IMPORTANCE The risk of extraocular extension from injecting chemotherapy into eyes with retinoblastoma is minimally understood; however, understanding this risk is important because of the increasing use of intravitreous chemotherapy. OBJECTIVE To evaluate the risk of extraocular extension in eyes with retinoblastoma that have received intravitreous chemotherapy injections. DESIGN, SETTING, AND PARTICIPANTS This retrospective cohort studywas performed in 655 patients at 10 retinoblastoma centers in North and South American, European, Israeli, and Chinese centers. Physicians at the retinoblastoma centers administered more than 120 intravitreous chemotherapy injections in eyes with retinoblastoma from February 1, 1999, through February 28, 2017. MAIN OUTCOMES AND MEASURES Risk of extraocular extension with secondary observational variables, including injection and precautionary techniques. RESULTS A total of 3553 intravitreous chemotherapy injections (3201 melphalan hydrochloride, 335 topotecan hydrochloride, and 17 methotrexate sodium) were administered to 704 eyes in 655 patients with retinoblastoma (mean [SD] age of patients at the time of the initial injections, 31.6 [11.6] months; 348 male [53.1%]). There were no extraocular tumor events related to prior intravitreous injections. This finding resulted in a calculated proportion of zero extraocular events per eye. According to the rule of 3, the risk is no greater than 0.08%injections. All 10 centers included in this study used at least 2 presumed precautionary injection methods (lowering of intraocular pressure, cryotherapy, ocular surface irrigation, ultrasonic biomicroscopy surveillance of the injection site, and subconjunctival chemotherapy deposition). CONCLUSIONS AND RELEVANCE With use of at least 2 presumed precautionary safety methods, no extraocular extension of tumor events occurred. According to the rule of 3, this finding suggests that the risk is no greater than 0.08%injections.
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