Outcome After Failure to Second Generation Thyrosine Kinase Inhibitors(TKI) Treatment as Frontline Therapy for Patients with Chronic Myeloid Leukemia (CML) In Chronic Phase(CP).

Imatinib has been the standard frontline therapy for patients with CML in early CP. 2^nd generation TKIs (nilotinib, dasatinib) have been reported to be more effective than imatinib as frontline therapy in rates of response and transformation. Nilotinib has received regulatory approval for this indication and others (dasatinib, bosutinib) may come soon. Although fewer patients are expected to experience failure to therapy with the use of these agents, these patients will represent a management challenge. The characteristics, management and outcome of patients who fail therapy with 2^nd generation TKI used as initial therapy has not been reported.

To analyze the characteristics of patients who fail therapy with 2^nd generation TKI used as initial therapy, their management, and outcome after failure to initial therapy.

Two parallel studies of 2^nd generation TKI as initial therapy for CML early CP are being conducted at MDACC, one with nilotinib and one with dasatinib. The study with nilotinib includes also patients in accelerated phase (AP) that have received no other prior therapy. The records of all patients who were taken off therapy from these trials were reviewed to investigate the reasons for failure, subsequent management and outcome.

A total of 172 pts have been treated with dasatinib (n=82) or nilotinib (n=90; 9 in AP) since 2005. After a median follow-up of 18.9 months, 23 pts (14%) have discontinued therapy: 13 (16%) pts in the nilotinib study (2 of them treated in AP), and 10 (12%) in the dasatinib study. Their median age 48 years (range:19–73) and they had received therapy with nilotinib or dasatinib for a median of 5.2 (0.03-48) months. Reasons for nilotinib treatment discontinuation include: toxicity 4 pts (elevated lipase, acute pancreatitis + atrial fibrillation, pericardial effusion and acute renal failure, one each), transformation to blast phase (BP) 3 pts (2 of them treated in AP), and other reasons 6 pts (2 each for insurance issues, patient request and non-compliance). Reasons for discontinuation of dasatinib include: toxicity 5 pts (2 pleural effusion, 1 prolonged thrombocytopenia, 1 bone pain, 1 congestive heart failure), 2 pts for loss of response, and 3 pts for pts' choice. Best response to frontline treatment with nilotinib or dasatinib was 6 (26%) pts major molecular response, 6 (26%) pts complete cytogenetic response, 1 (4%) pt partial cytogenetic response, 3 (13%) pts minor cytogenetic response, 1 (4%) pt with no response and 6 (26%) pts nonevaluable. At the time of failure 18 pts were in CP, 4 pts in BP (one pt transformed shortly after discontinuation) and 1 AP. At the time of treatment interruption, 14 pts had BCR-ABL sequencing and 2 were found to have mutations (F359C, Y253H); 3 pts had new additional chromosomal abnormalities (ie, clonal evolution). Subsequent treatment after failure to initial therapy include: imatinib in 8 pts, nilotinib in 2 pts, dasatinib 1 pt, Hyper CVAD with dasatinib 1 pt, Hyper CVAD with imatinib 1 pt, stem cell transplant 2 pts, bafetinib 1 pt, and unknown 4 pts (lost to follow-up). One pt died shortly after failure without further therapy. Best response to subsequent therapies were 1 pt with CMR (after stem cell transplant), 7 pts with MMR (3 pts after imatinib, 1 pt after dasatinib, 1 pt after nilotinib, 1 pt after Hyper CVAD with imatinib and 1 pt after stem cell transplant), 1 pt CHR, 1 pt minor CyR, 3 pts without response, and 8 pts were not evaluable. Of the 5 pts that achieved MMR with subsequent TKI, all were in CP and had discontinued initial therapy because of toxicity (4 pts) or personal reasons (1pt). Median duration of ongoing subsequent treatment is 8 months (range 1.7–25). The survival rate after a median follow-up of 3.9 months since failure to frontline therapy is 87%.

Failure after frontline therapy with second generation TKI is an uncommon event, most frequently associated with toxicity or patient preference. Most of these patients respond well to alternative TKI. This adequate response should alleviate the fear of not having available effective therapy if patients fail to respond to 2^nd generation TKI when used as frontline therapy.

Kantarjian:BMS: Research Funding; NOVARTIS: Research Funding. Cortes:BMS: Research Funding; NOVARTIS: Research Funding; Pfizer: Consultancy, Research Funding.