Reevaluation of toluidine blue application as a diagnostic adjunct in the detection of asymptomatic oral squamous carcinoma: a continuing prospective study of oral cancer III.

This study was initiated to evaluate toluidine blue application as a worthwhile and simple diagnostic adjunct to clinical impressions. In an attempt to decrease false positives, a 10--14 day waiting period was initiated to allow inflammatory lesions to resolve before application of stain. Using toluidine blue applications with 235 prospectively documented persistent lesions (105 carcinomas and 130 nonmalignant lesions) resulted in a false negative rate (underdiagnosis) of 6.7% and false positive rate (overdiagnosis) of 8.5%. Using clinical criteria alone resulted in a false negative rate of 4.8% but with a tendency to overdiagnose--28.5% false positives. Combining both diagnostic modalities reduced the false negative rate to 1.9%, i.e., only two of the 105 cancers were not considered significant by toluidine blue stain or clinical impression. This staining technique appears to offer a feasible diagnostic "control" over the subjective impression of the clilnician. Persistent lesions that stain with toluidine blue should be considered carcinoma unless proven otherwise by biopsy.