659
We report the case histories of identical twin brothers who developed concordant acute lymphoblastic leukemia at the age of 4 years and who later developed leukoencephalopathy and hydrocephalus related to central nervous system prophylaxis by, in the first case intrathecally administered methotrexate and, in the second by intrathecally administered methotrexate and cranial irradiation.
 adverse event: developed 
Please tell me event type and its trigger word from given type options. Output format is "type: trigger".  Option: adverse event, potential therapeutic event 
Text: {0} 
Answer:
 adverse event: developed 