Trisomy 12 and structural abnormalities of 13q14 occurring in the same clone in chronic lymphocytic leukaemia.

Trisomy 12 and deletions or translocations of 13q14 are the commonest cytogenetic abnormalities in chronic lymphocytic leukaemia but rarely co-exist in the same patient. We describe eight patients from a series of > 400 patients with CLL in whom trisomy 12 and t or del 13 occur in the same clone. Using FISH we have identified clones with trisomy 12 alone, t or del 13q14 alone and both abnormalities, in each of the patients studied. This implies that neither trisomy 12 nor t or del 13q14 is the initiating event in leukaemogenesis, but does not exclude the possibility of a submicroscopic abnormality of 13q14 occurring as an early event.