Oral cancer (OSCC – oral squamous cell carcinoma) often occurs after a condition called PMD (potentially malignant disorder), which can sometimes progress to cancer. If conditions such as oral cancer or PMD are identified early enough, outcomes for patients can be improved. The current method of diagnosing cancer of the mouth or lips involves the surgical removal of a piece of affected tissue that is sent to a laboratory for histological examination using a microscope (scalpel biopsy). This is painful for patients and involves a delay. The aim of this review was to find out the accuracy of three alternative diagnostic tests that are less invasive and provide more timely results.
What was the research?
A systematic review of diagnostic test accuracy studies to find out which test is the most accurate way to diagnose potentially malignant disorders which could progress to oral cancer.
Who conducted the research?
The research was conducted by a team led by Richard Macey from the University of Manchester, on behalf of the Cochrane Oral Health Group. Tanya Walsh, Paul Brocklehurst, Alexander R. Kerr, Joseph LY Liu, Mark W Lingen, Graham R Ogden, Saman Warnakulasuriya and Crispian Scully were also on the team.
What evidence was included in the review?
Forty-one studies involving 4002 participants, published between 1980 and 2012, were included. Each participant underwent one of three diagnostic tests for oral cancer and PMD as well as the standard method of diagnosis by surgical biopsy. By comparing results, the researchers were able to evaluate the accuracy of each test as compared to surgical biopsy.
Three tests (index tests) were evaluated.
1. Vital stain – a liquid that can be used as a mouthrinse or applied straight on to a suspected area of the mouth. It is thought that any area that is coloured blue after rinsing with water has a high chance of being oral cancer or PMD.
2. Oral cytology – instead of using a scalpel to cut away a piece of the suspected area, a brush is used to remove cells that are sent to a laboratory for examination under a microscope.
3. Light-based detection – a special light shone in the mouth that is believed to make cancerous areas appear different to healthy areas.
There were no eligible studies that looked at the accuracy of tests of blood or saliva.
What did the evidence say?
The proportion of people with OSCC or PMD identified through surgical biopsy varied in the included studies. We used the middle value for the included studies to illustrate the implications of the different tests. A false negative result means that people that truly have oral cancer or PMD will be diagnosed as free from the condition, possibly to be correctly diagnosed at a later date when the condition will be more difficult to treat successfully. A false positive result would mean that people who did not truly have PMD or oral cancer would be diagnosed as having it and therefore unnecessarily undergo invasive treatment.
If vital staining was used to identify OSCC or PMD in a sample of 1000 people (of whom 500 truly have OSCC or PMD), then the condition would go undetected in 80 people (false negative result) and 150 people without the condition would be told they have the condition (false positive result). If cytology was used, the condition would go undetected in 45 people and 45 people without the condition would be told they have the condition. If a light-based detection method was used, the condition would go undetected in 45 people and 210 people without the condition would told they have the condition.
Therefore, in terms of correctly classifying people, cytology was the most accurate of the three tests.
How good was the evidence?
There were shortcomings in many of the studies that put them at high risk of bias and so the key results should be interpreted with caution. The main concern was the ways in which people were selected to take part in the studies. When patients at particularly high or low risk of oral cancer are selected to participate then this can influence the results of the study. Additionally, there were studies where the results from the standard method of diagnosis (‘index test’) were not reported and the reasons for this were not explained.
None of the tests evaluated in this review that were additional to a visual examination can be recommended as a replacement for the currently used standard of a scalpel biopsy and histological assessment.
Macey R, Walsh T, Brocklehurst P, Kerr AR, Liu JLY, Lingen MW, Ogden GR, Warnakulasuriya S, Scully C. Diagnostic tests for oral cancer and potentially malignant disorders in patients presenting with clinically evident lesions. Cochrane Database of Systematic Reviews 2015 , Issue 5 . Art. No.: CD010276. DOI: 10.1002/14651858.CD010276.pub2 .