Less than half of the clinical trial data underpinning the approval of anticancer drugs are available for independent scrutiny despite an industry pledge for greater transparency, Australian and US researchers say.

Their audit of US regulatory approvals since 2011 shows that for three of the globally top-selling cancer drugs — nivolumab, pembrolizumab and pomalidomide — less than 10% of trial data were publicly available.

Nivolumab and pembrolizumab are the most expensive chemotherapy drugs for Australian taxpayers, with a cost to the PBS of more than $800 million in 2020-21 alone, the researchers say.

“Because these trials form the basis of safety and efficacy claims for new medicines, we question whether it is justified that the data are unavailable to independent scrutiny,” the authors write.