NEW YORK — In the wake of details about the molecular pathophysiology of Waldenström macroglobulinemia (WM), an expert gave an update on current and expanding options for treatment.
Most importantly, determining the mutational status of patients with WM has become a first or early step in guiding first- and second-line therapies, according to Edward Stadtmauer, MD, professor of medicine, University of Pennsylvania, Philadelphia.
Presenting at the 2024 Lymphoma, Leukemia & Myeloma Congress in New York City, Stadtmauer discussed how MYD88 and CXCR4 gene mutations influence his therapeutic choices.
While delivering the Bruce Waterfall Memorial Lecture, funded by the International WM Foundation, he explained that the vast majority of patients with WM have a MYD88 mutation that is highly sensitive to Bruton tyrosine kinase (BTK) inhibitors.
Due to greater specificity on the BTK target, which has implications for safety and efficacy, the first-generation BTK inhibitor ibrutinib has been largely supplanted by next generation drugs such as zanubrutinib.
Deep Responses in WM Remain Elusive
The support for next-generation BTK inhibitors over ibrutinib; bendamustine plus rituximab (BR); or cyclophosphamide, bortezomib, and dexamethasone (CyBorD) is, in his opinion, “a superior toxicity profile, high response rates, and prolonged response.” However, he conceded that the weaknesses of this approach include a low chance of a deep remission and the need for continuous therapy.
On account of these limitations, he typically favors the alkylating agent bendamustine plus the anti-CD20 rituximab over BTK inhibitors in the absence of MYD88 mutations. This once standard approach has become less commonly used in the era of BTK inhibitors, but it is also highly effective, is generally administered in a time-limited regimen, and may be more likely to push patients into a deep remission.
A similar rationale might be considered for CyBorD, but Stadtmauer believes that BR provides a higher rate of PFS with a lower risk for neuropathy, although he admitted this opinion is based on cross-study comparisons, not comparative trials.
While efforts to develop therapies capable of producing a deep response “should not be abandoned,” particularly with the T-cell engager therapies on the horizon, he is not convinced that the benefit-to-risk ratio of aggressive therapies is yet warranted in a disease the often progresses slowly.
“I must admit I am still under the philosophy that Waldenström’s is a chronic disease even if we are seeing a growing list of options for relapsed or poorly responding disease, so I am still not pushing patients too aggressively to knock them into a complete remission,” he said.
MYD88 mutations are not unique to WM, an uncommon, slow-growing form of non-Hodgkin lymphoma. They are found in a small proportion of patients with other hematologic disorders, such as marginal zone lymphomas, but Stadtmauer estimated they occur in 90% of patients with WM. They are common enough that they can help with diagnosis.
CXCR4 Mutations Predict Worse Outcomes
The CXCR4 mutation occurs in an estimated 40% of patients with WM. When present, they are associated with worse outcomes, including a faster time to progression and a reduced overall survival, according to Stadtmauer.
The prognostic impact of less common mutations, such as TP53 and TERT or deletions in LYN, are less well characterized, but Stadtmauer said that most mutations associated with WM result in constitutive or continuous activation in BTK, which, in turn drives WM cell proliferation and survival.
The importance of BTK in WM progression is the reason targeted inhibitors have assumed such a key role in first-line treatment, but Stadtmauer cautioned that these drugs, like other therapies, should not be initiated in asymptomatic patients. This has been stated in past and current guidelines.
More accurately, therapy should be held until just prior to symptomatic manifestations of disease, Stadtmauer specified.
For an optimal response, “you want to start therapy about 3 or 4 months before the symptoms begin,” said Stadtmauer characterizing efforts to do so as “the art of medicine.” Starting therapy just prior to symptoms is advantageous, but it involves following patients closely. Any single biomarker might not be enough.
“In an asymptomatic patient, the level of monoclonal IgM is not an indication to start therapy,” he said, citing studies showing no effect on subsequent disease control from treating this biomarker alone.
However, he listed the development of moderate peripheral neuropathy (PN) as an exception. Essentially, anything greater than mild PN is “still bad” in Stadtmauer’s opinion, so treatment is warranted.
The growing number of second-line options relieves some of the concern when patients progress. Stadtmauer said he is now using BR more often in the second-line drug now that he is using BTK inhibitor more in the first line.
The Bcl-2 inhibitor venetoclax is highly effective and is another first- or second-line option even if this agent, like BTK inhibitors, also appears to require continuous dosing, said Stadtmauer, citing a study that showed patients relapsed relatively rapidly when the drug was stopped.
He now thinks of regimens with proteasome inhibitors as third line.
In selected patients who do not tolerate the non-covalent second-generation BTK inhibitors in the first or second line, he said, “I move quickly to the covalent BTKi pirtobrutinib,” based on data suggesting responses that are at least as good but with a better tolerability profile.
T-Cell Engager Data Are Limited
Without spending much time on the T-cell engagers, such as CAR T-cells or bispecific antibodies, Stadtmauer said that the advances he sees on the horizon “are tremendous,” and the “future is bright.” Such approaches could yield deep responses that could extend control or even provide cure, but these are speculations until more patients have been treated and followed long term.
Morton Coleman, MD, director of the Center for Lymphoma and Myeloma at Weill Cornell Medicine and the chairperson of the LLM Congress, called the talk a valuable and practical summary from a knowledgeable source. BTK inhibitors have represented a major evolution in WM management, but Coleman appreciated the underlying concept that treatment still has to be individualized.
“I think one of the most important take home messages is that the characterization of the mutational profile in patients with Waldenström should be considered a standard of care,” Coleman said. Helpful now, the mutational profile is likely to have a more valuable role as treatment is increasingly individualized.
Stadtmauer reported financial relationships with AbbVie, Bristol Myers Squibb, Celgene, Janssen, and Sorrento. Coleman disclosed ties with AbbVie, AstraZeneca, BeiGene, Bristol Myers Squibb, Gilead, Loxo Oncology, Janssen, and Pharmacyclics.
Ted Bosworth is a medical journalist based in New York City.
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