Ongoing Trial Demonstrates Promising PFS With Ibrutinib in Hairy Cell Leukemia

Danielle Ternyila
Published: Friday, Oct 25, 2019

Kerry Rogers, MD, assistant professor at The Ohio State University Comprehensive Cancer Center

Kerry Rogers, MD

Patients with hairy cell leukemia have limited options. Purine nucleoside analogues (PNA) have provided benefit and promising responses to many patients with hairy cell leukemia, but more options are required for those patients who relapse. Data from an ongoing trial demonstrating promising results with ibrutinib (Imbruvica) were presented at the 2019 Hairy Cell Leukemia Foundation Annual Conference.

The phase II trial of ibrutinib (NCT01841723) began enrolling patients with hairy cell leukemia of both the classic and variant subtype in 2013, and 39 patients have been enrolled to date, with 38 having started treatment with ibrutinib. However, the data presented are from a smaller group of these patients as it has taken 6 years to fully accrue the trial due to the rarity of this disease.

The overall response rate (ORR) in this patient population is 50%, and while the principal investigator on the study, Kerry Rogers, MD, notes that this may not be an outstanding response, she says it is promising for such a rare type of leukemia. Additionally, the progression-free survival (PFS) rate at 3 years was nearly 75%, which Rogers says is impressive, given that these patients were, for the most part, not responding to standard treatments.

In an interview with OncLive, Rogers, assistant professor at The Ohio State University Comprehensive Cancer Center, discussed the potential of ibrutinib in hairy cell leukemia, emerging treatment options such as moxetumomab pasudotox (Lumoxiti), and next steps and challenges in the field.

What was the rationale for evaluating ibrutinib in patients with hairy cell leukemia?

As most people know, ibrutinib is an oral targeted inhibitor of BTK. This has been a really important target, and it has been FDA-approved in 4 different B-cell malignancies. There’s an unmet need for new therapies for the subset of hairy cell leukemia patients who don’t respond to PNA or don’t benefit from them anymore or as much as we want. Therapies that work in chronic lymphocytic leukemia (CLL) and other B-cell cancers frequently do work in hairy cell leukemia; in particular, CLL and hairy cell leukemia have some overlap for therapies that work. Since ibrutinib is available and potentially effective (especially for patients who might not benefit from chemotherapy), we decided to evaluate [the BTK inhibitor] in hairy cell leukemia.

How was this study designed?

It’s a single-agent study, and it is a phase II study. In this study, everyone receives treatment with ibrutinib once daily. The ibrutinib dose is administered continuously until either patients progress, don’t tolerate ibrutinib, or decide to stop therapy. That is the way it is given in other diseases.

The study was opened in 2013 and designed before that. At the time the study was designed, not as much was known about ibrutinib compared to what we know now. There were 2 different dose levels used in the study, 420 mg and 840 mg. Ultimately, the 420-mg dose was the dose we decided to move forward with. There was no difference in response or toxicity that we could discern between the 420 mg and 840 mg doses. However, the sample size was pretty small, so it was hard to tell, but since the 420 mg dose was effective and used in other diseases, such as being the approved dose in CLL, that is what we have been treating people with who are enrolled in the study more recently.

What were the results from this study?

We have enrolled 39 patients now, and 38 have started on treatment. This is substantial for a hairy cell leukemia study, but as the study has accrued over 6 years, due to the rarity of this patient population, the longest follow-up we have is from a smaller group of patients who were enrolled earlier.

We found that the ORR for best response, meaning the best response that patients achieved at any time, is just over 50%. That may not seem like an outstanding response rate, but that’s really because of the rigor of response criteria. A lot of patients who didn’t meet criteria for response did have a very substantial clinical benefit. The estimated 3-year PFS is just under 75%. Even though you only have just half of the patients responding, at 3 years, just under 3-quarters had not had disease progression and are alive. Really, the PFS has been very good with this study, and I think that’s the major benefit of this drug.

What else is significant about the study findings?

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