BioMarin Pharmaceutical will need to run additional preclinical studies to assess the “theoretical” cancer risk of a rare disease gene therapy it’s developing, information the Food and Drug Administration requested to resolve a clinical hold the agency placed on human tests of the treatment last fall.

Running those studies and collecting the asked-for data will take “several quarters,” BioMarin said in a statement Thursday. The company will disclose next steps “when available.”

The FDA’s hold came after a study in mice run by BioMarin found the virus used to shuttle functional copies of the target gene into cells fused into the genomes of six mice which had developed liver cancer. The mice were given a much higher dose by weight of the gene therapy than used in initial human testing, however.

While other studies have shown similar risks in mice, they haven’t been observed in larger animals or in people.