This is a very rare case of CML developing a granulocytic sarcoma, that is an equivalent of a blast crisis, when the patient was in optimal response. I have never seen such a case in more than 40 years.
The pathologic material of the granulocytic sarcoma should be still available, to investigate if the sarcoma cells were Ph+ BCR-ABL+, and in that case if there was a BCR-ABL mutations.
If the pathologic material was analysed or can be analysed, and was Ph neg, BCR-ABL neg, I would suggest to continue the TKI, and to monitor very closely.
If the pathologic material was analysed or can be analysed, and was Ph+ BCR-ABL+, I would suggest to go to transplant. The risk of developing resistance would be very high.
If the pathologic material was not analysed and cannot be analysed, I would suggest to go to transplant as well, because morphology would not prove but would suggest that the granulocytic sarcoma was also Ph+ and BCR-ABL+.
Please, let me know the development.