Patients with chronic myeloid leukemia (CML) treated with imatinib are much more likely to die from their comorbid conditions than from the leukemia, according to a report published in Blood.

During the past decade, CML has been transformed from a routinely fatal disease to a chronic condition controlled by regular drug therapy using imatinib and newer tyrosine kinase inhibitors. The influence of comorbidities on survival outcomes has not been studied until now, said Dr. Susanne Saussele of Heidelberg University, Mannheim (Germany), and her associates.

They used data from a large German study of first-line imatinib therapy, focusing on 1,519 CML patients who were evaluable after a median follow-up of 68 months. Approximately 40% of these study participants had one or more of 511 evaluable comorbidities. The most common conditions relevant to CML and its treatment were diabetes, nonactive cancer other than CML, chronic pulmonary disease, renal insufficiency, MI, cerebrovascular disease, heart failure, and peripheral vascular disease.

Study participants were categorized by the number and severity of their comorbidities using the Charlson Comorbidity Index as CCI 2 (589 patients), CCI 3 or 4 (599 patients), CCI 5 or 6 (229 patients), or CCI 7 and above (102 patients), with higher levels indicating a greater burden of comorbidity. Overall 8-year survival probabilities directly correlated with CCI category, at 94% for CCI 2, 89% for CCI 3 or 4, 78% for CCI 5 or 6, and 46% for CCI 7 or above. In addition, CCI score was the most powerful predictor of overall survival, the researchers said ( Blood 2015;126:42-9 ).

Comorbidities had no impact on the success of imatinib therapy. Even patients with multiple or severe comorbidities derived significant benefit from imatinib, and comorbidities had no negative effect on remission rates or disease progression. Taken together with comorbidities’ strong influence on mortality, this indicates that patients’ survival is determined more by their comorbidities than by CML itself, Dr. Saussele and her associates said.

Their findings also showed that overall survival alone is no longer an appropriate endpoint for assessing treatment efficacy in CML. Progression-free survival seems to be a more accurate measure of treatment effect, since it was not influenced by comorbidities in this study, they added.