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Bone marrow chromosomes were studied in 2 patients with polycythaemia vera (PV) at the time of diagnosis and several times subsequently during therapy with chlorambucil.
 potential therapeutic event: therapy 
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:
 potential therapeutic event: therapy 