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Rituximab maintained 5-year response in a quarter of ITP patients
About 25% of adults and children who responded to rituximab for the treatment of immune thrombocytopenia were able to maintain a treatment-free response for at least 5 years, according to the results of a large cohort study.
Current treatments available for immune thrombocytopenia (ITP) that provide a durable treatment-free response are limited.
“Treatments of patients with chronic ITP which provide a curative effect without untoward toxicity or poor tolerability are highly desirable,” the researchers wrote. “They allow a patient to avoid the disadvantages of low platelet counts, including continued platelet count monitoring, continued treatment and possibly bleeding and/or fatigue.”
In this study, the researchers projected relapse-free 5-year sustained response in a group of 138 patients who had been treated with rituximab (Rituxan, Genentech) and shown either complete response or partial response. The cohort included 72 adults who had treatment response of at least 1 year and 66 children with any response.
Patients received the standard dose of rituximab — four weekly infusions of 375 mg/m2 per infusion. For this study, complete response was defined as a platelet count of >150 X 109/L, and partial response was defined as platelet count between 50 and 150 X 109/L.
The initial overall response rate among children was 57%, and the 1-year response rate was 33%, the researchers said. Based on the data, the researchers estimated the 5-year response rate for children with ITP was 26%.
The initial overall response rate among adults also was 57%, and more than half of adults had a response that lasted more than 1 year. Based on the data, the researchers estimated the 5-year response rate was 21%.
No novel or long-term treatment-related toxicities occurred.
“Ultimately, further understanding of the mechanism of action of rituximab and its potential interactions with the immune system, and other treatments, is needed to safely maximize the number and duration of long-term responses,” the researchers wrote.
Perspective
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Rituximab has become a standard second-line treatment for patients with primary immune thrombocytopenia (ITP). The frequency of its use is about the same as splenectomy. More than 50 years of observational data on splenectomy have documented consistent long-term response rates of 60% to 65%. There were no comparable data for long-term response rates with rituximab treatment until this landmark publication by Patel and colleagues. With an effective collaboration of nine centers in five countries, estimated 5-year response rates of 21% for adults and 26% for children are reported. These will become the data that we will now use for our discussions and decisions with our patients. In addition, this is a perfect example of the importance of collaborative observation studies to define long-term outcomes for uncommon disorders.
Perspective
Back to TopDespite a lack of clinical trials data and regulatory approval for its use, rituximab has been widely used to treat ITP. Platelet count increases in the first 1 to 2 weeks may reflect an IVIG-like effect, and later platelet responses may truly be due to immune modulation. The study by Patel and colleagues provides a very helpful assessment of the role Rituximab may play in the treatment of ITP — initial response rates in a little over half of patients, lasting for 1 year in about 37%, with long-term responses at 5 years around 20% to 25%. Whether these long-term responses are due to Rituximab or simply reflect the natural history of ITP will remain unclear. These data support the low rating given for Rituximab treatment in the recent ASH ITP guidelines.
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