—  SYMPOSIUM #24  —

Oral Pathology
Moderators: Dr. Antonio Cardesa and Dr. Bruce Wenig

Section 1 - Precancerous Lesions of the Oral Cavity

Nina Gale
Institute of Pathology
University of Ljubljana , Faculty of Medicine
Korytkova 2, 1000 Ljubljana, Slovenia


Introduction
Oral leukoplakia (OL) is worldwide described as the most common premalignant lesion of the oral mucosa. It also remains the most controversial entity of the oral pathology, which has reached a hodgepodge of definitions and interpretations through decades [1, 2, 3]. In 1996, a renewed definition has been proposed stating that OL is a predominantly white lesion of the oral mucosa that cannot be characterized as any other definable lesion; some of leukoplakias will transform into cancer [4]. Although the definition has been most widely accepted, different interpretations continue to appear in textbooks and journals creating a considerable confusion among readers [5]. Analogically, a less frequent lesion, oral erythroplakia (OE), is described as a clinical term defining a red lesion that cannot be identified as another, specific lesion. In spite of all inconsistencies, an important agreement has been recently achieved indicating OL and OE as exclusive clinical entities without specific histopathological connotation. From a biological point of view, the literature abounds with the terms premalignant or precancerous to OL [1, 6, 7]. Both expressions literally imply a transition of OL to invasive cancer. However, the risk of OL to become malignant is relatively low and quite unpredictable. In this direction, the last WHO blue book "Pathology and Genetics of Head and Neck Tumours" has made a considerable step forward in definition of oral precursor lesions underlining that the principal oral and oropharyngeal lesions, including white patches - leukoplakia, red patches - erythroplasia/erythroplasia or mixed red and white lesions, may be precursor lesions. The authors, thus, have willful deleted an obligatory premalignant connotation of these lesions. However, an important caution between red and white lesions has been exposed. Red and mixed lesions (speckled leukoplakia) show a higher frequency of dysplasia, often of high grade. On the other side, the majority of leukoplakias does not undergo malignant change and may even regress particularly if apparent etiologic factors are removed [8].

A transition from normal mucosa to invasive squamous cell carcinoma (SCC) in the mouth and other cavities lined by a squamous epithelium is a comprehensive and multistage process, related to progressive accumulation of genetic changes, which lead to selection of clonal population of transformed epithelial cells [9]. From six to ten independent genetic events are required for progression to SCC. Histological changes of the squamous epithelium that occur in the process of oral carcinogenesis and are clinically designated as OL or OE or mixed lesion, are cumulatively designated squamous intraepithelial lesions (SILs). The term SILs has been proposed as an all embracing expression of the whole spectrum of epithelial changes ranging from squamous cell hyperplasia to carcinoma in situ [10]. Particular interest has been focused on potentially malignant (risky or precursor} lesions [2, 11]. These lesions have been defined as histomorphological changes of the squamous epithelium from which invasive cancer develops in a higher percentage than from other epithelial lesions [10, 11, 12].

Various etiological, clinical, histological and molecular genetic aspects are significant for evaluation, adequate treatment and predictive behavior of SILs, particularly of potentially malignant lesions [10].

Etiology
SILs in the oral cavity are associated with tobacco, whether smoked, chewed or used as snuff, and tobacco seems to be the major carcinogen in the European population [13, 14, 15, 16, 17]. Tobacco is stronger independent risk factor for oral SILs than alcohol [13]. Alcohol has been considered the second most important risk factor for oral and pharyngeal cancer development [15], and its synergistic effect with tobacco is particularly evident [14, 18]. The risk of development of oral dysplasia is increased six to 15 times in smokers and heavy drinkers compared to non-smokers and non-drinkers [7]. The significance of Candida albicans as possible etiological factor of OL remains disputable [19, 20], as does the role of HPV in oral carcinogenesis. The involvement of HPV in initiation and progression of oral malignancy is still matter of debate. Different studies have generated conflicting results concerning the prevalence of HPV, ranging from 0 to 90% [21, 22, 23]. The observed discrepancy may be related to the varying sensitivity of the methodologies applied for HPV detection and epidemiologic factors of the examined patient groups. Recent study on 59 oral SCC showed that occasional findings of HPV DNA (8.4%) may be the result of incidental HPV colonization of the oral mucosa rather than viral infection. In the same study, HPV DNA was detected in 6.6% in the control group of healthy people who matched the subjects with oral SCC in various clinical parameters. HPVs, therefore, probably play a limited role in the etiopathogenesis of the majority of oral SCC [24]. In contrast, SCC of the tonsil seems to be strongly etiologically linked to the HPV infection [10, 25, 26].

