Xtandi Does Not Increase Seizure Rates in At-Risk Metastatic Prostate Cancer Patients

by Iqra Mumal

A safety study that looked at the 
treatment of metastatic castration-resistant prostate cancer patients with

Xtandi (enzalutamide) found that the therapy does not increase seizure rates for those who have seizure risk factors.  

The study, “Seizure Rates in Enzalutamide-Treated Men With Metastatic Castration-Resistant Prostate Cancer and Risk of Seizure,” was published in the journal JAMA Oncology.

Xtandi is an androgen receptor inhibitor shown to be effective in treating patients with mCRPC. However, seizures are a known adverse effect of the drug. Various clinical trials have reported patients experiencing seizures while on the treatment.

No previous trials had evaluated Xtandi’s safety for patients with seizure risk factors. Prompted by requests from the 
U.S. Food and Drug Administration and the European Medicines Agency, the UPWARD Phase 4 study (NCT01977651) ex
amined Xtandi’s effect on men with seizure risk factors.

The prospective international safety study took place from September 2013 to February 2016. Participants had at least one risk factor for seizures at baseline, such as medications that lower the seizure threshold, history of stroke, or history of seizures. Patients who had a seizure and required anti-seizure medication within the past 12 months were excluded.

Participants were treated with 160 mg of oral Xtandi per day. The study’s primary objective was to learn the proportion of patients who experienced one or more independently confirmed seizures during the four-month study period.

Among 366 men evaluated, four (1.1%) had one confirmed seizure within four months of starting Xtandi treatment. Three others experienced a seizure within four months after the four-month study period.

The incidence of confirmed seizures was 2.6 per 100 patient-years, or seven seizures. A large retrospective study conducted on patients with mCRPC with similar seizure risk factors but not treated with Xtandi had a similar rate of confirmed seizures (2.8 per 100 patient-years). Researchers determined that the incidence of seizures is similar in mCRPC patients who are at risk of seizures whether or not they were treated with Xtandi.

During the study, 357 patients, or 84.4%, experienced at least one adverse event related to treatment. Additionally, 141 (33.3%) had at least one serious treatment-related event. Thirty-eight deaths (9%) were reported either during treatment or within 30 days of discontinuation. Four of these deaths were possibly related to treatment.

The study suggests that “enzalutamide can benefit patients with a history of seizures or other predisposing factors, but each patient should be closely monitored for the duration of treatment.”

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