168
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.
 2 patients with polycythaemia vera (PV): Subject; 2: Subject.Population; chlorambucil: Treatment; polycythaemia vera (PV): Treatment.Disorder; chlorambucil: Treatment.Drug
Given event type and trigger, please tell me the arguments of all the listed option. Output format is "name1: role1; name2: role2". 
Event type: potential therapeutic event 
  Option: Treatment.Freq, Subject.Population, Combination.Drug, Subject.Gender, Treatment.Duration, Subject, Effect, Treatment, Treatment.Disorder, Treatment.Time_elapsed, Subject.Disorder, Subject.Race, Treatment.Route, Treatment.Dosage, Subject.Age, Treatment.Drug 
Text: {0} 
Answer:
 2 patients with polycythaemia vera (PV): Subject; 2: Subject.Population; chlorambucil: Treatment; polycythaemia vera (PV): Treatment.Disorder; chlorambucil: Treatment.Drug