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In a randomized, open-label phase 3 study of 61 children aged 1-12 years old with X-linked hypophosphatemia (XLH) previously treated with conventional therapy, changing to burosumab every 2 weeks (Q2W) for 64 weeks improved the phosphate metabolism, radiographic rickets, and growth compared with conventional therapy. In this open-label extension period (weeks 64-88), 21 children continued burosumab Q2W at the previous dose or crossed over from conventional therapy to burosumab starting at 0.8 mg/kg Q2W with continued clinical radiographic assessments through week 88. Efficacy endpoints and safety observations were summarized descriptively for both groups (burosumab continuation, n = 6; crossover, n = 15). At week 88 compared with baseline, improvements in the following outcomes were observed in the burosumab continuation and crossover groups, respectively: mean (SD) RGI-C rickets total score (primary outcome), +2.11 (0.27) and +1.89 (0.35); mean (SD) RGI-C lower limb deformity score, +1.61 (0.91) and +0.73 (0.82); and mean (SD) height Z-score + 0.41 (0.50) and +0.08 (0.34). Phosphate metabolism normalized rapidly in the crossover group and persisted in the continuation group. Mean (SD) serum alkaline phosphatase decreased from 169% (43%) of the upper limit of normal (ULN) at baseline to 126% (51%) at week 88 in the continuation group and from 157% (33%) of the ULN at baseline to 111% (23%) at week 88 in the crossover group. During the extension period, treatment-emergent adverse events (AEs) were reported in all 6 children in the burosumab continuation group and 14/15 children in the crossover group. The AE profiles in the randomized and extension periods were similar, with no new safety signals identified. Improvements from baseline in radiographic rickets continued in the extension period among children with XLH who remained on burosumab. Children who crossed over from conventional therapy to burosumab demonstrated a rapid improvement in phosphate metabolism and i, This study was sponsored and funded by Ultragenyx Pharmaceutical Inc. in partnership with Kyowa Kirin International plc. Medical writing support was provided by Ben Scott, PhD (Scott Medical Communications, LLC) and was funded by Ultragenyx Pharmaceutical Inc. Additional editorial support was provided by Jamie Ziobro, an employee and share holder of Ultragenyx Pharmaceutical Inc. At Indiana University, the research was done at the Indiana Clinical and Translational Sciences Institute, funded in part by UL1TR002529 from the National Institutes of Health, National Center for Advancing Translational Sciences, Clinical, and Translational Sciences Award. In Montreal and St. Louis, the work was also supported by the Shriners of North America. Dr. Ward is supported by a Tier 1 (Senior) Research Chair in Pediatric Bone Disorders from the University of Ottawa and Children's Hospital of Eastern Ontario Research Institute.

PURPOSE: In an open label, randomized, controlled, phase 3 trial in 61 children 1 to 12 years old with X-linked hypophosphatemia (XLH), burosumab improved rickets versus continuing conventional therapy with active vitamin D and phosphate. Here, we conducted an analysis to determine whether skeletal responses differed when switching to burosumab versus continuing higher or lower doses of conventional therapy. METHODS: Conventional therapy dose groups were defined as: higher dose phosphate >40 mg/kg [HPi], lower dose phosphate ≤40 mg/kg [LPi], higher dose alfacalcidol >60 ng/kg or calcitriol >30 ng/kg [HD], and lower dose alfacalcidol ≤60 ng/kg or calcitriol ≤30 ng/kg [LD]. RESULTS: At Week 64, the Radiographic Global Impression of Change (RGI-C) for rickets was higher (better) in children randomized to burosumab versus conventional therapy for all pre-baseline dose groups: HPi (+1.72 versus +0.67), LPi (+2.14 versus +1.08), HD (+1.90 versus +0.94), LD (+2.11 versus +1.06). At Week 64, the RGI-C for rickets was also higher in children randomized to burosumab (+2.06) versus conventional therapy for all on-study dose groups: HPi (+1.03), LPi (+1.05), HD (+1.45), LD (+0.72). Serum alkaline phosphatase also decreased in the burosumab treated patients more than in the conventional therapy group, regardless of on-study phosphate and active vitamin D doses. MAIN CONCLUSIONS: Prior phosphate or active vitamin D doses did not influence treatment response after switching to burosumab among children with XLH and active radiographic rickets. Switching from conventional therapy to burosumab improved rickets and serum alkaline phosphatase more than continuing either higher or lower doses of phosphate or active vitamin D.

