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TPS10066 Background: Genomic alterations in the RET kinase, including gene fusions and activating point mutations, are implicated in the pathogenesis of lung, thyroid, sarcoma and other cancers in both chidren and adults. Currently available multikinase inhibitors with anti-RET activity are non-selective and may be associated with less favorable toxicity profile. LOXO-292 is a novel, highly selective, ATP-competitive small molecule RET inhibitor. LOXO-292 has preclinical nanomolar potency against diverse RET alterations (e.g. fusions, activating mutations and anticipated acquired resistance mutations) and anti-tumor activity in the brain. LOXO-292 has demonstrated clinical activity in adult patients with RET-alterated solid tumors. Methods: LIBRETTO-121 (EudraCT 2019-000212-28) is an ongoing multicenter phase 1/2 dose escalation multicenter trial in patients 6 months-21 years of age with advanced, RET-altered solid and CNS tumors. Dose escalation follows a rolling 6 design starting at the equivalent of the adult recommended phase 2 dose. Enrollment began on 12 Feb 2019 and is ongoing. Key eligibility criteria include: solid or CNS tumor with a documented RET gene alteration refractory to standard therapy; age 6 months to 21 years of age; and adequate bone marrow, liver and kidney function. LOXO-292 is administered orally BID for continuous 28-day cycles. Both capsule and liquid suspension dosage forms are available. The primary objective of the phase 1 portion of the study is to determine safety and dose limiting toxicities. Key secondary objectives include characterization of pharmacokinetic properties, identification of the MTD and initial characterization of the anti-tumor activity of LOXO-292. Archival tissue will be used to further characterize molecular abnormalities. Clinical trial information: 2019-000212-28.

2006 Background: TRK fusions are oncogenic drivers of a variety of cancers, many of which can involve the central nervous system (CNS). Larotrectinib is an FDA-approved selective TRK inhibitor for the treatment of TRK fusion cancer (Drilon et al, NEJM 2018). While larotrectinib has been shown to cross the blood–brain barrier (Ziegler et al, Br J Cancer 2018), its clinical activity in a series of TRK fusion cancers with primary or metastatic intracranial disease has not been described. Methods: Patients (pts) with non-primary CNS solid tumors with brain metastases, or primary CNS tumors harboring a TRK fusion treated with larotrectinib in 2 clinical trials (NCT02637687, NCT02576431) were identified. Larotrectinib was administered until disease progression (PD), withdrawal, or unacceptable toxicity. Disease status was investigator-assessed (RANO and RECIST). Data cutoff: July 30, 2018. Results: 14 pts were identified: 5 non-primary CNS solid tumors (3 lung cancer, 2 thyroid cancer; fusion type: 2 ETV6-NTRK3, 2 SQSTM1-NTRK3, 1 EPS15-NTRK1; age range 25–79 y) and 9 primary CNS tumors (3 glioma, 2 glioblastoma, 1 astrocytoma, 3 NOS; fusion type: 3 BCR-NTRK2, 2 KANK-NTRK2, 1 each of AFAP1-NTRK1, AGTPBP1-NTRK2, ETV6-NTRK3, SPECC1L-NTRK2; age range 2–79 y). In the 5 pts with non-primary CNS tumors, the best objective response to therapy was PR in 3 (60%, 1 pending confirmation), SD in 1 (20%), and not evaluable (NE) in 1 (20%). Duration of response ranged from 9+ to 13 mo. In the 9 pts with primary CNS tumors, disease control was achieved in all evaluable pts (primary PD not observed; 1 pt required dose increase). The best objective response to therapy was PR in 1 (11%; pending confirmation, −55% tumor shrinkage, ongoing at 3.7 mo), SD in 7 (78%; tumor shrinkage range −1% to −24% for pts with measurable disease, 5 had SD > 4 mo), and NE in 1 (11%). Duration of treatment ranged from 2.8–9.2+ mo. Conclusions: Larotrectinib is active in pts with TRK fusion cancers with intracranial disease. Confirmed responses and durable disease control were seen in metastatic disease and primary CNS tumors of various histologies. These results further support expanded testing for TRK fusions across all cancers, including primary CNS tumors. Clinical trial information: NCT02637687 and NCT02576431.

