Radiolabeled OTSA101, a monoclonal antibody targeting synovial sarcoma (SS) developed by OncoTherapy Science, was used to treat relapsing SS metastases following a theranostic procedure: in case of significant 111In-OTSA101 tumor uptake and favorable biodistribution, patient was randomly treated with 370/1110 MBq 90Y-OTSA101. Monte Carlo-based 3D dosimetry integrating time-activity curves in VOI was performed on 111In-OTSA101 repeated SPECT/CT. Estimated absorbed doses (AD) in normal tissues were compared to biological side effects and to the admitted maximal tolerated absorbed dose (MTD) in normal organs. Results in the tumors were also compared to disease evolution. Biodistribution and tracer quantification were analyzed on repeated SPECT/CT acquisitions performed after injection of 111In-OTSA101 in 19/20 included patients. SPECT images were warped to a common coordinates system with deformable registration. Volumes of interest (VOI) for various lesions and normal tissues were drawn on the first CT acquisition and reported to all the SPECT images. Tracer quantification and residence time of 111In-OTSA101 in VOI were used to evaluate the estimated absorbed doses per MBq of 90Y-OTSA101 by means of Monte Carlo simulations (GATE). A visual scale analysis was applied to assess tumor uptake (grades 0 to 4) and results were compared to the automated quantification. Results were then compared to biological side effects reported in the selected patients treated with 90Y-OTSA101 but also to disease response to treatment. After screening, 8/20 patients were treated with 370 or 1110 MBq 90Y-OTSA101. All demonstrated medullary toxicity, only one presented with transient grade 3 liver toxicity due to disease progression, and two patients presented with transient grade 1 renal toxicity. Median absorbed doses were the highest in the liver (median, 0.64 cGy/MBq; [0.27 −1.07]) being far lower than the 20 Gy liver MTD, and the lowest in bone marrow (median, 0.09 cGy/MBq; [0.02 −0.18]) being closer to the 2 Gy bone marrow MTD. Most of the patients demonstrated progressive disease on RECIST criteria during patient follow-up. 111In-OTSA101 tumors tracer uptake visually appeared highly heterogeneous in inter- and intra-patient analyses, independently of tumor sizes, with variable kinetics. The majority of visual grades corresponded to the automated computed ones. Estimated absorbed doses in the 95 supra-centimetric selected lesions ranged from 0.01 to 0.71 cGy per injected MBq (median, 0.22 cGy/MBq). The maximal tumor AD obtained was 11.5 Gy. 3D dosimetry results can explain the observed toxicity and tumors response. Despite an intense visual 111In-OTSA101 liver uptake, liver toxicity was not the dose limiting factor conversely to bone marrow toxicity. Even though tumors 111In-OTSA101 avidity was visually obvious for treated patients, the low estimated tumors AD obtained by 3D dosimetry explain the lack of tumor response.

Background: MOST-plus is a multicenter, randomized, open-label, adaptive Phase II trial evaluating the clinical benefit of targeted treatments matched to molecular alteration in advanced/metastatic solid tumors. Sorafenib was tested on patients with tumors harboring sorafenib-targeted genes. Methods: The MOST-plus trial used a randomized discontinuation design. After 12 weeks of sorafenib (400 mg, po BID), patients with progressive disease discontinued study, patients with objective response were proposed to continue sorafenib, whereas patients with stable disease (SD) were randomly assigned (1:1) to the maintenance or interruption of treatment. The primary endpoint was RECIST version 1.1 progression-free rate at 16 weeks after randomization (PFR-16w). Secondary endpoints included progression-free survival (PFS), overall survival (OS), and toxicity. Statistical analyses used a sequential Bayesian approach with interim efficacy analyses. The enrolment could be stopped in the case of a 95% probability for the estimated PFR-16w to be higher in the maintenance than in the interruption arm (NCT02029001). Results: 151 patients were included, of whom 35 had SD at 12 weeks of Sorafenib. For the 35 patients with SD on sorafenib, the PFR-16w was 65% [95% credibility interval 43.4–83.7] in the continuation arm and 25% [7.8–48.1] in the interruption arm. Median PFS and OS were improved in the maintenance versus the interruption arm (mPFS: 5.6 [95%CI 1.97–6.77] months versus 2.0 [95%CI 1.61–3.91] months (p = 0.0231) and mOS: 14.3 [95%CI 8.9–23.8] versus 8.0 months [95%CI 3.5–15.2] (p = 0.0857)). Conclusion: Sorafenib showed activity in progressive patients with solid tumors harboring somatic genomic alterations in sorafenib-targeted genes. Continuing sorafenib when SD is achieved improves PFR compared to interruption.

