily in combination with intravenous wP (70 or 80mg/m2). A modified CRM using an adaptive Bayesian model guided the dose escalation of both agents. PI3KAKT+ was defined as activating mutation of PIK3CA and/or AKT by targeted NGS or homozygous loss of PTEN by array comparative genomic hybridization (aCGH) or loss of PTEN by immunohistochemistry, as evaluated on available fresh tumor tissue. Results: A total of 12 and 35 patients (pts) were included in the phase Ib and II, respectively. In phase Ib, only 1 dose-limiting toxicity (confusion) was observed at the last dose level (LY, 500 + wP, 80), which was determined as RP2D. Main drug-related adverse events (AE) in phase Ib were skin toxicity (92% of pts, G3-4 in 33%), and paresthesia (50% of pts, G3-4 in 8%). In the phase II study, ORR was 62.9 % [44.9,78.5] including 1 CR and 21 PR in the overall population and 55.6 % [30.8,78.5] in PI3KAKT+ pts (10 PR in 18 pts). Median progression-free survival was 12.4 months [7.9,17.9] and 6-month clinical benefit rate was 82.9% [66.4,93.4]. AEs in phase II were similar to phase I part, except that 17% of pts experienced pneumonia (G3-4 in 9%). Conclusions: Combining LY and wP in HER2-negative LA or MBC was feasible with preliminary evidences of efficacy, independently of PI3K/AKT activation. Clinical trial information: NCT01980277.

A phase II clinical trial of the Aurora and angiogenic kinase inhibitor ENMD-2076 for previously treated, advanced, or metastatic triple-negative breast cancer

BackgroundTriple-negative breast cancer (TNBC) remains an aggressive breast cancer subtype with limited treatment options. ENMD-2076 is a small-molecule inhibitor of Aurora and angiogenic kinases with proapoptotic and antiproliferative activity in preclinical models of TNBC.MethodsThis dual-institution, single-arm, two-stage, phase II clinical trial enrolled patients with locally advanced or metastatic TNBC previously treated with one to three prior lines of chemotherapy in the advanced setting. Patients were treated with ENMD-2076 250 mg orally once daily with continuous dosing in 4-week cycles until disease progression or unacceptable toxicity occurred. The primary endpoint was 6-month clinical benefit rate (CBR), and secondary endpoints included progression-free survival, pharmacokinetic profile, safety, and biologic correlates in archival and fresh serial tumor biopsies in a subset of patients.ResultsForty-one patients were enrolled. The 6-month CBR was 16.7% (95% CI, 6–32.8%) and included two partial responses. The 4-month CBR was 27.8% (95% CI, 14–45.2%), and the average duration of benefit was 6.5 cycles. Common adverse events included hypertension, fatigue, diarrhea, and nausea. Treatment with ENMD-2076 resulted in a decrease in cellular proliferation and microvessel density and an increase in p53 and p73 expression, consistent with preclinical observations.ConclusionsSingle-agent ENMD-2076 treatment resulted in partial response or clinical benefit lasting more than 6 months in 16.7% of patients with pretreated, advanced, or metastatic TNBC. These results support the development of predictive biomarkers using archival and fresh tumor tissue, as well as consideration of mechanism-based combination strategies.Trial registrationClinicalTrials.gov, NCT01639248. Registered on July 12, 2012.

Abstract PD3-16: Clinical safety and efficacy of the aurora and angiogenic kinase inhibitor ENMD-2076 in previously treated, locally advanced or metastatic triple-negative breast cancer

