A Retrospective Real-Life Analysis of Chronic Myeloid Leukemia Patients in Suboptimal Response to Imatinib

Abstract 4446

Life expectancy of CML patients has greatly improved in tyrosine-kynase inhibitor (TKI) era, but still some questions remain about the management of suboptimal responders (SR) to imatinib standard dose. This group of patients appears to be heterogeneous, with significant differences in terms of event-free survival between cytogenetic SR and molecular SR (Alvarado et al, Cancer 2009)

European Leukemia Net (ELN) recommendations did not clarify those differences and there isn't a clear agreement on SR: maintaining imatinib at standard or higher dose or switching to another TKI are all considered acceptable options (Baccarani et al, JCO 2009).

We retrospectively analyzed 63 CML patients, diagnosed in chronic phase between 1988 and 2011, SR to imatinib 400 mg/d, treated according to the 3 different ELN options. Fifty-two patients received imatinib front line and 11 had been previously treated with an interferon based therapy. Sokal score, evaluable in 44 patients, was high in 7, intermediate in 24 and low in 12, respectively. Twenty-five patients were cytogenetic SR and 38 molecular SR. The median follow-up from diagnosis was 76 months (range 10–292).

At suboptimal response detection 47 patients (74%) continued imatinib 400 mg/d (30 of them afterword switched to high dose imatinib or new TKI), 12 patients (19%) increased imatinib dose to 600 mg/d (7) or 800 mg/d (5) (8 of them later changed TKI) and only 4 patients switched immediately to new TKI.

Twenty-three percent of the 47 patients who continued imatinib 400 mg/d obtained a stable complete cytogenetic response (CCyR) and major molecolar response (MMR) while 27% underwent to a failure. Globally thirty-tree SR patients increased imatinib dose, 36% at suboptimal response detection and 64% after a median of further 12 months of standard dose treatment (range 3–50): 48% of them obtained a durable CCyR and MMR. Twenty-six evaluable patients switched to new TKI (9 to nilotinib and 17 to dasatinib), 13 after high dose imatinib: 62% of the patients achieved a stable CCgR and MMR. Both high dose imatinib and new TKI were significantly more effective in achieving CCyR and MMR than maintaining imatinib 400 mg/d (p<0,05).

Considering separately the subgroup of cytogenetic SR patients, a stable CcyR has been reached by 35% of patients continuing imatinib standard dose, by 50% of the patients who increased imatinib dose and by the totality of the patients treated with new TKI (option significantly superior to the other two, p<0,05).

Among molecular SR, 26% of the patients obtained a stable MMR with imatinib 400 mg/d, 52% with imatinib 600 or 800 mg/d and 63% switching to new TKI. The difference was statistically significant between new TKI and imatinib 400 standard dose only (p<0,05).

Cytogenetic SR maintained at imatinib 400 mg/d had a higher risk of event (defined as loss of hematologic or cytogenetic response or death) compared to molecular SR (40% vs 5%, p<0,01), although at the last follow-up, after a change in therapeutical strategy, no difference in response rate was detected between cytogenetic and molecular SR (68% vs 71%) in stable CCyR and MMR.

Two patients progressed to accelerated phase (clonal evolution) but then obtained an optimal response after switching to new TKI; 2 patients died of unrelated disease. Among the 61 living patients, 71% was in MMR, 26% in CCyR only and 3% didn't reach CCyR (for these patients the efficacy of the therapeutic change is not evaluable yet).

In our casistics cytogenetic SR had a higher risk of negative events than molecular SR, as reported in literature, although they obtained similar responses after changing therapeutic strategy. No clear advantage in maintaining imatinib 400 mg/d after suboptimal response was observed, since it led to a few optimal responses and was associated with a significant risk of treatment failure. Imatinib dose increment might represent a more reasonable option, at least for molecular SR.

Considering the global casistic no significant difference in response rates were found between new TKI and high dose imatinib even if dasatinib and nilotinib showed a trend towards a superior efficacy in patients mostly unresponsive to the last option, suggesting that an earlier switch to new TKI might further increase the proportion of optimal responders. For cytogenetic SR the switch to new TKI brought better results than those obtained with high dose imatinib: therefore it seems to be the best choice in this subgroup of patients.