Imatinib mesylate was the first inhibitor of Abl tyrosine kinase used for the treatment of Chronic Myeloid Leukemia. Before tyrosine kinase inhibitors, most patients died within four years after diagnosis of the disease, since the only form of survival offered was bone marrow transplantation, a procedure not accessible to everyone. We report a real-life case of the first patient with Chronic Myeloid Leukemia to receive imatinib mesylate in Amazonas and achieve treatment-free remission.

36 years old, male, only child, diagnosed in 1998 with Chronic Myeloid Leukemia, Philadelphia chromosome positive, in the chronic phase. He presented with mild anemia, 159.000 leukocytes, staged deviation to blasts and PC: 278,000/mm3. Sokal index 0.7 points, low risk, hypercellular BM without blast infiltration, positive cytogenetics t (9;22) (q34; q11), receiving cytoreduction with hydroxyurea. The patient evolved with normalization of blood count without clinical symptoms but persisted with positive cytogenetics. HLA-compatibility test in 12 thousand donors found no donor. We requested patient entry a phase III clinical trial of imatinib, in MD Anderson Hospital, in the United States, but the study was closed, and it was recommended to use the protocol Interferon 9,000iu/day, SC week + Ara-C 10 mg SC day, from November 2018 to October 2020. But the patient suffered many side effects, such as muscle pain and diarrhoea, with several interruptions due to severe cytopenia’s followed by leucocytosis and suspected progression to an aggressive phase. In Novembre 2020, the patient was included in a new study in MD Anderson Hospital, performing positive cytogenetics and positive PCR with b2a2 and b3a2 transcripts and starting imatinib 600 mg/day, achieving hematologic remission, followed by cytogenetics and molecular remission. After 5 years, imatinib was reduced to 400 mg/day. He maintained periodic molecular control and in 2018, with PCR still undetected, imatinib was discontinued. For the next seven years PCR remained negative, implying remission without treatment.

Approximately 40-50% of patients who used imatinib and discontinued treatment remained in complete molecular remission. The Sokal index, when low risk, favors deep remission and increases the possibility of discontinuation by 81%, as was the case of the patient reported. The concept of remission without treatment still requires further studies, since the molecular mechanisms that regulate discontinuation are not clearly known.