No longer a hand-me-down approach to WM
Photo courtesy of DFCI
NEW YORK—Whole-genome sequencing has changed the entire approach to drug development for Waldenström’s macroglobulinemia (WM), according to a speaker at Lymphoma & Myeloma 2016.
The strategy has changed from a hand-me-down one, relying on drugs developed first for other diseases, to a rational plan designed specifically to treat WM patients.
“We would wait for our colleagues in the myeloma world or lymphoma world, CLL world, anywhere we could find them, to help us with the development of drugs,” said Steven Treon, MD, PhD, of the Dana-Farber Cancer Institute in Boston, Massachusetts.
“And, sometimes, this resulted in delays of many, many years before those therapeutics could be vetted out and eventually be handed down to the Waldenström investigators.”
At Lymphoma & Myeloma 2016, Dr Treon described the current therapy of WM and the impact of the discovery of MYD88 and CXCR4 on drug development and treatment choices in WM.
Rituximab-based therapy
WM is a disease that strongly expresses CD20, even though it’s a lymphoplasmacytic disease. So rituximab, given alone and in combination, has been, to date, the most common approach to treating WM.
As a single agent, rituximab produces a response in 25% to 40% of WM patients, but these are very seldom deep responses, Dr Treon noted.
So investigators combined rituximab with cyclophosphamide, nucleoside analogues, proteasome inhibitors, and bendamustine, which increased the overall response rate and depth of response.
This translated into improvement in time to progression, which is now 4 to 5 years with these combination therapies.
“Now, the problem is, when you borrow things from other people, you sometimes end up with problems you didn’t anticipate,” Dr Treon said.
One of the unanticipated side effects with rituximab in WM patients is the IgM flare, which occurs in 40% to 60% of WM patients.
Rituximab can also cause hypogammaglobulinema, leading to infections, and results in a high intolerance rate, which tends to occur a few cycles into induction or maintenance therapy.
“In some cases,” Dr Treon advised, “a switch to ofatumumab, a fully human CD20 molecule, overcomes this intolerance.”
Nucleoside analogues, which used to be the mainstay of WM, have a high rate of transformation into a more aggressive lymphoma or acute myeloid leukemia.
Immunomodulatory drugs, particularly thalidomide, cause peripheral neuropathy greater than grade 2 in 60% of patients.
And a greater incidence of peripheral neuropathy is also observed with proteasome inhibitors, particularly bortezomib, in WM patients than in myeloma or mantle cell lymphoma patients.
“So this was at least the impetus for why we needed to develop novel approaches to treating this disease,” Dr Treon said.
MYD88 mutations
With whole-genome sequencing, investigators discovered that mutations in the MYD88 gene were highly prevalent in WM patients.
About 93% to 95% of WM patients have the L265P MYD88 mutation, and about 2% have the non-L265P MYD88 mutation.
MYD88 has prognostic significance in WM. Mutated MYD88 confers a better prognosis than unmutated MYD88.
MYD88 may also be important in predicting who will respond to drugs like ibrutinib.
CXCR4 mutations
Mutations in CXCR4 are the second most common mutation in WM.
Between 30% and 40% of WM patients have the WHIM-like CXCR4 C-tail mutations, which traffic the Waldenström’s cells to the bone marrow.
This mutation promotes drug resistance, including resistance to ibrutinib because of the enhanced AKT/ERK signaling.
Ibrutinib therapy
With this in mind, investigators set out to evaluate the potential of using a BTK inhibitor in relapsed/refractory WM patients and at the same time observe the genomics that might predict for response and resistance.
