CTNI-03. DECREASED GROWTH VELOCITY IN A PHASE 1 TRIAL (PNOC014) OF TOVORAFENIB IN PATIENTS WITH RECURRENT OR PROGRESSIVE MAPK-ALTERED TUMORS

Abstract BACKGROUND The mechanisms by which MAPK-targeted agents affect children in active phases of neurocognitive and physical development are poorly understood and hence, may place them at risk, particularly for uncommon patient toxicities that may require longer monitoring or larger patient cohorts to understand the long-term implications. Decreased growth velocity was identified in our investigator-initiated phase 1 trial (NCT03429803) of tovorafenib in relapsed MAPK-altered tumors. METHODS Forty-four patients enrolled from February 2018-October 2021. Toxicity was assessed according to CTCAE version 5 term growth suppression (GS). Patients were also evaluated retrospectively based on age-specific growth velocity norms. Post-pubertal patients (n=14), those with pre-existing growth abnormalities (n=3), and those on drug less than 6 months (n=10) were excluded (total n=27; 61%). Growth velocities for each patient were calculated prior to, on, and after discontinuing treatment as available. RESULTS Our safety database included 17 reported events of GS. Sixteen patients experienced grade 3 GS, defined as growth velocity reduction ≥50% ideally measured over a year compared to baseline. One patient experienced grade 2 GS, defined as reduced growth velocity by 30-49% compared to baseline. Separate retrospective analysis using age-specific growth velocity norms further confirmed that all 17 patients (100%) demonstrated decreased growth velocity compared to age-specific norms following start of treatment regardless of dose (3, 5 and 9 patients at 280, 420 and 530 mg/m2/dose, respectively with a mean dose of 507 mg, range: 220-840 mg). Four of 9 patients on 530 mg/m2 were dose reduced for other reasons and hence treated at 420 mg/m2. In 14/15 patients off drug, growth rates recovered at near normal or normal rates within 12 months of discontinuation. CONCLUSIONS Patients on tovorafenib experience decreased growth velocity, which is recoverable off drug. Long-term monitoring of growth and further preclinical investigations to mitigate this toxicity and understand its effect are warranted.