Abstract
Chronic myelocytic leukemia is a disease in which biomedical research efforts have paid substantial dividends in recent years. Both laboratory and clinical investigators have found that this disease, first described as "splenic leukemia" over 100 years ago, contains some important lessons for the astute observer. An early, notable example of the value of careful laboratory observation was the demonstration of the Philadelphia (Ph1) chromosome in patients with this disease.1 subsequent cytogenetic analyses using banding techniques demonstrated that in most cases of chronic myelocytic leukemia, the Ph1 chromosome arises from a balanced translocation between the long arms of chromosomes 9 . . .