CONTEXT: Younger age at treatment-onset with conventional therapy (Pi/D) is associated with improved growth and skeletal outcomes in children with X-linked hypophosphatemia (XLH). The impact of age on burosumab efficacy and safety in XLH is unknown. OBJECTIVE: Explore the efficacy and safety of burosumab versus Pi/D in younger (<5 years) and older (5 to 12 years) children with XLH. DESIGN: Post-hoc analysis of 64-week, open-label, randomized controlled study. SETTING: Sixteen academic centers. PATIENTS OR OTHER PARTICIPANTS: Sixty-one children 1-12 years of age with XLH (younger, n=26; older, n=35). INTERVENTIONS: Children received burosumab starting at 0.8 mg/kg every 2 weeks (younger, n=14; older, n=15) or continued Pi/D individually titrated per recommended guidelines (younger, n=12; older, n=20). MAIN OUTCOME MEASURE: Least squares means difference (LSMD) in Radiographic Global Impression of Change (RGI-C) rickets total score from baseline to week 64. RESULTS: The LSMD in outcomes through 64 weeks on burosumab versus conventional therapy by age group were as follows: RGI-C rickets total score (younger, +0.90; older, +1.07), total rickets severity score (younger, -0.86; older, -1.44), RGI-C lower limb deformity score (younger, +1.02; older, +0.91), recumbent length or standing height Z-score (younger, +0.20; older, +0.09), and serum alkaline phosphatase (younger, -31.15% of upper normal limit [ULN]; older, -52.11% of ULN). On burosumab, dental abscesses were not reported in younger children but were in 53% of older children. CONCLUSIONS: Burosumab appears to improve outcomes in both younger and older children with XLH, including rickets, lower limb deformities, growth, and alkaline phosphatase, compared with Pi/D., Funding agencies:Ultragenyx Pharmaceutical Inc.Kyowa Kirin International plcUniversity of Ottawa Clinical Research Chair Program

In a randomized open-label phase 3 trial in 62 children (1–12 years) with X-linked hypophosphatemia (XLH) (NCT 02915705), switching from conventional therapy (oral phosphate plus active vitamin D) to burosumab, a monoclonal antibody targeting fibroblast growth factor 23, significantly improved serum phosphate concentration, rickets, lower-extremity deformities, growth, mobility, and patient-reported outcomes (PROs) at 64 weeks. Children in Europe, USA, Canada, and Australia who completed 64 weeks’ treatment could continue to receive burosumab in the extension period (burosumab continuation group) or cross over from conventional therapy to burosumab (crossover group) to 124 weeks. A Patient-Reported Outcomes Measurement Information System (PROMIS) questionnaire was used in children aged ≥5 years to measure Pain Interference, Physical Function Mobility, and Fatigue; health-related quality of life was measured using the SF-10 Health Survey for Children (n=35). Here, we describe changes in PROs from baseline to weeks 64 and 88, and report whether the 3-point minimal important difference (MID) was reached for PROMIS domains (Thissen et al., 2016; PMID 26118768). The mean change from baseline exceeded the MID for Pain Interference at weeks 64 and 88 and for Fatigue at week 64 in the burosumab continuation group, and for Pain Interference and Fatigue at week 88 in the crossover group. Similar improvements in SF-10 Physical Health were seen baseline to week 64 in the burosumab continuation group, and week 64 to 88 in the cross-over group. SF-10 Psychosocial Health changed little in either group at the two timepoints. Treatment with burosumab improved Pain Interference and Fatigue beyond the MID in children with XLH who switched from conventional therapy to receive 24 weeks of burosumab. Improvements were also maintained in children who received an additional 24 weeks’ burosumab treatment.

Childhood, adolescent, and young adult cancer survivors are at increased risk of reduced bone mineral density. Clinical practice surveillance guidelines are important for timely diagnosis and treatment of these survivors, which could improve bone mineral density parameters and prevent fragility fractures. Discordances across current late effects guidelines necessitated international harmonisation of recommendations for bone mineral density surveillance. The International Late Effects of Childhood Cancer Guideline Harmonization Group therefore established a panel of 36 experts from ten countries, representing a range of relevant medical specialties. The evidence of risk factors for very low and low bone mineral density and fractures, surveillance modality, timing of bone mineral density surveillance, and treatment of very low and low bone mineral density were evaluated and critically appraised, and harmonised recommendations for childhood, adolescent, and young adult cancer survivors were formulated. We graded the recommendations based on the quality of evidence and balance between potential benefits and harms. Bone mineral density surveillance is recommended for survivors treated with cranial or craniospinal radiotherapy and is reasonable for survivors treated with total body irradiation. Due to insufficient evidence, no recommendation can be formulated for or against bone mineral density surveillance for survivors treated with corticosteroids. This surveillance decision should be made by the survivor and health-care provider together, after careful consideration of the potential harms and benefits and additional risk factors. We recommend to carry out bone mineral density surveillance using dualenergy x-ray absorptiometry at entry into long-term follow-up, and if normal (Z-score > -1), repeat when the survivor is aged 25 years. Between these measurements and thereafter, surveillance should be done as clinically indicated. These recommendations facilitate evidenc