11054 Background: Advanced SyS are rare tumors with limited curative options. FZD10 is highly expressed in SyS but not in normal adult tissue. OTSA101 is a MAb targeting FZD10, labelled with a radioisotope. Methods: We conducted a phase I, FIH study including adult pts with advanced, refractory SyS. In part 1, pts received OTSA101 labelled with In¹¹¹ used as radiotracer to assess biodistribution and tumor uptake. In part 2, pts with significant tumor uptake were randomized to receive OTSA101 labelled with 370MBq of Y⁹⁰ (Arm A) or 1110MBq Y⁹⁰ (Arm B). Primary endpoints were occurrence of unacceptable biodistribution /lack of tumor uptake in part 1 and occurrence of related adverse events (AEs) Grade ≥ 3 during the first 8 weeks following injection of Y⁹⁰OTSA101 in part 2. Responses were assessed per RECIST 1.1. Results: From January 2012 to June 2015, 20 pts (10 females, median age 43, range 21-67) with advanced SyS were enrolled. Ten pts (50%) had sufficient tumor uptake to proceed to part 2 and 8 were randomized (Arm A: 3 and Arm B: 5). Two pts were not randomized due to worsening PS. During part 2, the most common Grade ≥ 3 AEs were haematological, including reversible lymphopenia, thrombocytopenia and neutropenia, and were more common in Arm B. One pt with SD after 12 weeks received a 2^nd injection of ⁹⁰Y-OTSA101, but experienced fatal hemoptysis. No objective response was observed. Best response was SD in 5/8 pts lasting up to 21 weeks for 1 pt. Conclusions: This FIH shows that radioimmunotherapy targeting FZD10 is feasible and safe in SyS pts. Tumor uptake was heterogeneous but sufficient to select 50% of pts for ⁹⁰Y-OTSA101 treatment. Due to limited sample size, further clinical investigations are needed to assess the therapeutic activity of ⁹⁰Y-OTSA101 with a recommended dose of 1110MBq of ⁹⁰Y. Clinical trial information: NCT01469975.

TPS2083 Background: Therapeutic options are limited for refractory/relapsed adult medulloblastoma with activation of sonic hedgehog pathway (SHH-MB). Inhibition of this pathway may offer an attractive therapy. Vismodegib suppresses SHH signaling by binding to and interfering with the SMO transmembrane receptor. We postulate that vismodegib together with chemotherapy may kill more tumor cells than chemotherapy alone by blocking cell proliferation at different molecular levels (vertical association strategy). Methods: MEVITEM is a multicenter, randomized (2:1 ratio), open-label, Phase I/II aiming to evaluate the safety and clinical activity of the association vismodegib (V: daily 150mg/d) + temozolomide (T: D-5: 150 mg/m² for Cycle 1 and 200 mg/m² for subsequent cycles) versus T alone in adult patients with recurrent/refractory SHH-MB. Main eligibility criteria are: histologically confirmed recurrent/refractory SHH-MB for which no known curative therapy exists, not previously treated with T, with evidence of measurable disease and documented activation of SHH pathway. Pathological review and SHH pathway analysis are performed centrally by IHC. This Phase I/II includes i) a safety run aiming to evaluate the safety of V+T and ii) a Phase II part aiming to evaluate the clinical activity of V+T measured by the 6-month non-progression rate. Patients enrolled in the safety run are included in the evaluation of the Phase II part. Considering that V+T would be uninteresting if 6-month non-progression rate ≤ 30% and promising if ≥ 55% and using Simon’s optimal two-stage design (type I error rate:5%, power:80%), a sample size of 25 evaluable patients is required for Arm V+T (including 9 in stage I). The sample size in Arm T alone is 13 patients. Considering the rarity of SHH-MB, the few therapeutic options and the promising results reported with V in SHH-MB: the Sponsor considered the enrolment of patients previously treated by T in a 3^rdindependent and parallel arm with V as single agent (Arm V). To date, 18 patients were enrolled (Arm V+T: 7, Arm T: 4, Arm V: 7), the Phase II part is ongoing. Clinical trial information: NCT02029001.