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Rhabdomyosarcoma is the most common soft tissue sarcoma diagnosed in children and adolescents. Patients that are diagnosed with advanced or relapsed disease have exceptionally poor outcomes. The Children’s Oncology Group (COG) convened a rhabdomyosarcoma new agent task force in 2020 to systematically evaluate novel agents for inclusion in phase 2 or phase 3 clinical trials for patients diagnosed with rhabdomyosarcoma, following a similar effort for Ewing sarcoma. The task force was comprised of clinicians and basic scientists who collectively identified new agents for evaluation and prioritization in clinical trial testing. Here, we report the work of the task force including the framework upon which the decisions were rendered and review the top classes of agents that were discussed. Representative agents include poly-ADP-ribose polymerase (PARP) inhibitors in combination with cytotoxic agents, mitogen-activated protein kinase (MEK) inhibitors in combination with type 1 insulin-like growth factor receptor (IGFR1) inhibitors, histone deacetylase (HDAC) inhibitors, and novel cytotoxic agents.

Purpose. Osteosarcoma is a rare cancer and a third of patients who have completed primary treatment will develop osteosarcoma recurrence. The Src pathway has been implicated in the metastatic behavior of osteosarcoma; about 95% of samples examined express Src or have evidence of downstream activation of this pathway. Saracatinib (AZD0530) is a potent and selective Src kinase inhibitor that was evaluated in adults in Phase 1 studies. The primary goal of this study was to determine if treatment with saracatinib could increase progression-free survival (PFS) for patients who have undergone complete resection of osteosarcoma lung metastases in a double-blinded, placebo-controlled trial. Patients and Methods. Subjects with recurrent osteosarcoma localized to lung and who had complete surgical removal of all lung nodules were randomized within six weeks after complete surgical resection. Saracatinib, or placebo, was administered at a dose of 175 mg orally, once daily, for up to thirteen 28-day cycles. Results. Thirty-seven subjects were included in the analyses; 18 subjects were randomized to receive saracatinib and 19 to receive placebo. Intent-to-treat analysis demonstrated a median PFS of 19.4 months in the saracatinib treatment group and 8.6 months in the placebo treatment group (p=0.47). Median OS was not reached in either arm. Conclusions. Although saracatinib was well tolerated in this patient population, there was no apparent impact of the drug in this double-blinded, placebo-controlled trial on OS, and Src inhibition alone may not be sufficient to suppress metastatic progression in osteosarcoma. There is a suggestion of potential clinical benefit as evidenced by longer PFS in patients randomized to saracatinib based on limited numbers of patients treated.

TPS10591 Background: Osteosarcoma is a rare cancer and 33% of patients who have completed primary treatment will recur. The Src pathway has been implicated in the metastatic behavior of several tumors including osteosarcoma where 95% of samples express Src or have evidence of downstream activation of this pathway. Saracatinib (AZD0530) is a potent and selective Src kinase inhibitor. The recommended phase II dose in adults was found to be 175mg daily. The primary goal of this study is to determine if treatment with Saracatinib can increase progression free survival (PFS) for patients who have undergone complete resection of metastatic osteosarcoma nodules in the lung. Secondary goals are evaluation of overall survival, time to treatment failure, and evaluation of several biological correlatives. Methods: This is a multi-institutional, phase II.5, placebo-controlled study with an accrual goals of 88 randomized patients. Patients between 15 and 75 years, with histological confirmation of recurrent osteosarcoma, localized to the lung, who have potential for complete surgical resection, are eligible for enrollment. After complete resection, patients are randomized to treatment with saracatinib or placebo, of a daily oral dose of 175 mg, continuously for up to 1 year or until progression. Patients who recur in the lung while on-study and who are amenable to complete surgical resection will be un-blinded. Those patients who received placebo may have the option to undergo surgical resection. If fully resected, they will be offered therapy with saracatinib under the same treatment guidelines as above. As of January 2013, 38 patients have enrolled and 32 patients met the criteria to be randomized and began oral therapy with either saracatinib or placebo. An interim analysis is planned after 40 patients have been randomized. Clinical trial information: NCT00752206.

Purpose. There are no known effective medical treatments for refractory MPNST. Inactivation of the NF1 tumor suppressor in MPNST results in upregulation of mTOR (mammalian target of rapamycin) signaling and angiogenesis, which contributes to disease progression. We conducted a phase II study for patients (pts) with refractory MPNST combining everolimus (10 mg PO once daily) with bevacizumab (10 mg/kg IV every 2 weeks) to determine the clinical benefit rate (CBR) (complete response, partial response (PR), or stable disease (SD) ≥ 4 months). Patients and Methods. Patients ≥18 years old with chemotherapy refractory sporadic or NF1 MPNST were eligible. Tumor response was assessed after every 2 cycles (the WHO criteria). A two-stage design targeting a 25% CBR was used: if ≥ 1/15 pts in stage 1 responded, enrollment would be expanded by 10 pts, and if ≥ 4/25 patients had clinical benefit, the combination would be considered active. Results. Twenty-five pts, 17 with NF1 and 8 with sporadic MPNST, enrolled. One of 15 pts in stage 1 had clinical benefit. Of 10 additional pts enrolled, 2 had clinical benefit. The median number of completed cycles was 3 (range 1–16). Adverse events were similar to those known for this combination. Conclusion. With a CBR of 12% (3/25), the combination of everolimus and bevacizumab did not reach the study’s target response rate and is not considered active in refractory MPNST.

Abstract Background Axitinib is an oral small molecule that inhibits receptor tyrosine kinases vascular endothelial growth factor receptors 1 to 3. A phase 1 and pharmacokinetic (PK) trial evaluating axitinib was conducted in children with refractory solid tumors. Methods Axitinib was administered orally twice daily in continuous 28‐day cycles. Dose levels (2.4 mg/m 2 /dose and 3.2 mg/m 2 /dose) were evaluated using a rolling 6 design. Serial PKs (cycle 1, days 1 and 8) and exploratory biomarkers were analyzed. Results A total of 19 patients were enrolled; 1 patient was ineligible due to inadequate time having elapsed from prior therapy. The median age of the patients was 13.5 years (range, 5‐17 years). Two of 5 patients who were treated at dose level 2 experienced dose‐limiting toxicities (palmar‐plantar erythryodysesthesia syndrome in 1 patient and intratumoral hemorrhage in 1 patient). Frequent (>20%) grade 1 to 2 toxicities during cycle 1 included anemia, anorexia, fatigue, diarrhea, nausea, and hypertension. Nonhematological toxicities of grade ≥3 in subsequent cycles included hypertension and elevated serum lipase. PK analysis demonstrated variability in axitinib exposure, the median time to peak plasma concentration was 2 hours, and the half‐life ranged from 0.7 to 5.2 hours. Exposure and dose were not found to be significantly associated with hypertension. Five patients achieved stable disease for ≥6 cycles as their best response, including patients with malignant peripheral nerve sheath tumor (1 patient), Ewing sarcoma (1 patient), hepatocellular carcinoma (1 patient), and osteosarcoma (2 patients). One patient with alveolar soft part sarcoma achieved a partial response. Kidney injury biomarkers were found to be elevated at baseline; no trends were identified. Conclusions In children with refractory solid tumors, the maximum tolerated and recommended dose of axitinib appears to be 2.4 mg/m 2 /dose, which provides PK exposures similar to those of adults.