Abstract Background: Triple-negative breast cancer (TNBC) is an aggressive breast cancer subtype defined by the lack of expression of the estrogen and progesterone receptors and lack of HER2 over-expression. ENMD-2076 is an orally bioavailable small molecule inhibitor of Aurora and angiogenic kinases with pro-apoptotic and antiproliferative activity in preclinical models of TNBC. Methods: This two institution, single-arm, two-stage, phase II clinical trial enrolled patients with locally advanced or metastatic TNBC refractory to 1-3 prior lines of chemotherapy in the advanced setting. Patients had ECOG PS ≤ 1, measureable disease by RECIST 1.1 and no evidence of brain metastasis. Patients were treated with ENMD-2076 250 mg PO daily with continuous dosing in 4-week cycles until disease progression or unacceptable toxicity occurred. The primary end point was 6-month clinical benefit rate (6-CBR) and secondary endpoints included time to progression (TTP), PK profile, safety and biologic correlatives in archival and fresh serial tumor biopsies in a subset of patients. Results: Between July 2012 and October 2016, 41 patients were enrolled (median age 54; range 30-73; female 40; male 1). Patients received a mean 1.7 prior lines of chemotherapy for locally advanced unresectable or metastatic disease and 80.5% received prior neoadjuvant or adjuvant chemotherapy (N=33). Thirty-six patients were evaluable per protocol for the primary efficacy analysis. Five patients (12.2%) were not included in the efficacy analysis due to: adverse events (AE) leading to discontinuation prior to objective efficacy assessment (N=3), not meeting eligibility criteria on day 1 (N=1) and withdraw of consent in cycle 1 (N=1). The study proceeded to the second stage of enrollment based on observing three 6-CBR events in Stage 1 (N=18 patients). The 6-CBR in the overall trial was 16.7% (95% exact CI: 6%-32.8%; 2 patients with PR and 4 patients with SD > 6 mos). The median duration of response or clinical benefit in these patients was 32 weeks (8 cycles). 4-CBR was 27.8% (95% exact CI: 14%-45.2%). Dose reduction occurred in 8 patients (20%) for fatigue, hypertension and proteinuria. The most common grade 3 treatment-related adverse events were hypertension (37.5%) and fatigue (10%). One patient experienced grade 4 hypertension. Analysis of serial tumor biopsies prior to and following 2 weeks of ENMD-2076 (N=8 patients), demonstrated a treatment-induced decrease in cellular proliferation (Ki-67) and microvessel density (CD34) as assessed by IHC. Immunofluorescence performed on a subset of samples demonstrated an increase in p53-family member expression following treatment, consistent with changes observed in preclinical TNBC patient-derived tumor xenograft models. Conclusions: ENMD-2076 has durable clinical activity in a subset of patients with pretreated, advanced or metastatic triple-negative breast cancer. Predictive biomarker development using archival and fresh tumor tissue is underway. Exploration of lower doses of ENMD-2076 in future clinical trials may improve tolerability. Citation Format: Diamond JR, Eckhardt SG, Pitts TM, van Bokhoven A, Aisner D, Gustafson DL, Capasso A, Elias AD, Storniolo AM, Schneider BP, Gao D, Tentler JJ, Borges VF, Miller KD. Clinical safety and efficacy of the aurora and angiogenic kinase inhibitor ENMD-2076 in previously treated, locally advanced or metastatic triple-negative 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 PD3-16.

Phase I trial to evaluate the addition of alisertib to fulvestrant in women with endocrine-resistant, ER+ metastatic breast cancer

PurposeIn estrogen receptor-positive (ER+) breast cancer models, activation of Aurora A kinase (AURKA) is associated with downregulation of ERα expression and resistance to endocrine therapy. Alisertib is an oral selective inhibitor of AURKA. The primary objectives of this phase I trial were to determine the recommended phase II dose (RP2D) and evaluate the toxicities and clinical activity of alisertib combined with fulvestrant in patients with ER+ metastatic breast cancer (MBC).MethodsIn this standard 3 + 3 dose-escalation phase I study, postmenopausal patients with endocrine-resistant, ER+ MBC previously treated with endocrine therapy were assigned to one of two dose levels of alisertib (40 or 50 mg) in combination with fixed-dose fulvestrant.ResultsTen patients enrolled, of which nine were evaluable for the primary endpoint. The median patient age was 59. All patients had secondary (acquired) endocrine resistance, and all had received prior aromatase inhibitor. Six had experienced disease progression on fulvestrant. There were no severe (grade 3+) toxicities reported during cycle 1 at either dose level. The median progression-free survival time was 12.4 months (95% CI 5.3–not met), and the 6-month clinical benefit rate was 77.8% (95% CI 40.0–87.2%).ConclusionsIn patients with endocrine-resistant, ER+ MBC, alisertib in combination with fulvestrant was well tolerated. A favorable safety profile was observed. The RP2D is 50 mg twice daily on days 1–3, 8–10, and 15–17 of a 28-day cycle with standard dose fulvestrant. Promising antitumor activity was observed, including activity among patients with prior progression on fulvestrant.