10010 Background: TRK fusions involving NTRK1, NTRK2, and NTRK3 genes have been identified in a broad range of pediatric and adult malignancies. Larotrectinib, a highly-selective oral TRK inhibitor, was well tolerated and showed encouraging antitumor activity in 17 pediatric patients (pts) with TRK fusion cancer (Laetsch et al, Lancet Oncol 2018). Here, we present data on the clinical efficacy and safety of larotrectinib in 38 pediatric pts with TRK fusion cancer from an expanded dataset. Methods: Pediatric pts enrolled in two larotrectinib clinical trials (NCT02637687, NCT02576431) with TRK fusion cancer detected by local testing were included; pts with primary CNS tumors were excluded from this report. Larotrectinib was administered until complete surgical resection, disease progression, withdrawal, or unacceptable toxicity. Disease status was investigator-assessed using RECIST v1.1. Data cutoff: July 30, 2018. Results: As of July 30, 2018, 38 children and adolescents < 18 y with TRK fusion cancer were enrolled. Median age was 2.3 y (range 0.1–14.0); 14 (37%) were < 1 y. 18 (47%) had infantile fibrosarcoma, 15 (39%) other soft tissue sarcoma, 2 (5%) thyroid cancer and 1 (3%) each had gastrointestinal stromal tumor, melanoma, or mesoblastic nephroma. TRK fusions involved NTRK1, 2, and 3 in 18 (47%), 2 (5%), and 18 (47%) pts, respectively. Half of the pts had metastatic disease and half locally advanced disease at entry. 26 pts (68%) had received prior systemic therapy (median lines: 1 [range 0–4]) and 6 were treatment-naïve. In 34 evaluable pts, the overall response rate was 94%: 12 CRs, 18 confirmed PRs, and 2 PRs pending confirmation; 2 had stable disease. Median duration of response had not been reached (range 1.6+ to 26.7+ months); 84% > 1 y. At data cutoff, 28 pts (74%) remained on treatment; 4 pts discontinued due to complete surgical resection and 4 due to disease progression while on therapy, 2 of whom initially responded (PR). Adverse events were mostly grade 1–2. Conclusions: Larotrectinib treatment resulted in a high and durable response rate in pediatric pts with TRK fusion cancer together with a favorable safety profile. Routine testing for NTRK gene fusions in pediatric cancer pts is recommended in the appropriate clinical context. Clinical trial information: NCT02637687 and NCT02576431.

10045 Background: Genomic alterations of RET kinase, including chromosomal fusions and activating point mutations, have been identified as oncogenic drivers in pediatric and adult cancers. Multikinase inhibitors have modest activity against RET-altered cancers and are associated with significant toxicity. LOXO-292 is a potent, ATP-competitive, small molecule RET inhibitor with high selectivity for RET, preclinical activity in the brain and excellent pharmacokinetic properties. In an ongoing phase 1/2 study of adult and adolescent patients with advanced RET-altered cancers, LOXO-292 demonstrated marked antitumor activity and was well tolerated. Methods: Pediatric patients with RET-altered cancers who were unable to access LOXO-292 through a phase 1/2 clinical trial were enrolled using FDA-allowed, IRB-approved single patient protocols . Patients received LOXO-292 (capsule/liquid formulation) orally, continuously, at a starting dose of 90 mg/m2 BID. Response was assessed locally by investigators. Results: As of January 31, 2019, 4 female patients aged 13 months–8 years were enrolled from the Republic of Korea (papillary thyroid cancer, n = 1) and the USA (infantile myofibroma/hemangiopericytoma, n = 1; congenital mesoblastic nephroma/infantile fibrosarcoma, n = 1; lipofibromatosis, n = 1). All tumors harbored RET gene fusions (5′ partners: CCDC6, MYH10, SPECC1L, and NCOA4, respectively), detected by next-generation sequencing. Previous therapies included surgery/iodine 131 (n = 1); vandetanib (n = 1); surgery/chemotherapy (n = 1); 1 patient was treatment-naïve. Duration of treatment ranged from 3–120 days and all patients remain on treatment. There were no dose modifications or discontinuations due to adverse events. There were no treatment-related adverse events ≥ grade 3. Two patients who were evaluable for response had partial responses (both ongoing, 1 confirmed, 1 pending confirmation). Conclusions: These preliminary data from a real-world setting suggest that LOXO-292 is effective and safe in pediatric patients whose tumors harbor RET gene fusions.