Clinical Aspects
OL affects approximately 3% of white adults [27]. It is most frequently seen in middle-aged and older men with increasing prevalence with age, reaching 8% in men over 70 years [28, 29]. The most common sites of OL are buccal and alveolar mucosa and lower lip. Lesions in the floor of the mouth, lateral tongue and lower lip more often show epithelial atypias or even malignant growth [30]. A consensus has been attained to divide OL clinically into homogenous and non-homogenous types [4]. The former is characterized as a uniform, flat, thin lesion with a smooth or wrinkled surface showing shallow cracks, but a constant texture throughout [10]. The latter type is defined as a predominantly white or white-and-red lesion that may be irregularly flat, nodular or exophytic. Nodular lesions have slightly raised rounded, red and/or whitish excrescences. The term non-homogenous is applicable to the aspect of both color (a mixed white and red lesion) and texture (exophytic, papillary or verrucous) of lesions with regard to verrucous lesions; there are no reproducible clinical criteria to distinguish among verrucous hyperplasia, proliferative verrucous hyperplasia and verrucous carcinoma [7]. Any persisting lesion with no apparent etiology should be considered suspicious [31]. A period of 2-4 weeks seems acceptable to observe regression or disappearance of the OL after elimination of possible causative factors. After that time a biopsy is obligatory [7].

Proliferative verrucous hyperplasia (PVL) is a special type of OL with a proven high risk of becoming malignant [32, 33]. Initially, it is a relatively benign looking, homogenous solitary patch, which turns gradually toanexophytic, diffuse or multifocal, progressive, and irreversible lesion [32, 33, 34]. The diagnosis is made retrospectively after evidence of progressive clinical course, accompanied by gradual deterioration of histological changes. Women predominate over men by 4 to 1, with a mean age at diagnosis of 62 years [33]. The epidemiology of PVL does not highlight a particular causal agent and the lesion would appear to be multifactorial [1, 35]. It appears most frequently in the buccal mucosa, followed by gingiva, tongue, and floor of the mouth [33]. The severity of histologic features correlates with duration of the lesion, from a benign keratotic lesion to verrucous hyperplasia, and finally, to one of the three forms of SCC: verrucous, conventional and papillary types [32]. OE is much less common than OL. It occurs most frequently in older men as a red macula or plaque with a soft, velvety texture, quite sharply demarcated and regular in coloration, measuring typically less than 1.5 cm in diameter [36]. There is no sex predilection and it appears most frequent in the 6th and 7th decades [37]. The floor of mouth, ventral and lateral tongue, retromolar region and soft palate are the most frequently involved sites [30, 38]. Although OE is a rare lesion, it is much more likely to show advanced grades of SILs or invasive carcinoma than OL. In all red lesions of the oral mucosa that do not regress within 2 weeks after the removal of possible etiological factors, biopsy is, therefore, mandatory.

Histological Classifications
Worldwide, there are no generally accepted criteria for histological grading system in the head and neck region in relation to severity of SILs and propensity for malignant transformation. The majority of the classifications have followed similar criteria to those in common use for epithelial lesions of the uterine cervix, such as dysplasia or cervical intraepithelial neoplasia systems. World Health Organization (WHO) has recently readopted the dysplasia system for classifying SILs of the oral cavity and larynx [8]. However, due to different standpoints concerning this important problem of oral carcinogenesis, dysplasia system was reviewed simultaneously with two additional classifications: the squamous intraepithelial neoplasia system and the Ljubljana classification [8, 10].

WHO Dysplasia System and the Ljubljana Classification
The altered epithelium shows a variety of architectural and cytological changes that have been grouped under the term dysplasia. The following architectural changes are required to diagnose epithelial dysplasia: irregular epithelial stratification, loss of polarity of basal cells, drop-shaped rete ridges, increased number of mitoses, superficial mitoses, dyskeratosis, and keratin pearls within rete pegs. The cytological abnormalities of dysplasia are: anisonucleosis, nuclear pleomorphism, anisocytosis, cellular pleomorphism, increased nuclear cytoplasmic ratio, atypical mitotic figures, increased number and size of nucleoli, and hyperchromatism.

The dysplasia system includes the following categories: squamous cell hyperplasia, dysplasia with three grades and carcinoma in situ. The week points of this classification can be attributed to the fact that no single combination of the above mentioned histological features allows to consistent distinction between hyperplasia and the earliest grade of dysplasia. Additionally, in dysplasia, which is characterized as a spectrum of histological changes, no criteria exist to precisely divide this spectrum into particular grade [8].

