Chromosomal mosaicism associated with prolonged remission in chronic myelogenous leukemia

The nature of the relationship between normal stem cells and the leukemic cells of chronic myelogenous leukemia (CML) is of considerable theoretical and practical importance. We studied a patient with CML who has maintained a complete hematologic remission for eight years without therapy. Presently, the only documentable abnormality is mosaicism for the Philadelphia (Ph1) chromosome. Studies of his bone marrow in vitro revealed normal colony formation in agar and normal cellular proliferation and differentiation in liquid culture. Observations in this patient indicate that a Ph1-positive clone may coexist with normal stem cells during prolonged remission in CML and the Ph1-positive cells may not always have a growth advantage over normal cells. The culture studies further suggest that the diminished proliferative capacity of the leukemic cells was not due to in vivo host suppressive factors.