Duration of Major Molecular Response and Discontinuation in Deep Molecular Response (MR4.5) Were Associated with Longer Treatment-Free Survival after Imatinib Discontinuation - Results from Two Prospective Brazilian Trials

Several trials have demonstrated the feasibility of discontinuation of tyrosine kinase inhibitors (TKI) treatment in chronic myeloid leukemia (CML) patients (pts) with deep molecular response. Aims: to report the results of two Brazilian imatinib (IM) discontinuation trials and to evaluate factors impacting in treatment-free remission (TFR) and treatment-free survival (TFS) after IM discontinuation. Methods:Between September 2016 and January 2019, 60 CML pts were included in two ongoing phase II, single arm, prospective Brazilian discontinuation trials: Pilot Study of Discontinuation in Patients With Chronic Myeloid Leukemia With Deep Molecular Response - Evaluation of Pioglitazone in Treatment-free Remission (TFR) (EDI-PIO UNICAMP)(NCT02852486)and Imatinib Discontinuation in Patients With Chronic Myeloid Leukemia Chronic Phase With Sustained MR4log(USP) (NCT03239886). Inclusion criteria: age >18 years, chronic phase, minimum of 3 years of IM therapy, deep molecular response for ≥ 2 years (confirmed by 4 tests in the last 2 years, defined as MR4.0 in USP trial and MR4.5 in EDI-PIO). Patients participating in EDI-PIO trial used pioglitazone 30 mg/day plus IM for 3 months before IM discontinuation (n=30). After discontinuation, pts were monitored by quantitative RQ-PCR monthly in the first year, every 2 months in the second year and every 3 months in the third year. Criteria for IM re-initiation: loss of MMR (in one test), loss of cytogenetic response, loss of hematologic response, disease progression or confirmed loss of MR4.0 (this criteria used only in EDI-PIO trial). TFR was calculated from the date of discontinuation until first event (loss of MMR; IM reintroduction; death any cause or last follow-up); TFS was calculated from the date of IM discontinuation until reintroduction or last follow-up (censoring deaths not related to CML). Adverse events after IM discontinuation were reported according to CTCAE. Results:Data cut-off for analysis was February 2019. In the 1stanalysis 48 pts who discontinued IM in MR4.5 were analyzed. Patient's characteristics from EDIPIO (n=30) and USP (n=18) trials were: 57% vs. 67% male, median age of 55 (29-77) and 56 (33-95) years (29-95) at discontinuation; 16% and 33% had used previously Interferon; median duration of IM treatment of 10 (3-16) vs. 10 (5-15) years; median duration of MMR 95 (30-149) vs. 93 (57-130) months; MR4.0 was 90 (26-135) vs. 89 (30-123) months; and MR4.5 was 76 (23-135) vs. 75 (30-102) months; none variable had statistical difference.One patient died in MMR due to cardiac failure. TFR was 61% (95% CI 47-75) at 20 months. Sixteen (33%) out 48 re-initiated IM (2 with confirmed loss of MR4.0 and 14 with loss of MMR) in a median time of 20 (1-26) months. All relapsed pts recovered MMR after IM reintroduction, in a median time of 2 months (0-4). There was no transformation to advanced phases. No serious adverse events were reported during pioglitazone treatment. In the Cox regression the duration of MMR was associated with a longer TFR HR: 0.96 (beta-) (CI 95%:0.94-0.99, P= 0.006). Gender, age at diagnosis, age at discontinuation, treatment with pioglitazone, Sokal and EUTOS scores, BCR-ABL transcripts type, duration of IM therapy, duration of MR4.0 and MR4.5 and previous use of Interferon did not affect TFR.In the second analysis all 60 pts were included. TFS was 56% and was higher in pts who discontinued IM in sustained MR4.5 vs. MR4.0 (63% vs. 33%, P=0.04)(Figure). The independent factors for TFR in the multivariate analysis by Cox-regression were the duration of MMR [HR: 0.97 (beta-), 95%CI: 0.95-0.98, P=0.001] and intermediate/high risk Sokal [HR 3.14 95%CI: 1.08-9.11, P= 0.035]. Twenty-four out of 60 pts (40%) re-initiated IM (2 with confirmed loss of MR4.0 and 22 with loss of MMR).Adverse events occurred in 38 (63%) pts, 30% attributed to withdrawal syndrome. Some pts presented more than one event. Grade 1-2: arthralgia or muscular pain (17), hyperglycemia (4), hypertriglyceridemia (2), polycythemia (2), hypertension (3), and others (11). Four pts had grade 3-4 event: arthralgia (1), death for cardiac failure (1), abortion and hypertriglyceridemia (1). Conclusions:both trials demonstrated the feasibility and safety of IM discontinuation in pts in sustained deep molecular response. The duration of MMR was associated with a higher TFR and TFS rate. Imatinib discontinuation was more successful in pts in stable MR4.5. Figure Disclosures Pagnano: Pint Pharma: Consultancy; Abbvie: Consultancy; Sandoz: Consultancy. Delamain:Novartis: Honoraria.