On the other side, the Ljubljana classification was devised to satisfy the specific clinical and histological requirements of the diagnosis of SILs in the region of the upper aerodigestive tract where common etiological, clinical and morphological aspects are found. Briefly, different etiology of SILs in the upper aerodigestive tract in comparison with cervical lesions probably triggers a different pathway of genetic events from those established in cervical lesions. Additionally, different anatomic specificities, various clinical approaches to obtain adequate biopsy specimens as well as different treatment modalities for high risk lesions of cervical and upper aerodigestive tract SILs, were the basis for establishing the Ljubljana classification more than three decades ago and further formulation was performed in 1997 by the Working group on SILs of the European Society of Pathology [10, 12, 39, 40]. The histological system is divided into four grades: simple and basal-parabasal hyperplasias form a benign group, atypical hyperplasia is potentially, and carcinoma in situ is actually a malignant lesion. Opposite to the dysplasia system, detailed criteria for histological grading in the Ljubljana classification, has been proposed [10, 12, 39, 40].

Comparing both classifications, one should be aware that there is no simple relationship and overlapping between the WHO 2005 and the Ljubljana classification. The group of the so-called benign lesions, including squamous and basal-parabasal cell (abnormal) hyperplasia is comparable in both classifications. Disagreement starts with presumption of the WHO 2005 classification that each grade of the whole series of dysplasia is considered to be a precursor or potentially malignant lesion. Histologically, however, there are some similarities between basal and parabasal cell hyperplasia of the Ljubljana classification and mild dysplasia of the WHO 2005 [8]. Mild dysplasia, in contrast to basal and parabasal cell hyperplasia, was classified as the initial grade within a spectrum of potentially malignant group, whereas in the Ljubljana classification, basal-parabasal hyperplasia is considered a benign lesion with minimum risk of malignant transformation. Atypical hyperplasia of the Ljubljana classification is similar to moderate dysplasia, but partially also includes severe dysplasia. The analogy is, thus, only approximate. Carcinoma in situ is equal to carcinoma in situ of the WHO 2005 classification. However, some cases of severe dysplasia would fall into the category of carcinoma in situ according to the Ljubljana classification, and the analogy is again only approximate [10].

Over the many years in practical use, the Ljubljana classification has been found to be more precise for daily diagnostic work than other grading systems and provides data, which have been shown to be closely correlated to the biological behavior of the lesions [12].

Biomarkers Related to Malignant Potential of SILs
The occurrence of the higher grades (moderate and severe dysplasia, atypical hyperplasia) of oral SILs is considered the most important risk of SCC development. The reported frequency of malignant transformation of OL ranges from 3.1% [41] to 17.5% [42]. Several locations of OL, together with histological abnormalities, are linked with higher malignant transformation. The floor of the mouth is, thus, the highest risk site, followed by the tongue and lip [37].

The clinical appearance of non-homogenous or speckled OL may correlate with likelihood that the lesion will show epithelial changes or malignant transformation. Silverman and co-workers reported the overall malignant transformation in 17.5% of patients with OL (homogenous form in only 6.6%, and speckled form in 23.4%) [33]. A special subtype of OL, PVL was found to develop SCC in 70.3% of patients [33]. Compared to OL, OE has significantly worse biological behavior with. Shafer and Waldron reviewed their biopsy experiences with 65 cases of OE: 51% of cases showed invasive SCC, 40% were carcinoma in situ or severe dysplasia, and the remaining 9% were mild to moderate dysplasia [37].

There are no individual markers that reliably predict malignant transformation of oral SILs.

In terms of prognostic value, genetic events such as LOH of 3p, 9p21 and 17q 13 and DNA aneuploidy are considered substantial risk of malignant transformation [10, 43]. Additionally, telomerase reactivation has been shown to be an early event of laryngeal and oral carcinogenesis, already detectable in the stage of atypical hyperplasia in 75% and 43%, respectively. However, for progression towards invasive SCC other genetic events seem to be necessary [44, 45].

In conclusion, we suggest that clinically diagnosed OL should no longer be considered as precursor lesions. Histology obviously remains, together with accurate clinical data, the most relevant predictive factor as long as unfailing molecular marker(s) are available to predict malignant transformation.

