Cass Report has ‘high risk of bias’, US medical experts warn

The Cass Review into the provision of trans youth healthcare in England and Wales has been criticised in key areas. (Getty)
US experts have claimed that the controversial Cass Report has a “high risk of bias”.
The independent review into the provision of healthcare for trans youngsters has been criticised since it was published last April. Dr Hilary Cass, a paediatric expert, made upwards of 32 recommendations to restructure gender-affirming care in England and Wales.
A number of organisations, including the British Medical Association (BMA), have voiced opposition to the report and accused Cass of ignoring evidence, particularly regarding puberty blockers.
Now, a report published in the New England Journal of Medicine, written by law professors Daniel G Aaron, who is also and MD, and Craig Konnoth, has raised concerns over the review’s methodology, claiming it was “not verified by experts”.

Published on 15 January, the new report, which analysed the Cass from a law and policy perspective, claimed that it “departed from standard practice… [and] deviates from pharmaceutical regulatory standards” while making recommendations that are “not applied elsewhere in paediatric medicine”.
The two professors went on to say: “Indeed… if the US government issued a report in a similar manner, it would be violating federal law… We know Cass chaired the review, but observers must speculate about who else participated in the manuscript’s drafting.”
That lack of clarification means readers will speculate about whether any other authors held a bias against LGBTQ+ people, Aaron and Konnoth said.

“The review’s departure from the evidentiary and procedural standards of medical law, policy and practice can be understood best in the context of the history of leveraging medicine to police gender norms. Recent efforts to increase the presence of women in medicine, improve access to reproductive service and offer [gender-affirming care] seek to break from that history, but the Cass Review represents a return to the past.”
The criticisms echo those made by medical bodies that have already accused Cass of a “selective and inconsistent use of evidence”.
The World Professional Association for Transgender Health, which the Cass Report dismissed as a “poor quality” source of information, accused officials of “intentionally and explicitly excluding any oversight from patients and their families and trans healthcare experts”.
The BMA, which represents more than 190,000 doctors, scrutinised the review and announced an evaluation by a “task and finish” group into its findings.
Health secretary Wes Streeting has continued to implement a ban on puberty blockers for transgender youngsters in England and Wales, using the Cass Review as justification despite the concerns.
Speaking to PinkNews, a spokesperson for the Department of Health and Social care said it believed the report to be “simply wrong.”
“The independent Cass Review is the most comprehensive assessment of gender incongruence in children and young people to date. Its findings and conclusions are robust, backed by clinicians and firmly grounded in evidence and wider research.
“It is supported by the independent Commission on Human Medicines which recently found that the current prescribing and care pathway for gender dysphoria and incongruence presents an unacceptable safety risk for children and young people,” they continued. “Children’s healthcare must always be led by evidence and NHS England is implementing Dr Cass’s recommendations so that children and young people get the safe, holistic care and support they need.”
Evidence from a 2024 independent study in Australia found that puberty blockers are not only widely beneficial for trans youngsters, but their effects can be reversed.
Another study published in October last year found that 97 per cent of patients in the US and Canada were “highly satisfied” with the results.
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