Multi-institutional study evaluating the role of liquid biopsy to determine risk of extraocular disease, therapy response and recurrence in retinoblastoma

BACKGROUND: We analyzed whether changes in RB1 circulating tumor DNA (ctDNA) variant allele frequency (VAF) in plasma and/or cerebrospinal fluid (CSF) was associated with clinical outcomes in patients with retinoblastoma (RB). METHODS: We reviewed all RB patients treated at MSKCC and SCEH who had serial plasma and CSF ctDNA analyses. RESULTS: 4/33 intraocular RB patients developed extraocular RB, all associated with an increase in plasma RB1 ctDNA VAF. In the remaining 29 patients who did not develop extraocular disease, RB1 ctDNA remained undetectable. Plasma RB1 ctDNA was positive in 15 of 16 extraocular RB patients at diagnosis and became undetectable in 13 of 14 patients post treatment; the sole patient with rising RB1 ctDNA died of disease. Two stage 4a patients who developed CNS relapse had positive/rising levels of plasma RB1 ctDNA VAF at relapse. 11 patients in remission have undetectable RB1 ctDNA. Two stage 4a patients with residual bony lesions post-chemotherapy but negative ctDNA remain in remission. CSF ctDNA was positive in all 7 patients with central nervous system (CNS) disease at diagnosis and became undetectable post treatment in 3 of 4 patients; the only patient with rising ctDNA died of disease. Two suffered disease recurrence in the CNS post treatment associated with positive/rising levels of CSF RB1 ctDNA VAF. Two stage 4a RB patients had CSF ctDNA positivity at initial diagnosis and recurred in the CNS. CONCLUSIONS: Longitudinal ctDNA may predict risk of developing extraocular RB. Its use for monitoring and risk stratification deserves further study.