Benjamin King, Matthew W Wilson, Rachel C Brennan; Chemoreduction with Topotecan and Vincristine: Clinical Validation of a Novel Chemotherapeutic Regimen for Bilateral Intraocular Retinoblastoma. Invest. Ophthalmol. Vis. Sci. 2018;59(9):5982.
Purpose : To quantify retinoblastoma tumor response following two cycles of intravenous topotecan and vincristine (VT).
Methods : Retrospective non-comparative case series of 27 patients treated on the stratum B arm of the RET5 protocol, a phase II clinical trial for advanced bilateral retinoblastoma conducted at St. Jude Children’s Research Hospital (NCT00186888). Patients underwent high-resolution ophthalmic magnetic resonance imaging and ultrasound at diagnosis and following two cycles of systemic chemotherapy with VT. Focal consolidation therapy was withheld until completion of the second cycle. Tumor height and basal diameter were measured before and after treatment and tumor volumes were calculated.
Results : The required imaging at both time points was completed for 75 tumors in 43 eyes (23 patients). After two cycles of VT, median decrease in tumor height was 47% and median decrease in tumor diameter was 22%. Of 9 eyes with vitreous seeding, 8 demonstrated at least partial calcification with 4 showing complete regression. Overall, 61 of 75 tumors demonstrated >50% reduction in tumor volume. Univariate linear regression showed a significant correlation between percent decrease in tumor volume with increasing pre-treatment diameter (p<0.001) and proximity to optic nerve (p<0.001). Multivariate analysis revealed pre-treatment diameter to be the only significant predictor of tumor response (p=0.006).
Conclusions : Chemoreduction was achieved in the majority of retinoblastoma tumors following two cycles of VT. Overall response to therapy was comparable to that previously reported with the current standard chemotherapy regimen consisting of vincristine, etoposide and carboplatin. Tumor diameter was the most robust predictor of treatment response.