Low-level Bcr-Abl mutations are very rare in chronic myeloid leukemia patients who are in major molecular response on first-line nilotinib

We investigated whether low-level Bcr-Abl kinase domain mutations can be detected in patients who have stable responses to first-line nilotinib-like it is known to happen in patients receiving imatinib. We screened for mutations twelve such patients by cloning and sequencing. Only one case was found to harbor mutations at low levels (including a T315I). However, major molecular response (MMR) was maintained and it even improved to complete molecular response. Our results suggest that a) Bcr-Abl mutations, even at low level, seem to be very rare in patients in MMR on first-line nilotinib; b) low-level mutations do not always predict for subsequent relapse.