People with suspected mouth cancer are having their diagnosis delayed because they are first referred to a dentist, surgeons have warned.
Guidance from the National Institute for Health and Care Excellence (Nice) says people with a lump in their mouth or who have a red or white patch in their mouth should be sent for "assessment for possible oral cancer by a dentist" within two weeks of seeing their GP.
But experts warn that this can slow down the process for diagnosing people with cancer, and say they should see a hospital specialist within two weeks.
Writing in the British Journal of Oral and Maxillofacial Surgery (BJOMS), they said around one in nine patients could have their diagnosis delayed due to the current guidance, which was updated in 2015 following earlier guidance in 2005.
The experts reviewed 91 referrals, of whom six patients were subsequently diagnosed with cancer.
Nine referrals would have gone to a dentist first, of whom one patient was eventually diagnosed with cancer.
Lead author, and British Association of Oral and Maxillofacial Surgeons (BAOMS) fellow in training, David Grimes said the Nice guidance "may expose patients to increased risk of delayed referral because there is no clear referral pathway between doctors and dentists for suspected cancer".
As a consequence, some people may suffer delays in having their cancer diagnosed.
He said an earlier audit found that half of the mouth cancer cases were diagnosed at an advanced stage.
Co-author Jaymit Patel said: "When we saw the most recent guidelines we were concerned about the recommendation for GPs to refer some patients directly to dentists when no agreed pathway exists.
"We considered that this could lead to a delay in the review of the patient's case by an appropriately trained professional, so we decided to audit our caseload to see what the effect might be."
Mike Bater, from the BAOMS, said the organisation had raised concerns with Nice regarding the changes in referrals several months ago.
"This paper demonstrates that changes in the pathway introduce an avoidable delay in patient referral, potentially leading to a compromise in treatment success.
"We know that patients with mouth cancer are more likely to be cured if the disease is diagnosed at an early stage, and also that the morbidity (side-effects) from treatment increase if the diagnosis is made late."
More than 7,500 cases of mouth cancer are diagnosed in the UK each year and more than 2,300 people die from the disease.
A Nice spokesman said: "There is no evidence that our 2015 suspected cancer guidance is leading to a delay in diagnosis; these concerns are premature and unproven.
"We would be happy to consider evidence which shows a clear effect on the stage of cancer at diagnosis, but our expectation is that the guidance will result in earlier diagnosis, not later."