A phase II trial of abiraterone acetate plus prednisone in patients with triple-negative androgen receptor positive locally advanced or metastatic breast cancer (UCBG 12-1)

Several expression array studies identified molecular apocrine breast cancer (BC) as a subtype that expresses androgen receptor (AR) but not estrogen receptor α. We carried out a multicentre single-arm phase II trial in women with AR-positive, estrogen, progesterone receptor and HER2-negative (triple-negative) metastatic or inoperable locally advanced BC to assess the efficacy and safety of abiraterone acetate (AA) plus prednisone. Patients with a metastatic or locally advanced, centrally reviewed, triple-negative and AR-positive (≥10% by immunohistochemistry, IHC) BC were eligible. Any number of previous lines of chemotherapy was allowed. AA (1000 mg) was administered once a day with prednisone (5 mg) twice a day until disease progression or intolerance. The primary end point was clinical benefit rate (CBR) at 6 months defined as the proportion of patients presenting a complete response (CR), partial response (PR) or stable disease (SD) ≥6 months. Secondary end points were objective response rate (ORR), progression-free survival (PFS) and safety. One hundred and forty-six patients from 27 centres consented for IHC central review. Of the 138 patients with sufficient tissue available, 53 (37.6%) were AR-positive and triple-negative, and 34 of them were included from July 2013 to December 2014. Thirty patients were eligible and evaluable for the primary end point. The 6-month CBR was 20.0% [95% confidence interval (CI) 7.7%-38.6%], including 1 CR and 5 SD ≥6 months, 5 of them still being under treatment at the time of analysis (6.4+, 9.2+, 14.5+, 17.6+, 23.4+ months). The ORR was 6.7% (95% CI 0.8%-22.1%). The median PFS was 2.8 months (95% CI 1.7%-5.4%). Fatigue, hypertension, hypokalaemia and nausea were the most common drug-related adverse events; the majority of them being grade 1 or 2. AA plus prednisone treatment is beneficial for some patients with molecular apocrine tumours and five patients are still on treatment. NCT01842321.

Abstract P6-13-04: A phase I trial to evaluate the safety of the addition of alisertib to fulvestrant in hormone receptor positive (HR+), advanced breast cancer

