Vascular events in CML may not be linked to TKI therapy

By Laura Cowen

The increased risk of vascular events observed among elderly patients with chronic myeloid leukaemia (CML), compared with patients without cancer, may not be driven by tyrosine kinase inhibitor (TKI) therapy, US researchers suggest.

Kathy Lang, from Quintiles in Cambridge, Massachusetts, and her study co-authors believe that "underlying risk factors associated with CML" could be the reason for the excess risk of vascular events reported in these patients .

"These findings are likely to be of interest to clinicians considering TKI treatment for patients with CML", they write in Clinical Lymphoma, Myeloma and Leukemia.

Using linked Surveillance, Epidemiology, and End Results cancer registry and Medicare claims data, the researchers identified 1466 patients (56% men) diagnosed with CML between 2004 and 2009 and matched them to a noncancer control.

Both groups had a mean age of 78 years, but the mean follow-up period was significantly shorter among the CML patients than the control group (25 vs 42 months) because the CML patients had significantly higher mortality (62.7 vs 23.1%) during follow-up.

Patients with CML, compared with noncancer patients, also had significantly higher rates of myocardial infarction (MI, 33.0 vs 11.9 per 1000 person-years), stroke (83.2 vs 43.0 per 1000 person-years), pulmonary embolism (PE, 6.6 vs 2.6 per 1000 person-years) and peripheral arterial disease (PAD, 92.1 vs 59.3 per 1000 person-years).

Only 15% of patients with CML received TKI therapy, most commonly imatinib, which was given in 97% of cases. The researchers found that these patients had similar survival rates to those in the noncancer cohort, with 18.3% dying during a mean follow-up period of 42 months.

Furthermore, TKI-treated CML patients had similar or lower rates of MI (30.5 vs 33.9 per 1000 person-years), stroke (58.9 vs 91.0 per 1000 person-years), PE (3.9 vs 7.5 per 1000 person-years), and PAD (89.6 vs 92.9 per 1000 person-years) compared with CML patients without evidence of TKI therapy.

And although multivariate analysis showed that CML patients had a significantly increased risk of death (hazard ratio [HR]=4.2), MI (HR=2.5) and stroke (HR=1.5) during follow-up compared with controls, receipt of TKI was not significantly associated with either MI or stroke among the CML cohort.

Discussing the limitations of their study, Lang et al note that the low number of patients receiving TKI treatment prevents them from drawing any firm conclusions.

They add that they could not analyse data for patients receiving dasatinib or nilotinib owing to the small number of patients who received these drugs.

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