Enhanced expression of chromosome fragile site 10q25 in chronic myelogenous leukemia

Spontaneous expression of a BrdU-sensitive fragile site at 10q25 was observed in normal lymphocytes and malignant blood and bone marrow cells in chronic myelogenous leukemia (CML). The cells were marked by a Philadelphia chromosome rearrangement due to insertion of 22q11----q13 at 11q13. The fragile site at 10q25 was expressed in larger proportions of malignant than normal cells. Although this fragile site is not at a cancer chromosome breakpoint, malignancy enhanced its expression, consistent with a cascade effect.