References
  1. Suarez P, Batsakis JG, el-Naggar AK (1998) Leukoplakia: still a gallimaufry or is progress being made? A review. Adv Ana t Pathol 5:137-155

  2. Küffer R, Lombardi T (2002) Premalignant lesions of the oral mucosa. A discussion about the place of oral intraepithelial neoplasia (OIN). Oral Oncol 38:125-130

  3. Reibel J (2003) Prognosis of oral pre-malignant lesions: significance of clinical, histopathological, and molecular biological characteristics. Crit Rev Oral Biol Med 14:47-62

  4. Axell T, Pindborg JJ, Smith CJ, van der Waal I (1996) Oral white lesions with special reference to precancerous and tobacco- related lesions: conclusions of an international symposium held in Uppsala , Sweden , May 18-21 1994 . International Collaborative Group on Oral White Lesions. J Oral Pathol Med 25:49-54

  5. Auluck A, Pai KM (2005) (Mis) Interpretation of leukoplakia. J Can Dent Assoc 71:237-238

  6. Waal van der I, Axell T (2002) Oral leukoplakia: a proposal for uniform reporting. Oral Oncol 38:521-526

  7. Waal , van der I, Schepman KP, van der Meij EH, Smeele LE (1997) Oral leukoplakia: a clinicopathological review. Oral Oncol 33:291-301

  8. Gale N, Pilch BZ, Sidransky D, Naggar AEl, Westra W, Califano J, Johnson N, MacDonald DG (2005) Epithelial precursor lesions. In: Barnes L, Eveson JW, Reichart PA, Sidransky D (eds) World Health Organization Classification of Tumours Pathology and genetics of tumours of the head and neck, pp 177-179, IARC, Lyon,

  9. Ha PK, Califano JA (2002) The molecular biology of laryngeal cancer. Otolaryngol Clin North Am 35:993-1012

  10. Gale N, Zidar N (2006) Benign and potentially malignant lesions of the squamous epithelium and squamous cell carcinoma. In: Cardesa A and Slootweg PJ (Eds) Pathology of the Head and Neck, pp 2-38, Springer-Verlag Berlin , Heidelberg

  11. Luna MA, Pineda-Daboin K (2001) Upper aerodigestive tract. In: Henson and Albores-Savedra's Pathology of incipient neoplasia, 3rd ed, pp 57-85, Oxford , New York

  12. Gale N, Kambič V, Michaels L, Cardesa A, Hellquist H, Zidar N, Poljak M (2000) The Ljubljana classification: a practical strategy for the diagnosis of laryngeal precancerous lesions. Adv Anat Pathol7:240-251

  13. Jaber MA, Porter SR, Gilthorpe MS, Bedi R, Scully C (1999) Risk factors for oral epithelial dysplasia-the role of smoking and alcohol. Oral Oncol 35:151-156

  14. Johnson NW, Warnakulasuriy S, Tavassoli M (1996) Hereditary and environmental risk factors; clinical and laboratory risk matters for head and neck, especially oral, cancer and precancer. Eur J Cancer Prev 5:5-17

  15. Moreno-Lopez LA, Esparza-Gomez GC, Gonzalez-Navarro A, Cerero-Lapiedra R, Gonzalez-Hernandez MJ, Dominguez-Rojas V (2000) Risk of oral cancer associated with tobacco smoking, alcohol consumption and oral hygiene: a case-control study in Madrid , Spain . Oral Oncol 36:170-17

  16. Reichart PA (2001) Identification of risk groups for oral precancer and cancer and preventive measures. Clin Oral Investig 5:207-213

  17. Sciubba JJ (1995) Oral leukoplakia. Crit Rev Oral Biol Med 6:147-160

  18. Johnson NW, Ranasinghe AW, Warnakulasuriya KA (1993) Potentially malignant lesions and conditions of the mouth and oropharynx: natural history-cellular and molecular markers of risk. Eur J Cancer Prev 2:31-5

  19. Barrett AW, Kingsmill VJ, Speight PM (1998) The frequency of fungal infection in biopsies of oral mucosal lesions. Oral Dis 4:26-31

  20. Rindum JL, Stenderup A, Holmstrup P (1994) Identification of Candida albicans types related to healthy and pathological oral mucosa. J Oral Pathol Med 23:406-411

  21. Bouda M, Gorgoulis VG, Kastrinakis NG, Giannoudis A, Tsoli E, Danassi-Afentaki D, Foukas P, Kyroudi A, Laskaris G, Herrington CS, Kittas C (2000) "High risk" HPV types are frequently detected in potentially malignant and malignant oral lesions, but not in normal oral mucosa. Mod Pathol 13:644-653