PurposeInterest in the use of herbal products has grown dramatically in the Western world. Recent estimates suggest an overall prevalence for herbal preparation use of 13% to 63% among cancer patients. With the narrow therapeutic range associated with most anticancer drugs, there is an increasing need for understanding possible adverse drug interactions in medical oncology.MethodsIn this article, a literature overview is provided of known or suspected interactions of the 15 best-selling herbs in the United States with conventional allopathic therapies for cancer.ResultsHerbs with the potential to significantly modulate the activity of drug-metabolizing enzymes (notably cytochrome P450 isozymes) and/or the drug transporter P-glycoprotein include garlic (Allium sativum), ginkgo (Ginkgo biloba), echinacea (Echinacea purpurea), ginseng (Panax ginseng), St John's wort (Hypericum perforatum), and kava (Piper methysticum). All of these products participate in potential pharmacokinetic interactions with anticancer drugs.ConclusionIt is suggested that health care professionals and consumers should be aware of the potential for adverse interactions with these herbs, question their patients on their use of them, especially among patients whose disease is not responding to treatments as expected, and urge patients to avoid herbs that could confound their cancer care.

10510 Background: Larotrectinib is the first selective small-molecule inhibitor of TRKA, B, and C in clinical development. Data from the adult phase I trial demonstrate prolonged responses in patients (pts) with TRK fusions and a favorable tolerability profile. Methods: This multicenter, rolling 6 phase I study enrolled pts with refractory solid or CNS tumors aged ≥ 1 month – 21 years. Pts were dosed orally BID on a continuous 28-day schedule either by capsule or solution. Pharmacokinetic (PK)-directed intra-subject dose escalation was permitted, with exposures targeting the adult recommended Phase II dose (RP2D) of 100 mg BID. The primary objective was to define the MTD / RP2D; secondary objectives included PK and efficacy using RECIST v1.1. Results: As of December 31, 2016, 17 pts (12 with TRK fusions, 5 without TRK fusions) with a median age of 5.2 years (0.4 – 18.3) were enrolled to 3 dose levels. Pts were enrolled with fusions of all 3 NTRK genes: NTRK1 (n=6), NTRK2 (n=1), and NTRK3 (n=5) in heterogeneous tumor diagnoses: infantile fibrosarcoma (IFS) (n=6), other sarcoma (n=4), and papillary thyroid cancer (n=2). Most common AEs regardless of attribution were vomiting, diarrhea, and fatigue. While 8 (47%) pts experienced grade 3-4 AEs, none were attributed to larotrectinib. No DLTs were observed and an MTD was not established. Both formulations delivered dose-dependent PK comparable to the adult RP2D at dose level 3. 12 pts (10 with TRK fusions, 2 without TRK fusions) remain on treatment with median follow-up of 2.8 months (0.7 – 8.4). Among TRK fusion pts, the vast majority have achieved confirmed RECIST responses regardless of tumor diagnoses. No responses were seen in pts without TRK fusions (n=4). 5 pts discontinued therapy, including 2 with TRK fusions: 1 pt with IFS had sufficient response to allow tumor resection, and 1 pt with IFS progressed with a documented acquired resistance mutation. Conclusions: Larotrectinib has demonstrated a favorable tolerability profile and histology-independent efficacy in pediatric pts harboring TRK fusions. Updated safety and efficacy data will be presented, including the RP2D, response rate, duration of response, and use of larotrectinib in the pre-surgical setting. Clinical trial information: NCT02637687.