Abstract Background: During tumor progression, activation of Aurora A kinase (AURKA) is associated with epithelial to mesenchymal transition (EMT) reprogramming and expansion of a subpopulation of tumor initiating cells harboring a CD44+/CD24low/- phenotype [D'Assoro, Oncogene 2014]. These cells are characterized by their capacity to self-renew, resist drug therapies, and promote distant metastases. In ER+ breast cancer (BC) models, activation of AURKA is associated with down-regulation of ERα expression and resistance to endocrine therapy. Alisertib, a selective inhibitor of AURKA, can reverse EMT and restore tumor ERα expression and sensitivity to endocrine therapy [Opyrchal, PLoS One 2014]. As a single agent in HR+ advanced BC, alisertib was associated with a 6-month clinical benefit rate of 54% and median PFS of 7.9 months [Melichar, Lancet Oncol 2015]. The objectives of this phase I trial were to determine the maximum-tolerated dose (MTD) and evaluate the toxicities and clinical activity of alisertib with fulvestrant in patients (pts) with HR+ advanced BC. Methods: In this standard 3+3 dose-escalation phase I study, pts were assigned to two different oral doses of alisertib (40-50 mg BID on days 1-3, 8-10, 15-17 q 28-day cycle) in combination with standard dose fulvestrant (500 mg IM on day 1 and 15 of cycle 1 and then day 1 q 28-day cycle thereafter). Eligibility included HR+ advanced BC, postmenopausal status, measurable disease or nonmeasurable bone disease by RECIST v1.1, ECOG performance status ≤ 1, unlimited prior endocrine therapies, and ≤ 2 chemotherapy regimens in the metastatic setting. Results: Ten pts enrolled September 2014 - April 2015, and 9 were evaluable for the primary endpoint (one excluded due to ineligibility). The median pt age was 59 (range 48, 73). Prior endocrine therapies included AI (9, 100%), fulvestrant (6, 67%), and everolimus/exemestane (5, 56%). Eight pts (89%) had prior chemotherapy. A median of 4 cycles of therapy have been administered (range 1+, 9+). There were no severe (grade 3+) toxicities reported during cycle 1 at either dose level, thus the MTD was not reached. The cycle 1 grade 1/2 adverse events regardless of attribution were fatigue (6, 67%), neutropenia (5, 56%), anemia (5, 56%), leukopenia (4, 44%), diarrhea (3, 33%), nausea (3, 33%), and mucositis (1, 11%). As of June 3, 2015, 2 pts have discontinued treatment due to disease progression, and 7 remain on treatment with stable disease (Table). One pt with bone only disease had a near CR on PET scan. Dose LevelAlisertib Dose (BID)Treatment Cycles≥ Grade 3 Toxicity, All CyclesProgression-Free Survival (days)1 (n=3)40 mg4, 7+, 9+ 117, 170+, 223+2 (n=6)50 mg1+, 2, 3+, 3+, 4+, 5+grade 4 neutropenia (1 pt)28+, 56, 56+, 57+, 112+, 116++ indicates patients still receiving treatment Conclusion: Alisertib in combination with fulvestrant was well-tolerated. The recommended phase II dose is 50 mg twice daily on days 1-3, 8-10, and 15-17 q 28-day cycle with standard dose fulvestrant. Promising antitumor activity was observed. Correlative tissue evaluation of AURKA expression and other EMT biomarkers is underway. Funding: This work was funded by Takeda Oncology and supported by NIH Grant K12 CA90628 [TCH]. Citation Format: Haddad TC, D'Assoro AB, Suman VJ, Opyrchal M, Goetz MP, Ingle JN. A phase I trial to evaluate the safety of the addition of alisertib to fulvestrant in hormone receptor positive (HR+), advanced breast cancer. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr P6-13-04.

Phase I trials in patients with relapsed, advanced upper gastrointestinal carcinomas: experience in a specialist unit

Conventional therapeutic options for patients with advanced upper gastrointestinal cancers (UGIC) are limited. Following first-line treatments, some patients are offered experimental therapies, including participation in Phase I trials. This study aims to describe the experience of UGIC patients treated in a dedicated Phase I unit. Patient, tumour and treatment characteristics, and clinical outcomes of UGIC patients treated consecutively at the Drug Development Unit, Royal Marsden Hospital, between 2005 and 2009, were recorded. Ninety-six patients who previously received a median of 2 (range 1-4) lines of chemotherapies were treated in 30 Phase I trials. Of 81 evaluable patients, 9 achieved RECIST-objective response (11 %) with a 6-month clinical benefit rate of 14 %. Median progression free and overall survival were 7.7 weeks [95 %CI 7.7 (6.4-9.0)] and 19.1 weeks (95 %CI 17.5-20.8), respectively. Grade 3 or 4 toxicities were observed in 37 patients (39 %) and led to trial discontinuation in 9 (9 %); no toxicity-related death was recorded. In the multivariate analysis, serum albumin (<35 g/dl, HR2.0, p = 0.002) and lactate dehydrogenase (>192 μmol/l, HR1.7, p = 0.016) were prognostic of overall survival. Phase I clinical trials can be considered a reasonable option in selected patients with relapsed UGIC. The use of objective prognosticators may improve selection and risk/benefit profile of patients.

