LAUSR

Abstract BACKGROUND Trametinib (Tr) has been applied in the treatment of children with various tumor types, often for prolonged periods. Little is known regarding immune function (IF) following prolonged Tr in this age group. OBJECTIVE Describe laboratory measures of IF in children on Tr. METHOD Patients receiving Tr had low grade glioma with BRAF anomalies (6), or neurofibromatosis-1 (16) with glioma or plexiform neurofibroma. IF was evaluated using leukocyte/lymphocyte counts, immunoglobulin levels, and antibody titres. RESULTS 22 patients received Tr. 2 also received Dabrafenib. Median age at Tr initiation of Tr was 7.75 years. As of June 2020, 7 patients have had IFT; results are pending on 15. Median duration of Tr therapy at time of IF was 3.5 years (0.8 – 4). In these 7 patients, median white cell count was 6.9 x 10^9/L (4.1 – 12.6), neutrophils 4.2 x 10^9/L (1.8 – 6.8) and lymphocytes 3.2 x 10^9/L (1.4 – 7). IgG levels, B cells and CD8 cytotoxic T cells were normal across 7/7 patients:medians 9.47 g/L (8.62 – 17), 0.51 x 10^9/L (0.2 – 1.26) and 0.58 x 10^9/L (0.25 – 2.03) respectively. CD3 and CD4 T cells: median 2.08 x 10^9/L (0.67 – 4.62) and 1.34 x 10^9/L (0.35 – 2.31), borderline low in 1 heavily pre-treated patient. An adequate immune response was present in all 4 vaccine antigens tested in 5/5 patients. CONCLUSION IF appears relatively intact, relevant for immunisation and infection precautions in children on Tr. Data on the complete cohort will be presented.