LBA2501 Background: Larotrectinib is the first selective small-molecule pan-TRK inhibitor. TRK fusions appear oncogenic independent of tumor lineage, are widely distributed across cancers, and affect all ages. We present an integrated dataset from 3 studies intended to support regulatory approval. Methods: All NTRK fusion pts with RECIST measurable disease enrolled to the adult (NCT02122913, n=8) and pediatric (NCT02637687, n=12) phase I trials and adult/adolescent phase 2 trial (NCT02576431, n=35) were analyzed. TRK fusion status was determined by local testing prior to enrollment. Pts were dosed predominantly at 100mg BID on a continuous 28-day schedule. Primary objective was investigator-assessed overall response rate (ORR) per RECIST v1.1. Secondary endpoints included duration of response (DOR) and safety. Data were cut on 31-JAN-2017. Results: 55 TRK fusion pts (12 peds, 43 adult, range: 4 mo.-76 yrs) were enrolled (median priors=2). Fusions involved NTRK1 (n=25), NTRK2 (n=1), and NTRK3 (n=29), and 14 unique partners. 13 discrete tumor types were treated: salivary (12), sarcoma (10), infantile fibrosarcoma (7), lung (5), thyroid (5), colon (4), melanoma (4), cholangio (2), GIST (2), and other (4). For the 46 pts evaluated to date, the ORR was 78% (95% CI: 64%–89%) with responses in 12 unique tumor types. Responses are ongoing in 29/33 (88%) pts, excluding 3 peds pts whose DOR was censored at attempted curative resection. A median DOR has not been reached as the majority of responders remain on treatment without progression. The longest responder remains on treatment at 23 mos., 8 pts remain in response at >12 mos., and 16 pts at >6 mos. NTRK solvent front mutations were detected in all 4 pts to develop acquired resistance. The most common TEAEs were fatigue (30%), dizziness (28%), and nausea (28%). 5 (11%) pts required dose reductions. Conclusions: Larotrectinib has demonstrated consistent and durable antitumor activity in TRK fusion cancers, across a wide range of ages and tumor types, and was well-tolerated. Larotrectinib could be the first targeted therapy developed in a tissue type-agnostic manner, and the first developed simultaneously in adults and pediatrics. Clinical trial information: NCT02576431, NCT02122913, NCT02637687.

TPS10583Background: The TRK family of neurotrophin receptors, TRKA, TRKB, and TRKC (encoded by NTRK1, NTRK2, and NTRK3 genes, respectively) and their neurotrophin ligands regulate growth, different...

651 Background: Ixabepilone, an epothilone B analog, stabilizes microtubules by binding to tubulin. The response rate (RR) in taxane-pretreated patients at our institution was 22%. Methods: Patients (pts) were eligible if they had MBC previously untreated with taxanes and measurable disease by RECIST criteria. Ixabepilone was given at 6mg/m2/d intravenously days 1–5 every 3 weeks until unacceptable toxicity or disease progression. Primary objectives included RR and toxicity. Pts underwent pre and/or post treatment tumor biopsies for correlative studies. Acetylated α-tubulin, Tau-1, and p53 were stained with anti-acetylated α-tubulin, anti-Tau-1, and anti-p53 antibodies in samples from 13 pts. Staining was scored quantitatively using the Automated Cellular Imaging System. Results: Twenty-three pts received 197 cycles (C). Median of 7C (range 2–22) per pt were administered. Median age was 55 (range 22–79). Seven pts received 1 prior metastatic chemotherapy regimen. Ten of 23 or 43% (exact 95% confidence interval: 23.2% to 65.5%) pts had partial responses (PR), 9 (39%) stable disease (SD) (2 unconfirmed PRs), and 4 (17%) progressive disease (PD). Median time to progression was 5.3 months; median duration of response was 5.4 months from date of best response. Four pts required dose reductions for neutropenia, neuropathy or fatigue. Grade 3/4 toxicities included neutropenia (22%), fatigue (13%), anorexia (9%), infection without neutropenia (9%), motor neuropathy (4%), and muscle weakness (4%). No grade 3/4 sensory neuropathy was seen, but 35% and 13% of pts had grades 1 and 2 neuropathy respectively. Median acetylated α-tubulin at baseline was 0.2 in responders and 17.6 in non-responders (p=0.069). There were no differences in response according to Tau-1 or p53 expression at baseline. Conclusion: Ixabepilone is an effective treatment for MBC with a 43% RR in 23 pts previously untreated with taxanes. There was minimal hematologic toxicity and no grade 3 sensory neuropathy. The use of baseline level of acetylated α-tubulin to predict response may warrant further study. No significant financial relationships to disclose.

4553 Purpose: We evaluated whether the time to return to the baseline prostate-specific antigen level (PSA response duration) was significantly associated with time to death following randomization...