Etude Observationnelle Biologique Sur le Syndrome de Sevrage Des Inhibiteurs de Tyrosine Kinase Dans la Leucémie Myéloïde Chronique.

The success of TKI in the treatment of chronic myeloid leukemia is undeniable. Indeed, since the advent of imatinib in 2000 and the subsequent 4 other TKIs, this once fatal disease has become just another chronic disease with patient life expectancy close to the general population. Lifelong TKI therapy offers an 'operational cure' which means quiescent BCR-ABL leukemic stem cells are not eradicated but only controlled.

This statement was challenged in 2008 by the French 'STIM' study in which patients with undetectable BCR-ABL were proposed to discontinue their imatinib: 40% of these patients successfully achieved treatment free remission (TFR) with no recurrence of the disease. These figures are confirmed by the Australian 'TWISTER' study. The resumption of Imatinib therapy was triggered by the positivity of BCR-ABL. In the A-STIM study, the loss of major molecular response is the main criteria to resume imatinib. Accordingly, TFR was a success in 60% of patients. Similar figures was published with second generation TKIs with the same criteria.

In the light of these studies, it is clear that the fields have moved to a more ambitious goal than the operational cure, without the need for remaining on TKI.

Paradoxically, a new syndrome emerged from the Sweden group in 2014: 'the TKI withdrawal syndrome. It consisted of musculoskeletal pains resembling the Polymyalgia Rheumatica in CML patients after discontinuation of Imatinib. It occurred within 6 weeks in 30% of the patients who went on stopping imatinib. Patients with severe pain responded to 10-20 mg of prednisolone. Similar manifestations were described in the European 'EuroSki' study. No explanation was found.

It is well known that TKIs have off-target effects. In addition to BCR-ABL, they inhibit c-Kit, SRC, PDGFR, BTK, TEC, NFKB pathways resulting in anti-inflammatory effects. They can also cause disturbances in electrolyte balance (hypophosphatemia) and bone metabolism. Some research teams have correlated the success of TFR to the increase in cytotoxic NK cells and production IFN and TNFα.