Hi Michele,
I did a little research and came up with the following.
Trysomy 8 has apparently no prognostic significance in CML although it may arise after interferon and/or imatinib treatment. It's significance is unknown.
It is found in other chronic myeloproliferative diseases polycytemia vera (PV) and idiopathic myelofibrosis but not found in essential thrombocythemia.
It is also found in 10% of myelofibrosis cases with chromosome anomalies, sometimes with +9.
There does not seem to be a prognostic significance.
I remember that a few people have had T8 with CML over the years with no apparent adverse long term effect In responses to imatinib.
Hope this helps...
Sandy