Real‐world experience of tyrosine kinase inhibitors in children, adolescents and adults with relapsed or refractory bone tumours: A Canadian Sarcoma Research and Clinical Collaboration (CanSaRCC) study

Abstract Objectives We conducted a retrospective multi‐centre study to assess the real‐world outcome of regorafenib (REGO) and cabozantinib (CABO) in recurrent/refractory bone tumours (BTs) including osteosarcoma (OST), Ewing sarcoma (EWS) and chondrosarcoma (CS)/extra‐skeletal mesenchymal CS (ESMC). Methods After regulatory approval, data from patients with recurrent BT (11 institutions) were extracted from CanSaRCC (Canadian Sarcoma Research and Clinical Collaboration) database. Patient characteristics, treatment and outcomes were collected. Progression‐free survival (PFS) and overall survival (OS) were estimated using the Kaplan–Meier method. Results From July 2018 to May 2022, 66 patients received REGO or CABO; 39 OST, 18 EWS, 4 CS and 5 ESMC. Median age was 27.8 years (range 12–76); median starting dose was 60 mg for CABO (n = 37, range 40–60) and 120 mg for REGO (n = 29, range 40–160). Twenty‐eight (42.4%) patients required dose reduction: hand‐foot syndrome 7 (10.6%), nausea/vomiting 1 (1.5%), diarrhoea 1 (1.5%), 2 elevated LFTs (3%), elevated bilirubin 1 (1.5%) and mucositis 1 (1.5%). The median OS for patients with OST, EWS, CS and ESMC was 8.5 months (n = 39, 95% CI 7–13.1); 13.4 months (n = 18, 95% CI 3.4–27.2), 8.1 (n = 4, 95% CI 4.1–9.3) and 18.2 (n = 5, 95% CI (10.4–na), respectively. Median PFS for OST, EWS, CS and ECMS was 3.5 (n = 39, 95% CI 2.8–5), 3.9 (n = 18, 95% CI 2.1–5.9), 5.53 (n = 4. 95% CI 2.13–NA) and 11.4 (n = 5, 95% CI 1.83–14.7), respectively. Age, line of therapy, REGO versus CABO, or time from diagnosis to initiation of TKI were not associated with PFS on univariable analysis. Conclusion Our real‐world data show that TKIs have meaningful activity in recurrent BT with acceptable toxicities when started at modified dosing. Inclusion of TKIs in earlier lines of treatment and/or maintenance therapy could be questions for future research.


| INTRODUCTION
Bone tumours account for less than 1% of diagnosed cancers every year.The most common primary bone tumours include osteosarcoma (OST), Ewing sarcoma (EWS) and chondrosarcoma (CS).The management of EWS and OS includes aggressive surgery and/or radiation in combination with chemotherapy.Surgery remains the only curative option for CS.Despite multimodality therapy, at least 30%-40% of patients will experience relapse of their disease.Patients with large or axial tumours and those with high burden of distant metastases at diagnosis have the highest risk of recurrence.There is a lack of effective treatment options for recurrent bone tumours and there remains an urgent unmet medical need. 1,2epending on location and timing of relapse, traditional approaches to second line therapy have been dominated by cytotoxic chemotherapies. 3,46][7][8] Tyrosine kinases are key signalling proteins involved in cell growth and metastasis. 9nhibition of these proteins have shown relevant implications regarding therapeutics in sarcoma. 10abozantinib (CABO) is a multi-TKI targeting MET, VEGFR2, RET, KIT, FLT3, TIE2 and AXL, with important activity in several cancers such as renal cell carcinoma and prostate cancer. 11,12In a phase II study involving children and adults with relapsed or advanced OST and EWS, partial responses were seen in 10 (26%; 95% CI 13-42) of 39 EWS patients and 5 (12%; 95% CI 4-26) of 42 OST patients 5 at dose of 60 mg in adults and 40 mg/m 2 in children, orally once daily in 28-day cycles.Regorafenib (REGO) is another multi-targeted TKI which was evaluated in a phase II study of 42 adults with relapsed OST.The initial dose of REGOwas 160 mg orally for Days 1-21 of a 28-day cycle.Here, median progression-free survival (PFS) was significantly improved among those who received REGO compared with placebo with a PFS of 3.6 months (95% CI, 2.0-7.6 months) versus 1.7 months (95% CI, 1.2-1.8months), respectively (HR 0.42; 95% CI, 0.21-0.85;p = 0.017). 13Similar benefit compared to placebo was noted in a French study of 43 adults with OST. 8 In the same study, a cohort of adults with CS also derived benefit from REGO with a PFS of 19.9 weeks compared with 8 weeks on placebo. 14Notably, both CABO and REGO offered patients an oral drug option with manageable toxicity and meaningful activity, addressing an area of significant clinical and patient need.Real-world evidence for the use of these medications is not yet known.
Herein, we use a newly formed national database platform called CanSaRCC (Canadian Sarcoma Research and Clinical Collaboration) to report experience using CABO and REGO in children and adults with relapsed or refractory bone tumours to add real-world evidence to these initial trials.

