Regulators at the Food and Drug Administration have reiterated concerns that Replimune does not have adequate data to support an approval of its investigational skin cancer treatment, as the biotech tries for the third time to seek clearance for its highly controversial drug.

In briefing documents released Tuesday ahead of a meeting of FDA advisers later this week, the agency took issue with the single-arm trial the biotech relies on, in which patients who have already tried a PD1-inhibitor took Replimune’s drug, called RP1, in combination with the PD1-inhibitor Opdivo. The agency argued the study is not enough to properly evaluate the efficacy of the drug itself and whether the treatment, which is injected locally, has systemic benefits.

Replimune counters in its own briefing document that “it is not feasible or ethical” to conduct a study that randomly assigns its drug or placebo on top of PD-1 inhibitors in patients whose cancer has stopped responding to PD-1s, since “there is no evidence that continued anti-PD-1 monotherapy provides any level of clinical benefit” to those patients.