White plaques of questionable risk, diagnosed when other known diseases or disorders that carry no risk for oral cancer have been excluded.
Multiple clinical forms exist: homogeneous, speckled, nodular, and verrucous.
May be idiopathic, but is often seen in heavy tobacco users and consumers of alcohol or betel.
The majority are histologically benign; a wide range of histological characteristics can be seen within this category of lesions.
Certain leukoplakias, particularly non-homogeneous leukoplakias, such as speckled leukoplakia and verrucous leukoplakia, have a significant risk of malignant transformation and require frequent and careful follow-up.
Oral leukoplakia, as traditionally defined by the World Health Organization (WHO), is a predominantly white lesion of the oral mucosa that cannot be characterised as any other definable lesion.    Leukoplakia is often associated with tobacco smoking, although idiopathic forms are not rare.   An international working group has amended the earlier WHO definition as follows: "The term leukoplakia should be used to recognise white plaques of questionable risk having excluded (other) known diseases or disorders that carry no risk for cancer". 
Leukoplakias are commonly homogeneous and most are benign. Non-homogeneous leukoplakia - a predominantly white or white and red lesion (erythroleukoplakia) with an irregular texture that may be flat, nodular, exophytic, or papillary/verrucous - is more likely to be potentially malignant. Histological features of both forms of leukoplakia are variable and may include orthokeratosis or parakeratosis of various degrees, mild inflammation, and variable degrees of epithelial dysplasia. However, although criteria for dysplasia have been defined by the WHO, it is difficult to make an objective categorisation of dysplasia owing to a high inter-observer and intra-observer variation in assessment.
Milton J. Dance Jr. Head and Neck Cancer Center
Greater Baltimore Medical Center
JS has delivered testimony as an expert witness in medicolegal cases, chiefly as a defense expert.
We would like to gratefully acknowledge the late Dr Crispian Scully for his contribution to this monograph.
Department of Oral Pathology
School of Dentistry
University of Copenhagen
FP declares that he has no competing interests.
Professor and Head
Department of Oral and Maxillofacial Surgery/Oral Pathology
Vrije Universiteit Medical Center
IVdW declares that he has no competing interests.
Division of Oral Medicine
Department of Dental Diagnostic Science
University of Texas Health Science Center
MH declares that he has no competing interests.
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