Conference Coverage

ITP: Biologic beat placebo, but few patients improved


 

AT ASH 2022

Patients with chronic immune thrombocytopenia (ITP) fared better on intravenous efgartigimod (Vyvgart) than a placebo, a new study found. Still, only 21.8% of subjects who received the biologic reached the primary endpoint of sustained platelet count response, an indication that most patients won’t benefit.

Nevertheless, “efgartigimod demonstrated a strong clinical benefit,” said hematologist/oncologist and study lead author Catherine M. Broome, MD, of Georgetown University, Washington, in an interview about the findings presented at the annual meeting of the American Society of Hematology.

Dr. Catherine M. Broome, MD, hematologist/oncologist, Georgetown University, Washington, D.C.

Dr. Catherine M. Broome

“The data showed statistically significant and clinically meaningful improvement in platelet counts over placebo, a fast and robust platelet count improvement over placebo, and the confirmed ability for every-other-week dosing, as well as a favorable safety and tolerability profile, consistent with previous clinical trials,” she said.

In ITP, according to the National Organization for Rare Disorders, “the patient’s immune system tags their own platelets as ‘foreign,’ leading their B lymphocytes and plasma cells to produce self-reactive antiplatelet antibodies that attach to platelet surface.”

The prevalence of ITP among adults in the United States is 9.5 per 100,000, NORD says. Children are also affected, but they usually recover. An estimated 60% of adults recover within 3 years.

Treatment options include corticosteroids and intravenous immunoglobulin.

“There are a relatively large number of current treatments, and they tend to work well for most patients. However, there are a minority of patients who do not respond to or tolerate current therapies and would benefit from new treatment options,” said hematologist Adam C. Cuker, MD, MS, of Penn Medicine, Philadelphia, in an interview. He is chair of ASH’s Committee on Quality.

For the new industry-funded ADVANCE study, researchers recruited patients with long-standing, persistent/chronic ITP (an average of two platelet counts of < 30×109/L).

Subjects were randomized 2:1 to receive 10 mg/kg of efgartigimod weekly – or response-dependent doses after the first 4 weeks – or placebo for 24 weeks. There were 86 patients in the intervention group and 45 in the placebo group. Overall, 60 were male and 71 were female; 107 were under 65; 121 were White and 8 were Asian. Details about the others were not provided.

Subjects were allowed to take several other drugs such as oral corticosteroids, and oral thrombopoietin receptor agonists other than romiplostim.

Per the primary endpoint, 17/78 (21.8%) reached a sustained response, defined as platelet counts ≥ 50×109/L in ≥ four of six visits between weeks 19 and 24 without intercurrent events, such as rescue therapy at week 12 or later. In the placebo group, 2/40 reached this response (5.0%; P = .0316).

“The primary endpoint was a high bar to achieve,” Dr. Broome said. “This was a difficult-to-treat patient population heavily pretreated and refractory to other treatments: 68.6% of patients in the efgartigimod arm had received three or more prior ITP treatments.”

She added that “subgroup analyses – including prior ITP therapy, time since diagnosis, baseline platelet count and age/region demographics – of patients who achieved the primary endpoint all favored efgartigimod over placebo.”

Side effects were extremely common among both the drug and placebo groups, and serious adverse events were common in the placebo group. No deaths were reported.

Efgartigimod, a neonatal Fc receptor blocker, is an extremely expensive drug that is Food and Drug Administration approved for some cases of generalized myasthenia gravis. According to a report in Neurology earlier this year, company statements listed its price as $855,400 a year; the report questioned its cost-effectiveness.

In response to a query about price, Luc Truyen, MD, PhD, chief medical officer of drug manufacturer Argenx, declined to talk about cost – a sensitive topic for pharmaceutical companies. “It is too early to discuss pricing and access as no regulatory submission or discussion has occurred,” Dr. Truyen said.

Penn Medicine’s Dr. Cuker, who is familiar with the study findings, said the primary endpoint results are not very impressive. “That said, it should be borne in mind that the patients enrolled in the trial tended to be heavily pretreated and refractory patients,” he said.

As for adverse effects, he said the drug “appears to be safe and well tolerated. The biggest theoretical concern with this class of drugs is an increased risk of infection due to lowering of IgG levels.”

It would be helpful to have trials that directly compare second-line therapies in ITP, he added. “Unfortunately, no such trials exist, and pharmaceutical companies would not be motivated to conduct them.”

For now, he said, off-label use of efgartigimod “may be reasonable, but only in rare situations where other approved and better established ITP treatments have been exhausted.”

What’s next? According to Dr. Broome, another trial is currently evaluating efgartigimod for the treatment of primary ITP, with top-line data expected in the second half of 2023.

The study was funded by Argenx. Dr. Broome discloses honoraria from Alexion, Argenx, Apellis, and Sano. Dr. Truyen’s disclosures weren’t available. Dr. Cuker has no disclosures.

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