Nonadherence to Imatinib adversely affects event free survival in chronic phase chronic myeloid leukemia

There is limited data on the impact of treatment interruptions due to nonadherence in patients with chronic phase chronic myeloid leukemia (CP-CML) treated with Imatinib. We looked at factors (including adherence to therapy) affecting the outcome in a large cohort of patients with CP-CML. All the 516 patients received Imatinib free-of-cost through a company sponsored scheme, which mandated regular three monthly visits for drug procurement. Data regarding the disease characteristics, adherence to treatment and outcomes, were obtained from patients records. Unwarranted interruption of treatment for more than 1 week was defined as nonadherence. With a median follow-up of 39 months, the estimated 5-year event free survival (EFS) was 70.8% (95%, CI = 63.3-78.3). Nearly one-third of the patients (29.6%) were found to be nonadherent at some point during their treatment. On univariate analysis, the factors adversely affecting the EFS were prolonged symptom duration before diagnosis, treatment with hydroxyurea for more than 1 month before start of Imatinib, and nonadherence to therapy. Only nonadherence was significant in multivariate analysis (HR1.6; P = 0.048). The 5-year EFS in adherent and nonadherent patients was 76.7% and 59.8% respectively (P = 0.011, log rank test). Nonadherent patients were less likely to achieve complete cytogenetic responses (26% versus 44%; P = 0.004; χ(2) test) at any point. A significant proportion of patients with CP-CML have drug interruptions due to nonadherence during therapy and this compromises the EFS. Adherence to therapy must be included as an important evaluation parameter in all future studies of CML.