GDC-0449 in patients with advanced chondrosarcomas: a French Sarcoma Group/US and French National Cancer Institute Single-Arm Phase II Collaborative Study

BackgroundPre-clinical data have suggested a therapeutic role of Hedgehog (Hh) pathway inhibitors in chondrosarcoma. MethodsThis phase II trial included patients with progressive advanced chondrosarcoma. They received GDC-0449 150 mg/day (days 1–28, 28-day cycle). The primary end point was the 6-month clinical benefit rate (CBR) defined as the proportion of patients with non-progressive disease at 6 months. A 6-month CBR of 40% was considered as a reasonable objective to claim drug efficacy. ResultsBetween February 2011 and February 2012, 45 patients were included. Twenty had received prior chemotherapy. Thirty-nine were assessable for efficacy. The 6-month CBR was 25.6% (95% confidence interval 13.0–42.1). All stable patients had grade 1 or 2 conventional chondrosarcoma with documented progression within the 6 months before inclusion. All but one with available data also had overexpression of the Hh ligand. Median progression-free and overall survivals were 3.5 and 12.4 months, respectively. The most frequent adverse events were grade 1 or 2 myalgia, dysgeusia and alopecia. ConclusionsGDC-0449 did not meet the primary end point of this trial. Results suggest some activity in a subset of patients with progressive grade 1 or 2 conventional chondrosarcoma. Further studies assessing its role in combination with chemotherapy are warranted. ClinicalTrials.gov IdentifierNCT01267955.

Phase II Trial of Bicalutamide in Patients with Androgen Receptor–Positive, Estrogen Receptor–Negative Metastatic Breast Cancer

Patients with hormone receptor-negative breast cancer generally do not benefit from endocrine-targeted therapies. However, a subset with androgen receptor (AR) expression is predicted to respond to antiandrogen therapies. This phase II study explored bicalutamide in AR-positive, estrogen receptor (ER), and progesterone receptor (PgR)-negative metastatic breast cancer. Tumors from patients with ER/PgR-negative advanced breast cancer were tested centrally for AR [immunohistochemistry (IHC) > 10% nuclear staining considered positive]. If either the primary or a metastatic site was positive, patients were eligible to receive the AR antagonist bicalutamide at a dose of 150 mg daily. Clinical benefit rate (CBR), the primary endpoint, was defined as the total number of patients who show a complete response (CR), partial response (PR), or stable disease (SD) > 6 months; secondary endpoints included progression-free survival (PFS) and toxicity. Correlative studies included measurement of circulating endocrine markers and IHC surrogates for basal-like breast cancer. Of 424 patients with ER/PgR-negative breast cancer, 12% tested AR-positive. The 6-month CBR was 19% [95% confidence interval (CI), 7%-39%] for bicalutamide. The median PFS was 12 weeks (95% CI, 11-22 weeks). Bicalutamide was well-tolerated with no grade 4/5 treatment-related adverse events observed. AR was expressed in 12% of patients with ER/PgR-negative breast cancer screened for this trial. The CBR of 19% observed with bicalutamide shows proof of principle for the efficacy of minimally toxic androgen blockade in a select group of patients with ER/PgR-negative, AR-positive breast cancer.

