Imatinib Suspension and Validation (ISAV) Study: Final Results at 79 Months

Introduction. It is known that imatinib can be safely discontinued in patients (pts) with Chronic Myeloid Leukemia (CML) with minimal residual disease. Here we report an update of the Imatinib Suspension And Validation (ISAV) study at 79 months (mts) from study initiation to provide long term follow up data.

Aims. The ISAV study aims to validate the capability of digital PCR (dPCR) to predict relapses after imatinib discontinuation in CML pts with negative Q-RT-PCR and to evaluate relapse rate, time to recurrence, survival and the impact of imatinib treatment on Quality of Life (QoL).

Methods. This study involves 15 sites, 10 in Italy and 1 in each of the following countries: Germany, Spain, The Netherlands, Canada and Israel. CML pts (chronic or accelerated phase) treated with imatinib for more than 2 years and in complete molecular remission (CMR) were eligible. Patients had to be in CMR for at least 18 mts, with a minimum of 3 Q-RT-PCR performed at their own sites. After discontinuation of imatinib therapy, Q-RT-PCR was performed monthly (mts 1-6), bimonthly for 36 mts and then every 6 mts for additional 2 years, to assess the maintenance of the molecular remission. The loss of molecular remission was defined as two consecutive positive Q-RT-PCR tests with at least one BCR-ABL/ABL value above 0.1%. Patients losing molecular remission resumed imatinib treatment at the same dosage used before interruption. dPCR was performed at screening and at 36 mts for those pts who were still in remission. Patients' QoL during imatinib discontinuation/resumption was evaluated through the EORTC QLQ-C30 questionnaire.

Results. The ISAV study enrolled 112 pts with a median follow-up time of 60.0 mts [95% CI: 59.6-60.6] for pts who do not relapsed; 66.1% of them completed the study as per protocol. The 58.9% of pts were male and 37.4% were aged 65 or older; median duration of imatinib treatment was 103.2 mts with median duration of CMR of 25.6 mts before imatinib discontinuation. At 79 mts from imatinib discontinuation, 56 pts of the 107 eligible ones relapsed and resumed imatinib with a relapse rate of 52.3% [95%CI: 20.4-32.6]; 69.6% of them relapsed in the first 9 mts. Of the 52 not-relapsed pts, 40 (76.9%) regained Q-RT-PCR positivity without losing MMR. In this latter group 2 pts experienced late relapses, at 30.6 and 45.5 mts respectively. A loss of CCyR occurred in 13 pts (23.6%): 10/13 CCyR losses were recovered, the remaining 3 were not assessed for response. No case of CML progression or resistance to imatinib was observed. After the resumption of imatinib the median time to MMR/CMR was 1.8 [95% CI: 1.0-2.0] mts. No significant correlation between relapse and previous duration of imatinib treatment, use of interferon, time to CCyR, Sokal score or duration of CMR was identified, while an inverse relationship between pts age and risk of relapse was evident. dPCR results before imatinib discontinuation showed that 23.4% of pts were positive and 76.6% negative at the time of discontinuation, with a Negative Predictive Value ratio (dPCR/Q-RT-PCR) of 1.1 [95%CI: 0.99-1.22]. At 36 mts from imatinib discontinuation 80.4% [95%CI: 30.6-50.4] of the pts tested were positive in dPCR. Moreover, the results of dPCR performed at imatinib discontinuation and age together can predict the risk of relapse: pts with less than 45 years and with a positive dPCR had the highest risk of relapse (100%) as opposed to pts ≥45 years and with negative dPCR (36.1%). The analysis of QoL evidenced a statistically significant improvement in the general well-being and symptoms scales at 1 month after imatinib discontinuation, particularly with regard to nausea, diarrhea, fatigue and insomnia (p<0.05). An inverse and transient trend toward increased pain emerged at mts 1 and 3.

Conclusions. At 79 mts from the beginning of the study, 52.3% of pts relapsed, with 24% loosing CCyR. The majority of relapses occurred in the first 9 mts after discontinuation however late relapses were also observed, up to the 4th year. Therefore, pts who discontinue imatinib should be monitored for a long period of time, especially if they show positive PCR values after discontinuation. All relapsed pts including those who lost CCyR regained their original response after restarting TKI. Age <45 years and dPCR positivity are significantly associated with relapses. QoL analysis showed a significant decrease in symptoms after imatinib discontinuation. Funded by Regione Lombardia.