However, the cessation of TKI treatment is considered impossible, because in vitro assays show that CML stem cells cannot be eliminated [1]. Clinically, neither Complete Cytogenetic Remission (CCyR) nor a Major Molecular Response (MMR) is sufficient to prevent recurrence after the cessation of medication [2,3]. Furthermore, progression from chronic to acute-phase disease is considered a major risk factor for treatment cessation. Such a progression is difficult to treat with TKI alone; the European Leukemia Net (ELN) guidelines and the hematopoietic tumor guidelines of the Japanese Society of Hematology prohibit TKI treatment cessation in daily practice outside planned clinical research settings [4,5]. On the other hand, treatment effects are reported to be sometimes maintained after incidental or planned treatment cessation prompted by side effects or pregnancy [6-11].
Previous prospective imatinib cessation trials
The Stop Imatinib (STIM) prospective cessation trial was announced in 2010 by a French group led by Mahon [12]. The subjects were 100 patients with CML maintaining Complete Molecular Response (CMR) without the breakpoint cluster region-Abelson 1 (bcr-abl) mRNA detected by high-sensitivity quantitative Polymerase Chain Reaction (PCR) for over 2 years. Among them, 39% had long-term CMR after imatinib cessation.
In contrast, molecular genetic evidence of recurrence was found in 61% of patients within 6 months after imatinib cessation. However, re-administration of imatinib in patients with recurring disease resulted in a rapid molecular genetics effect without disease progression. Follow-up data were published by the
American Society of Hematology (ASH) annual meeting in 2013, but no new relapses or disease progressions were observed [13].
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