2217
Seven of the eight cases of acute leukemia occurred in a series of 553 patients treated with Treosulfan for ovarian cancer in the period from 1970 to 1977 and followed closely for a total of 1159 patient-years up to February 1978.
 adverse event: occurred 
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: occurred 