Approach can reduce drug-induced TLS
Photo courtesy of EHA
MILAN—The BCL-2 inhibitor ABT-199 may be a feasible treatment option for patients with chronic lymphocyctic leukemia/small lymphocytic lymphoma (CLL/SLL), according to research presented at the 19th Congress of the European Hematology Association (EHA).
Previous results showed that ABT-199 can elicit responses in patients with CLL/SLL, but it can also induce tumor lysis syndrome (TLS).
In fact, 2 TLS-related deaths prompted the temporary suspension of enrollment in trials of ABT-199.
But now, researchers have reported that a modified dosing schedule, prophylaxis, and patient monitoring can reduce, and perhaps even eliminate, the risk of TLS.
And ABT-199 can produce solid responses, even in high-risk CLL/SLL patients.
John Seymour, MBBS, PhD, of the Peter MacCallum Cancer Center in Victoria, Australia, and his colleagues presented results observed with a TLS prophylactic regimen at the EHA Congress as abstract P868.
Dr Seymour also presented data from a phase 1 study of ABT-199 monotherapy as abstract S702. Both studies were supported by AbbVie and Genentech, the companies developing ABT-199.
Assessing the risk of TLS
To identify pre-treatment risk factors for TLS and appropriate prophylactic measures, Dr Seymour and his colleagues analyzed 77 CLL/SLL patients who were treated with ABT-199 prior to the identification of TLS (from June 2011 to March 2013).
Twenty-four of these patients had values meeting Cairo-Bishop criteria for TLS, and medical adjudication suggested 19 (25%) of them had TLS.
Comparing these patients to those who did not develop TLS, the researchers found that patients were at low risk of developing TLS if they had a nodal mass measuring less than 5 cm and an absolute lymphocyte count (ALC) less than 25,000.
Patients were at medium risk of TLS if they had a nodal mass of 5 cm to 9 cm or an ALC of at least 25,000. And patients were at high risk of TLS if they had a nodal mass of 10 cm or greater or a nodal mass of 5 cm to 9 cm and an ALC of 25,000 or greater.
Dose modification
The researchers also found that TLS events tended to occur within 24 hours of the first dose of ABT-199. And the initial exposure (median Cmax value) for patients who had a TLS incident was higher than patients without TLS (0.49 μg/mL vs 0.23 μg/mL).
However, simulations suggested that, at a 20 mg starting dose, 98% of patients will achieve initial peak exposures similar to patients without TLS (Cmax below 0.23 ug/mL).
So the researchers modified the dosing schedule of ABT-199 in subsequently treated patients. The patients received a 20 mg starting dose, then 50 mg for the rest of week 1, 100 mg in week 2, 200 mg in week 3, and 400 mg in week 4.
However, if 1 or more electrolytes met Cairo-Bishop criteria and/or there was a 30% or greater decrease in ALC with the first dose, patients received the drug at 20 mg in week 1, 50 mg in week 2, 100 mg in week 3, 200 mg in week 4, and 400 mg in week 5.
Prophylactic measures
Dr Seymour and his colleagues also recommended several other steps to minimize the risk of TLS. They said their findings support hospitalizing and monitoring patients for the first dose of 20 mg and 50 mg, regardless of their risk of TLS.
High-risk patients should be hospitalized for all subsequent dose escalations until they are re-categorized to medium- or low-risk groups. The researchers also said hospitalization should be considered at subsequent dose escalation for medium-risk patients with creatinine clearance of 80 mL/min or less.
