An expert panel has advised the FDA to approve a new kind of device
to treat recurrent glioblastoma, an aggressive and highly fatal kind of brain tumor.
The FDA is not required to follow the recommendations of its advisory panels, though it commonly does.
The NovoTTF-100A System (NovoTTF) is designed to treat tumors by
zapping them with an intermediate-frequency electrical field that’s
generated by a 6-pound battery pack that a patient carries in a satchel
or backpack.
It has been studied for use in patients whose cancer has returned after treatment with standard treatments such as surgery, radiation, and chemotherapy.
The device has two parts: the battery pack and wires that attach
to a sheath of electrodes that are attached to the scalp. The
rechargeable batteries must be replaced every three hours. And patients
are advised to wear the electrodes for at least 18 hours.
The twelve voting members of the Neurological Devices Advisory
Panel were asked to vote on three questions: whether or not they
considered the device to be safe; whether they considered it to be
effective; and whether or not the benefits of using the device
outweighed the risks.
Split Vote on Effectiveness
The panel voted 12-0 that the device was safe enough for use in a terminally ill population.
On the question of effectiveness, however, the panel was deeply
divided, and the vote split with six members voting yes and six voting
no.
The chairman of the panel, Robert Hurst, MD, a professor of
radiology at the Hospital of the University of Pennsylvania, was called
on to break the tie. He voted yes.
In the final vote, on whether the benefits outweighed the risks, the vote was 7 yes, 3 no, with 2 members abstaining.
In explaining her votes, Sarah H. Lisanby, MD, chair of the department of psychiatry and behavioral sciences at Duke University School of Medicine, voiced the concerns of many on the panel.
“I think that the technology this is based on could be a real breakthrough,” she says.
Lisanby, like many on the panel, was concerned by the small size
and design flaws that likely biased the results of the clinical trial
that was presented to determine approval.
The trial included 237 patients who were randomly assigned to receive either the NovoTTF or chemotherapy.
But in analyzing their data, the researchers did not consider
patients who could not complete at least four weeks of therapy with the
NovoTTF. Some of those were among the sickest patients in the trial, and
panel members felt that their exclusion, along with design problems,
likely biased the results in favor of the new device.
Overall, the study found that patients survived about as long
using the NovoTTF as they did with chemotherapy, with significantly
fewer side effects. But many felt that result wasn’t definitive.
“There’s still a need for more systematic assessment,” Lisanby says.
She voted that the device was not proven to be effective and was
one of two voters who abstained on the question of whether the benefits
outweighed the risks.
“I didn’t know how to make a ratio between safety and efficacy when neither was well measured,” she says.
Study researchers reported very few side effects while using the NovoTTF. A skin rash, which developed beneath electrodes, was the most common problem and it could be treated with topical steroids.