  22. Sugiyama M, Bhawal UK, Dohmen T, Ono S, Miyauchi M, Ishikawa T (2003) Detection of human papillomavirus-16 and HPV-18 DNA in normal, dysplastic, and malignant oral epithelium. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 95:594-600

  23. Young SK, Min KW (1991) In situ DNA hybridization analysis of oral papillomas, leukoplakias, and carcinomas for human papillomavirus. Oral Surg Oral Med Oral Pathol 71:726-729

  24. Kansky AA, Poljak M, Seme K, Kocjan BJ, Gale N, Luzar B, Golouh R (2003) Human papillomavirus DNA in oral squamous cell carcinomas and normal oral mucosa. Acta Virol 47:11-16

  25. El-Mofty SK, Lu DW (2003) Prevalence of human papillomavirus type 16 DNA in squamous cell carcinoma of the palatine tonsil, and not the oral cavity, in young patients: a distinct clinicopathologic and molecular disease entity. Am J Surg Pathol 27:1463-1470

  26. Li W, Thompson CH, O'Brien CJ, McNeil EB, Scolyer RA, Cossart YE, Veness MJ, Walker DM, Morgan GJ, Rose BR (2003) Human papillomavirus positivity predicts favourable outcome for squamous carcinoma of the tonsil. Int J Cancer 106:553-558

  27. Bouquot JE (1994) Oral leukoplakia and erythroplakia: a review and update. Pract Periodontics Aesthet Dent 6:9-17

  28. Bouquot JE, Gnepp DR (1991) Laryngeal precancer: a review of the literature, commentary, and comparison with oral leukoplakia. Head Neck 13:488-497

  29. Bouquot JE, Gorlin RJ (1986) Leukoplakia, lichen planus, and other oral keratoses in 23,616 white Americans over the age of 35 years. Oral Surg Oral Med Oral Pathol 61:373-381

  30. Neville BW, Day TA (2002) Oral cancer and precancerous lesions. CA Cancer J Clin 52:195-215

  31. Mashberg A, Samit A (1995) Early diagnosis of asymptomatic oral and oropharyngeal squamous cancers. CA Cancer J Clin 45:328-351

  32. Batsakis JG, Suarez P, el-Naggar AK (1999) Proliferative verrucous leukoplakia and its related lesions. Oral Oncol 35:354-359

  33. Silverman S Jr, Gorsky M (1997) Proliferative verrucous leukoplakia: a follow-up study

  34. Zakrzewska JM, Lopes V, Speight P, Hopper C (1996) Proliferative verrucous leukoplakia: a report of ten cases. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 82:396-401

  35. Fettig A, Pogrel MA, Silverman S Jr, Bramanti TE, Da Costa M, Regezi JA (2000) Proliferative verrucous leukoplakia of the gingiva. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 90:723-730

  36. Reichart PA, Philipsen HP (2005) Oral erythroplakia – a review. Oral Oncol 41:551-561

  37. Shafer WG, Waldron CA (1975) Erythroplakia of the oral cavity. Cancer 36:1021-1028

  38. Bouquot JE, Ephros H (1995) Erythroplakia: the dangerous red mucosa. Pract Periodontics Aesthet Dent 7:59-67

  39. Hellquist H, Cardesa A, Gale N, Kambič V, Michaels L (1999) Criteria for grading in the Ljubljana classification of epithelial hyperplastic laryngeal lesions. A study by members of the Working group on Epithelial Hyperplastic Laryngeal Lesions of the European Society of Pathology. Histopathology 34:226-233

  40. Michaels L, Hellquist HB (2001) Ear, nose and throat histopathology, 2nd ed, pp 1-551, Springer, London

  41. Waldron CA, Shafer WG (1975) Leukoplakia revisited. A clinicopathologic study3256 oral leukoplakias. Cancer 36: 1386-1392

  42. Silverman S Jr, Gorsky M, Lozada F (1984) Oral leukoplakia and malignant transformation. A follow-up study of 257 patients. Cancer 53:563-568

  43. Sudbo J, Kildal W, Risberg B, Koppang HS, Danielsen HE, Reith A (2001) DNA content as a prognostic marker in patients with oral leukoplakia. N Engl J Med 344:1270-1278

  44. Luzar B, Poljak M, Marin IJ, Eberlinc A, Klopčič U, Gale N (2004) Human telomerase catalytic subunit gene re-expression is an early event in oral carcinogenesis. Histopathology 45:13-19

  45. Luzar B, Poljak M, Marin IJ, Gale N (2003) Telomerase reactivation is an early event in laryngeal carcinogenesis. Mod Pathol 16:841-848