A phase 1 study of weekly dosing of trastuzumab emtansine (T‐DM1) in patients with advanced human epidermal growth factor 2–positive breast cancer

We conducted a phase 1, multicenter, open-label, dose-escalation study (TDM3569g) to assess the safety, tolerability, and pharmacokinetics of single-agent trastuzumab emtansine (T-DM1) administered weekly and once every 3 weeks in patients with HER2-positive metastatic breast cancer previously treated with trastuzumab. The weekly dose results are described here. Patients were administered escalating doses of T-DM1 weekly, starting at 1.2 mg/kg. Additional patients were enrolled at the maximum tolerated dose (MTD) to better characterize tolerability and pharmacokinetics. Twenty-eight patients received weekly T-DM1, and the MTD was determined to be 2.4 mg/kg. In general, T-DM1 was well tolerated, requiring few dose modifications or discontinuations because of adverse events (AEs). Grade ≥ 3 AEs were reported in 19 patients (67.9%); treatment-related AEs occurred in 25 (89.3%) patients. Exposure to weekly T-DM1 was dose-proportional at ≥ 1.2 mg/kg, and accumulation of T-DM1 and total trastuzumab was observed. Objective partial tumor responses were reported in 13 (46.4%) patients; the median duration of response was 18.6 months, and the 6-month clinical benefit rate was 57.1%. The results suggest that a weekly dose of T-DM1 2.4 mg/kg has antitumor activity and is well tolerated in patients with HER2-positive metastatic breast cancer.

Phase II trial of robotic stereotactic radiosurgery (SBRT) in patients with recurrent gynecologic malignancies.

5102 Background: Ablative radiation dose delivered by a robotic SBRT platform has shown progression-free survival benefit in two limited case series among patients with recurrent gynecological malignancies. The therapeutic impact of SBRT on disease progression (PD) was evaluated in the recurrent setting in this phase II trial. Methods: Fifty patients with recurrent and measurable gynecologic malignancy were treated with SBRT. The cohort included patients with recurrent ovarian (n =25), endometrial (n =14), cervical (n =9), or vulvar (n =2) cancer, 1 prior chemotherapy or radiation regimen, and GOG performance status 0, 1, 2. Patients underwent image-guided SBRT in 3 daily doses of 800 cGy = 2400 cGy. SBRT planning target volumes were determined by both the radiation and gynecologic oncologist using non-contrasted CT and 18F-FDG PET/CT overlays. The primary endpoints were 6-month clinical benefit rate (# complete response + # partial response + # stable disease without PD [by RECIST v1.0] / 50), and less than 30-day posttherapy toxicity. Results: Between July 2009 and September 2011, 50 patients were enrolled and have a median posttherapy follow-up of 9 months. At 3 months, 50% (n=25) had complete response, 46% (n=23) had partial response, and 4% (n=2) had stable disease in SBRT-targeted lesions. Twenty-six patients (52%) have had non-SBRT target PD and 18 (36%) have died of PD. Of the 50 patients, 33 had a PD-free interval of at least 6 months, for an overall clinical benefit rate of 66%. Less than 30-day posttherapy SBRT-related toxicities were grade 2 fatigue (n =9 [18%]), grade 2 nausea (n =3[6%], grade 3 nephropathy (n =2[4%]), and grade 4 hyperbilirubinemia (n =1[2%]). Conclusions: This is the first phase II clinical trial of SBRT showing a clinically relevant benefit of ablative radiation in the setting of recurrent gynecological disease. Despite excellent control of targeted lesions with minimal toxicity, non-SBRT target PD rates are high, spurring interest for future SBRT-chemotherapy clinical trials.

Randomized Phase II Trial of Everolimus in Combination With Tamoxifen in Patients With Hormone Receptor–Positive, Human Epidermal Growth Factor Receptor 2–Negative Metastatic Breast Cancer With Prior Exposure to Aromatase Inhibitors: A GINECO Study