Conclusion:
Our real-world data show that TKIs have meaningful activity in recurrent BT with acceptable toxicities when started at modified dosing.Inclusion of TKIs in earlier lines of treatment and/or maintenance therapy could be questions for future research.

K E Y W O R D S
cabozantanib, CanSaRCC, chondrosarcoma, Ewing sarcoma, osteosarcoma, regorafenib After research ethics board approval at the following 11 institutions: The Hospital for Sick Children (Toronto), Princess Margaret Cancer Centre (Toronto), Mount Sinai Hospital (Toronto), BC Children's Hospital (Vancouver), BC Cancer (British Columbia), Hôpital Maisonneuve Rosemont (Montreal), Centre Hospitalier Universitaire de Québec (Québec City), the McGill University Health Centre (Montreal), Alberta Health Services (Edmonton), CancerCare Manitoba (Winnipeg), the Saskatchewan Health Authority (Saskatchewan), patient data were collated into the CanSaRCC database.Patients of all ages with documented relapsed or refractory OST, EWS or CS who received either CABO or REGO for at least 4 weeks were between July 2018 and May 2022 were included.All patients had measurable disease at the time of initiation of TKI therapy.Patients' demographics, disease and treatment details were then collected using a case report form and summarized using descriptive statistics.Treatment-related toxicities were graded according to CTCAEv5.Response assessment was performed by local investigators.PFS and overall survival (OS) were estimated using the Kaplan-Meier method and compared using logrank test.PFS was calculated from the date of initiation of the TKI to the date of disease progression or death as determined by the local investigator.Disease progression or death from the disease was considered an event for PFS.OS was calculated from the date the patient started the TKI to the date of last follow-up (including death).Clinical benefit rate (CBR) was defined as complete response (CR) plus partial response (PR) plus stable disease (SD) > 3 months.Univariable (UVA) analyses were conducted to examine the association of patient-, disease-and treatment-related variables with outcomes of PFS, OS and length of TKI therapy (TKI start to TKI end, if continuous then TKI start to last FU/ death).We used student's t-test/ANOVA and/or Wilcoxon rank/Kruskal-Wallis tests to compare means and medians between groups.Chi-square test was used to compare categorical variables.For all analyses, p value <0.05 was considered statistically significant.Statistics were performed using SAS version 9.4.
3.2 | Treatment, dose reductions and toxicity
Based on the data collected, no patients on CABO nor REGO discontinued treatment due to toxicity.
There were two exceptional responders in our cohort.Case 1 is that of a 27-year-old female with OST, who suffered a relapse 12 years following her initial diagnosis (at which time she was treated with MAP chemotherapy) with an intracardiac mass causing severe right ventricular outflow tract obstruction and bilateral lung metastases.After urgent cardiac debulking, she received 5 cycles of ifosfamide/etoposide with good response.She was started on REGO due to persistent small lung lesions (largest 1.6 × 1.1 cm, 1.0 × 0.9 cm) and remains on drug without progression for 16.1 months at the data cut off for study.The second case is that of an 18-year-old male with OST who developed bilateral small volume pulmonary metastases (largest 1.1 × 0.6 cm) less than 2 years from primary diagnosis, who started CABO at first relapse and remains on drug without progression for 16.6 months.

| DISCUSSION
Using the recently established infrastructure of a national sarcoma database, herein we present meaningful real-world activity data of REGO and CABO in children, adolescents and adults with relapsed or refractory bone tumours.Oral TKIs offer patients a viable alternative to cytotoxic chemotherapy offering reprieve from alopecia, nausea and cytopenia, and in select cases, is associated with long term disease stability.Patients either started TKI at doses lower than previously published or required dose reductions highlighting the lack of clarity around the ideal therapeutic window of TKI in bone tumours.
The outcome for patients with advanced bone tumours has remained stagnant over the last 40 years, 15 and although the essential components of induction therapy including definitive local control and some amount of cytotoxic chemotherapy remain, dose intensification or addition of other chemotherapy agents have failed to offer solutions. 16Considering prolonged disease stability observed in some patients, especially for those in whom TKI was started early, offering TKI in first relapse may be an important strategy to consider moving forward.Due to low power, we were unable to F I G U R E 1 Progression-free survival (PFS) of 66 patients with recurrent or refractory bone tumours treated either with regorafenib (A) or with cabozantinib (B).Osteosarcoma (Blue), chondrosarcoma (Red), Ewing's sarcoma (Green) and Extra-skeletal mesenchymal CS (Brown).
T A B L E 2 Outcome of study population (n = 66).prove statistical significance that line of therapy impacted outcome.The PFS seen in our cohort is comparable to those described in the seminal studies of REGO and CABO, 5,8,13,14 although our series excluded patients who were on drug for less than 4 weeks and events were not centrally reviewed.CBR is an important outcome to patients reflecting the ability to stay on life prolonging treatment.Thus, TKI for maintenance treatment to delay subsequent progression may be important to consider in bone tumours, although this was not done in our current series.Previously, maintenance therapy with an mTOR inhibitor, ridaforolimus in adults with soft tissue or bone sarcoma was explored, although with minimal clinical benefit. 17In comparison, maintenance chemotherapy does in fact improve survival in soft tissue rhabdomyosarcoma. 18Further studies are needed to precisely identify the role of maintenance TKI therapy in bone tumours and we look forward to the results of an ongoing trial evaluating CABO maintenance therapy in high-risk sarcoma (clini caltr ials.govidentifier NCT05135975 This study included patients of all ages, and we observed variability in dosing practices across ages and institutions.Many paediatric patients were treated with flat dosing instead of dosing per m 2 .Moreover, the starting dose of CABO was only 40 mg in half of the adult patients (13/30) and median dose of REGO was 120 mg for all patients.In four paediatric patients, REGO was started at 40 mg and dose slowly increased to tolerance.We suggest exploring a 'go slow' approach to maximize tolerance to drug, a strategy similar to that implemented in other cancers. 19S is a rare form of bone cancer that is mainly treated with surgery and is generally unresponsive to traditional chemotherapy options. 20  the receptor pathway has been suggested to delay tumour growth supporting the rational to study TKIs in this sarcoma subset. 21In the REGOBONE trial, patients with CS responded to REGO even after having received chemotherapy for relapsed disease.In our series, five of nine patients with CS had ESMC (four confirmed HEY1-NCOA2 gene fusion) who experienced prolonged disease control with TKI, similar to prior reports. 22Interestingly, the main downstream targets of HEY1-NCOA2 include PDGFRA, PDGFRB and BCL2 perhaps contributing to the sensitivity to TKI. 23 Other TKIs have been examined in recurrent/refractory bone tumours including sorafenib in OST (PFS 4 (95% CI 2-5)), 24 and sorafenib plus everolimus (significant toxicity). 25,26In the current study, we did not evaluate the outcome of patients who may have received sorafenib for OST.

