COPENHAGEN—Results of a large study suggest that stopping treatment with tyrosine kinase inhibitors (TKIs) can be safe for patients with chronic myeloid leukemia (CML) in deep molecular response (MR4).
Six months after patients stopped receiving a TKI, the relapse-free survival was 62%. At 12 months, it was 56%.
Havinga longer duration of TKI treatment and a longer duration of deep molecular response were both associated with a higher likelihood of relapse-free survival.
These results, from the EURO-SKI trial, were presented at the 21st Congress of the European Hematology Association (abstract S145*) by Johan Richter, MD, PhD, of Skåne University Hospital in Lund, Sweden.
The goal of the EURO-SKI study was to define prognostic markers to increase the proportion of patients in durable deep molecular response after stopping TKI treatment.
The trial included 760 adults with chronic phase CML who were on TKI treatment for at least 3 years. Patients were either on their first TKI or on their second TKI due to toxicity with their first. (None had failed TKI treatment.)
Patients had been in MR4 (BCR/ABL <0.01%) for at least a year, which was confirmed by 3 consecutive polymerase chain reaction (PCR) results during the last 12 months. The final MR4 confirmation was performed in a EUTOS standardized laboratory.
After the final MR4 confirmation, patients stopped TKI treatment. They underwent real-time quantitative PCR (RQ-PCR) every 4 weeks for the first 6 months and every 6 weeks for the next 6 months. In years 2 and 3, they underwent RQ-PCR every third month.
The patients had a median age at diagnosis of 52 (range, 11.2-85.5) and a median age at TKI stop of 60.3 (range, 19.5-89.9). The median duration of TKI therapy was 7.6 years (range, 3.0-14.2), and the median duration of MR4 before TKI stop was 4.7 years (range, 1.0-13.3).
Most patients had received imatinib (n=710) as first-line TKI treatment, though some received nilotinib (n=35) or dasatinib (n=14). The type of first-line TKI was unknown in 1 patient. Second-line TKI treatment included imatinib (n=7), nilotinib (n=47), and dasatinib (n=57).
Relapse, survival, and safety
Six months after stopping TKI treatment, the cumulative incidence of molecular relapse was 37%. It was 43% at 12 months, 47% at 24 months, and 50% at 36 months.
In all, 347 patients had a molecular relapse. Seventy-two patients had BCR/ABL >1%, and 11 lost their complete cytogenetic response. None of the patients progressed to accelerated phase or blast crisis.
Among patients who restarted TKI treatment, the median time to restart was 4.1 months. Fourteen patients restarted treatment without a loss of major molecular response.
Dr Richter noted that the study is still ongoing, but, thus far, more than 80% of patients who restarted TKI therapy have achieved MR4 again.
The molecular relapse-free survival was 62% at 6 months after TKI stop, 56% at 12 months, 52% at 24 months, and 49% at 36 months.
There were 9 on-trial deaths, none of which were related to CML. Five patients died while in remission.
Previous studies revealed a TKI withdrawal syndrome that consists of (mostly transient) musculoskeletal pain or discomfort. In this study, 30.9% of patients (n=235) reported musculoskeletal symptoms, 226 with grade 1-2 events and 9 with grade 3 events.
Prognostic factors
The researchers performed prognostic modeling in 448 patients who previously received imatinib. Univariate analysis revealed no significant association between molecular relapse-free survival at 6 months and age, gender, depth of molecular response, Sokal score, EURO score, EUTOS score, or ELTS score.
However, TKI treatment duration and MR4 duration were both significantly (P<0.001) associated with major molecular response status at 6 months.
The odds ratio for treatment duration was 1.16 (95% CI, 1.08-1.25), which means that an additional year of imatinib treatment increases a patient’s odds of staying in major molecular response at 6 months by 16%.
The odds ratio for MR4 duration was also 1.16 (95% CI, 1.076-1.253), which means that an additional year in MR4 before TKI stop increases a patient’s odds of staying in major molecular response at 6 months by 16%.
Dr Richter noted that treatment duration and MR4 duration were highly correlated, which prevented a significant multiple model including both variables. He said the researchers will conduct further analyses to overcome the correlation between the 2 variables and determine an optimal cutoff for MR4 duration.
The team also plans to collect more data on pretreatment with interferon, as there is reason to suspect it has an influence on major molecular response duration after TKI discontinuation.
*Data in the abstract differ from data presented at the meeting.