Cross-talk between signal transduction pathways likely contributes to hormone resistance in metastatic breast cancer (mBC). Everolimus, an oral inhibitor of the mammalian target of rapamycin, has restored sensitivity in endocrine-resistance models and shown anticancer activity in early-phase mBC clinical trials. This analysis evaluated efficacy and safety of everolimus in combination with tamoxifen in patients with mBC resistant to aromatase inhibitors (AIs). This open-label, phase II study randomly assigned postmenopausal women with hormone receptor-positive, human epidermal growth factor receptor 2-negative, AI-resistant mBC to tamoxifen 20 mg/d plus everolimus 10 mg/d (n = 54) or tamoxifen 20 mg/d alone (n = 57). Randomization was stratified by primary and secondary hormone resistance. Primary end point was clinical benefit rate (CBR), defined as the percentage of all patients with a complete or partial response or stable disease at 6 months. No formal statistical comparison between groups was planned. The 6-month CBR was 61% (95% CI, 47 to 74) with tamoxifen plus everolimus and 42% (95% CI, 29 to 56) with tamoxifen alone. Time to progression (TTP) increased from 4.5 months with tamoxifen alone to 8.6 months with tamoxifen plus everolimus, corresponding to a 46% reduction in risk of progression with the combination (hazard ratio [HR], 0.54; 95% CI, 0.36 to 0.81). Risk of death was reduced by 55% with tamoxifen plus everolimus versus tamoxifen alone (HR, 0.45; 95% CI, 0.24 to 0.81). The main toxicities associated with tamoxifen plus everolimus were fatigue (72% v 53% with tamoxifen alone), stomatitis (56% v 7%), rash (44% v 7%), anorexia (43% v 18%), and diarrhea (39% v 11%). This study suggests that tamoxifen plus everolimus increased CBR, TTP, and overall survival compared with tamoxifen alone in postmenopausal women with AI-resistant mBC.

A phase II study of trastuzumab-DM1 (T-DM1), a HER2 antibody-drug conjugate (ADC), in patients (pts) with HER2+ metastatic breast cancer (MBC): Final results

1017 Background: T-DM1 is an ADC that combines the biological activity of trastuzumab (T) with targeted delivery of a potent antimicrotubule agent, DM1, to HER2-expressing cancer cells. In a phase I study, T-DM1 was administered IV q3w to pts with HER2+ MBC who had progressed on T + chemotherapy. T-DM1 was well-tolerated at the maximum tolerated dose (MTD) of 3.6 mg/kg, with no reports of cardiac toxicity. The confirmed objective response rate (ORR) for the 9 pts with measurable disease treated at the MTD was 44%. The phase II study described here further assesses tolerability and activity of T-DM1. Methods: This was a multi-institutional, open-label, single-arm phase II study, to enroll 100 pts. All eligible pts had progressed on HER2-directed therapy and had received chemotherapy in the metastatic setting. T-DM1 was administered at 3.6 mg/kg IV q3w. Primary objectives were assessment of ORR and of safety and tolerability. Results: As of the August 29, 2008, data-cut, 112 patients had enrolled, with baseline median age 54.5 (range 33–82); ECOG PS 2 or 3, 80%; 68.7% with &gt; 3 sites of metastatic disease; median 3 (range 1–14) prior chemotherapy agents for metastatic disease, median 76.3 weeks prior T, and 55.4% with previous lapatinib. Due to limited F/U, the median number of T-DM1 cycles received was 5 (range 1–16), and 19 of the 107 efficacy evaluable patients had only one post-baseline tumor assessment. Fifty-six pts had discontinued study treatment. With a median follow-up of 4.4 mos, there were 42 (39.3%) ORs (CR or PR), 29 (27.1%) of which have been confirmed by follow-up (F/U) imaging. Among the subgroup of pts who had either &gt;6 months F/U or had discontinued from the study at any time (n = 76) there were 33 ORs (43.4%), 29 (38.2%) of which were confirmed by F/U imaging. The most common grade 3–4 AE was thrombocytopenia (7.1%). Updated data will be presented at the meeting, including updated ORR, 6-month clinical benefit rate, ORR by independent review, progression-free survival, and duration of response. Conclusions: T-DM1 has single-agent activity in pts with previously treated, HER2+ MBC, and is well tolerated at the recommended phase II dose. [Table: see text]