Antipsychotic clozapine raises blood cancer rates; overall risk is small
Researchers reviewed outcomes for about 10,000 people with schizophrenia
Treatment with the antipsychotic medication clozapine may increase the risk of blood cancers, but their overall likelihood is still low in people taking the drug, a study reports.
The results suggest “patients do not need to be overly concerned about the risk of blood cancer caused by clozapine given the rarity of its occurrence demonstrated in this study,” Francisco Lai Tsz-tsun, PhD, co-author of the study at the University of Hong Kong, said in a press release.
The study, “Rare but elevated incidence of hematological malignancy after clozapine use in schizophrenia: A population cohort study,” was published in PLOS Medicine.
Psychosis is a mental health condition characterized by hallucinations, that is, seeing or hearing things that aren’t real, and/or delusions, which are fixed beliefs with no basis in observable reality. Clozapine, sold as Versacloz and Clozaril, is an antipsychotic medication that may be used to manage psychosis in people with schizophrenia.
Emerging data suggests clozapine may statistically increase the risk of blood cancers, but getting a solid estimate on exactly how much of a risk is associated with the medicine has been difficult.
Comparing blood cancer risk
Here, scientists combed through a healthcare database in Hong Kong and looked at outcomes for nearly 10,000 people with schizophrenia who were followed for a median of about seven years to get a more exact estimate.
“Because of the readily linked and longitudinally available data across all public healthcare facilities in Hong Kong, we were able to come up with a better study design than those in other countries,” Lai said. “This enabled us to make immediate use of big data to better address clinically meaningful healthcare issues than researchers in many other countries, highlighting the key strengths of Hong Kong’s healthcare big data and its potential application in drug safety monitoring.”
The researchers compared the risk of blood cancer in patients given clozapine to the risk in patients on olanzapine, another antipsychotic that’s sold as Zyprexa, among others.
“Olanzapine was chosen as a comparator due to its similar chemical structure and increasing advocacy in recent years for it to serve as an alternative to clozapine for treatment-resistant schizophrenia,” the researchers wrote.
The risk of blood cancer was about twice as high with clozapine, the results showed, lending credence to the idea that it does indeed increase the risk of blood cancers. Still, blood cancers were extremely rare; of more than 830 patients given clozapine, only nine developed blood cancer. Put another way, if there were 100,000 patients given either clozapine or olanzapine for a year, the data suggest about 57 more patients given clozapine would develop blood cancer.
“Findings from this territory-wide cohort study involving approximately 10,000 individuals with schizophrenia in Hong Kong suggested a rare, but [twofold] increased rate of [blood cancer] associated with clozapine compared to olanzapine. Nevertheless, the absolute rate difference is small, with less than 60 additional cases of [blood cancer] per 100,000 person-years of clozapine use compared with olanzapine use,” wrote the researchers, who said the data may help people with schizophrenia and their clinicians when considering the risks and benefits of treating with clozapine.
“Clinicians should weigh the risks and benefits of the drug, taking into account the rarity of the association between clozapine and blood cancer, and make appropriate arrangements according to patients’ needs,” Lai said.
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