I would continue TKI at full dose. I have now done this with chemotherapy in a couple of dozen cases and only in one case of bladder cancer, did the drug have to stop. Remember, it should be active only against CML clones, not the normal clones in a patient who has been on it for a while and thus is not likely going to have an impact on the normal stem cells which will be affected by the chemo. Unless there is a potential interaction between the chemo and the TKI you should be fine.
Check for all the reasons for loss of TKI response. If a switch is necessary, you could make a theoretical argument about using dasatinib because of the src activity which may have some impact on the breast cancer as well.