Formestane Endogenous Research Raises Integrity Questions in Australian Horse Racing
Key Insights
A UK study presented at ICRAV 2026 found formestane in 92 of 136 randomly selected horse urine samples, suggesting the breast cancer (search) drug may be produced endogenously by horses.
Racing Victoria (search) has commissioned a 12-month study with RASL to determine if formestane and its metabolites occur naturally at low levels in racehorses, which could lead to a testing threshold.
Twenty-four positive tests have been detected across Victoria, Tasmania, and South Australia from over 40,000 samples, with trainers facing fines and 12-month horse suspensions under strict liability rules.
A growing controversy in Australian horse racing has emerged after breakthrough research suggested that formestane, a prohibited breast cancer (search) drug, may be produced naturally by horses, raising significant questions about the integrity of disciplinary actions taken against multiple trainers.
The UK-based study, commissioned by the British Horseracing Association (search), found formestane "for the first time" in 92 urine samples of 136 horses — comprising 50 geldings, 50 mares, and 36 colts selected at random — raising the possibility the substance was endogenous. Research scientist Marjaana Viljanto presented the findings at the International Conference of Racing Analysts and Veterinarians 2026 (ICRAV 2026) in Melbourne on March 24, an event hosted by Racing Analytical Service Limited (search) (RASL), the same Melbourne lab that detected the formestane positives.
The research has not yet been published or peer-reviewed — a process that can take 12 months — and its conclusions remain unvalidated.
Scale of the Positives
RASL began screening for formestane in 2017 and did not detect a positive until February 2023. Since then, 24 positives have been identified from more than 40,000 samples across thoroughbred and harness racing in Victoria, Tasmania, and South Australia. In Victoria alone, 13 horses have tested positive since the first sample was detected.
Formestane is used to treat breast cancer (search) overseas, primarily in postmenopausal women. It is not imported for human or animal use in Australia. The substance is prohibited in racehorses because it increases levels of testosterone. Both 4-hydroxytestosterone and 6a-hydroxyandrostenedione (search), metabolites also detected in some samples, are anabolic androgenic steroids.
Disciplinary Actions and Industry Response
Trainers from five Victorian stables — Smiley Chan, Julius Sandhu, Symon Wilde, Mark and Levi Kavanagh, and Ash and Amy Yargi — were fined $24,000 (with $12,000 suspended) by the Victorian Racing Tribunal after their horses presented on race day with formestane in their systems. Their runners were suspended for 12 months.
Subsequently, Racing Victoria (search) stewards announced charges against trainers from another six stables: Matthew Brown, Adam Chambers, Nathan Dunn, Lee and Shannon Hope, Lloyd Kennewell, and Paul Preusker. Their horses returned positive urine swabs to formestane, 4-hydroxytestosterone, and 6a-hydroxyandrostenedione (search) between April 14 and November 22 last year. All six horses have been banned for 12 months and their winning prizemoney forfeited.
Under the rules of racing, presentation offences are strict liability offences — Racing Victoria (search) does not have to demonstrate how the substance came to be in the horse, only that it was present. No evidence of formestane was found at any of the charged trainers' stables.
Trainer and Owner Concerns
Two owners wrote to Racing Minister Anthony Carbines in February calling for ministerial intervention, citing "a lack of scientific rigour in investigations." One of the owners, Louise Bryant, part-owner of positive horse Sirileo Miss, along with another unnamed owner, claimed the increasing number of positives "reflects systemic failures in investigation, scientific rigor, and regulatory decision-making by Racing Victoria (search) limited and associated bodies."
The owners warned of "potentially catastrophic consequences for the industry's integrity, international reputation, and public confidence."
Trainer John Hickmott, 82, who was fined $4,000 and had his horse Classy Kenny banned for 12 months after a positive urine sample at Morphettville races on August 16 last year, is threatening to take his case to the High Court. "I have said all along, I took my horse to the races clean, and brought him home clean. What happened to the swab after that, I don't know," Hickmott said.
Regulatory Response
Racing Victoria (search) announced in May it had commissioned a study with RASL to determine if formestane and its metabolites occur naturally at low levels in racehorses. The study will take at least 12 months. If the substances were found to be endogenous, a Racing Victoria spokesperson said, "it would most likely require a change to the national rules and a threshold to be implemented if attainable."
Integrity Commissioner Terrie Benfield, to whom Carbines referred the owners' complaints, stated she did not have the powers to investigate matters within the jurisdiction of courts or tribunals. Benfield noted that racing's controlling bodies "are responsible for establishing integrity standards and rules" and that Racing Victoria (search) had "belatedly" provided owners "with an opportunity to be heard."
A Victorian government spokesperson said it was "appropriate that Racing Victoria (search) and the Integrity Commissioner can conduct their investigations independently of government."
Racing Victoria (search) has strongly refuted suggestions of inappropriate handling: "We strongly refute any suggestion that our stewards have acted inappropriately in their handling of cases involving formestane and its associated substances. All cases have been handled in accordance with the Australian Rules of Racing based on the information available to the stewards at the time."
Guilty findings are rarely overturned, as the Australian Rules of Racing are generally not retrospective.