Regorafenib (n
This study was conducted using a national database (Canadian Sarcoma Research and Clinical Collaboration) that permitted the capture of data for patients with sarcoma diagnosed across a wide geographical area and facilitated meaningful analysis on a rare subset of patients.This infrastructure that includes pre-defined data elements, quality check and longitudinal follow-up offers many opportunities to collect real-world data to help supplement clinical trials.This is the first study conducted through the CanSaRCC national collaboration of 11 sites across Canada permitting the unique opportunity to increase the sample size of patients with rare bone sarcomas receiving TKIs as a therapeutic intervention.In this regard, institutions were permitted to offer imaging evaluations at their own discretion and provided their own assessment of response and toxicity to drug.Therefore, our description of PFS is made within these limitations.We also did not collect details on disease burden prior to starting therapy and thus could not comment on whether TKI slowed the pace of disease progression.Furthermore, despite this national effort, the rarity of relapsed and refractory bone tumours precluded our ability to identify any patient factors that may predict response to TKI.Other limitations to this study include: (1) lack of information on the timing of when dose reductions occurred (first course or later), (2) no information on need for additional medications to treat side effects of TKIs and (3) the absence of information on whether the use of the TKI contributed to the ability to perform local control.Despite these limitations, further exploration of tumour biomarkers predicting response to anti-angiogenic therapy in bone tumours is of utmost interest for future projects.
In summary, we demonstrate meaningful real-world outcomes using TKI in children, adolescents and adults with relapsed/refractory bone tumours.Future trials should consider including TKIs as maintenance treatment.More national and international joint collaborations through sarcoma-oriented databases such as CanSaRCC will help to share precise data and facilitate interdisciplinary clinical and translational research in sarcoma.

2 F I G U R E 3
Swimmer plots and tumour response for patients treated either with regorafenib (pink bar) or with cabozantinib (light blue bar).(A) Osteosarcoma (n = 39), (B) Ewing's sarcoma (n = 18) and (C) chondrosarcoma (n = 9, ECMS-five out of nine).Bars ending with an arrow signify patients who are alive and continued response to TKI.A black square along the y-axis signifies patients who are deceased.The x-axis begins when the patient starts TKI and ends with patient's last follow-up.Response start date, denoted by triangle, is the date of best response assessment.The response and date denoted by a circle is the date of treatment end.PD (progression disease); SD (stable disease); CR (complete response) can be identified within each bar and are denoted by blue, red, green and dark brown lines, respectively.For patients whose best response is PD, the response start and end date overlap.Swimmer plots of TKI duration, line of therapy (LOT) and tumour progression of children versus adults diagnosed with osteosarcoma (A), Ewing sarcoma(B), chondrosarcoma or ECMS (C).(A,B,C-right plot) -The x-axis begins when the patient starts TKI and ends on last day the patient received TKI (denoted by circle).LOT = 1, LOT = 2 and LOT >2 can be identified within each bar and are denoted by blue, red and green, respectively.(A,B,C-Left Plot) -The x-axis begins when the patient was diagnosed with bone tumour and ends on last follow-up.Children (Age ≤ 18) and adults (Age ≥ 18) are denoted by yellow and grey lines, respectively.TKI start can be identified by triangle and denoted by blue (LOT = 1), red (LOT = 2) and green (LOT >2).