Oral Cavity Leukoplakia

Oral cavity leukoplakia:
- Is a clinical diagnosis defined by the WHO as:
  - A “white plaque of questionable risk having excluded other known diseases or disorders that carry no increased risk for cancer”
It is the most common oral potentially malignant disorder (OPMD) in North America and Europe:
- With a prevalence ranging from 0.1% to 33%
Definition:
- Oral leukoplakia (OL) is a predominantly white patch or plaque on the oral mucosa:
  - That cannot be characterized clinically or pathologically as any other disorder
- It is a diagnosis of exclusion:
  - Conditions such as:
    - Frictional keratosis, lichen planus, candidiasis, and other identifiable white lesions must be ruled out before the term is applied
- A final diagnosis of leukoplakia in cases with an identifiable causative factor (e.g., friction, tobacco):
  - Can only be made in retrospect after failure to resolve within 4 to 8 weeks of eliminating the suspected cause
Pathophysiology:
- Leukoplakia represents a spectrum of epithelial alterations:
  - Driven by accumulating somatic – genomic alterations
- The molecular progression model involves:
  - Sequential loss of heterozygosity (LOH) at specific chromosomal loci:
    - Early losses at 9p21 (p16 inactivation) and 3p21, followed by 17p13 (p53 mutation), 11q13 (cyclin D1 amplification), and later losses at 4q, 8p, 13q, and 14q
  - Tumor progression from OL:
    - OIs promoted by somatic genomic alterations, immune evasion, and abrogation of effective immune responses against cancer cells
  - Overexpression of p53 and deletions /mutations in KMT2C, p16INK4a, and p14ARF genes have been identified:
    - Particularly in proliferative verrucous leukoplakia (PVL)
  - Microbial dysbiosis:
    - May also contribute to a chronic inflammatory microenvironment favoring epithelial transformation
Etiology and Risk Factors:
- Tobacco and alcohol consumption:
  - Are the most common risk factors
- However, OL can also occur in non-smokers — notably:
  - Most patients with PVL have never smoked:
    - Yet PVL carries the highest malignant transformation rates (70% to 100%)
- Additional risk factors include:
  - Betel quid / areca nut use
  - Immunosuppression:
    - HIV-positive patients with OL are more likely to develop oral cancer
Clinical Presentation:
- OL typically presents as:
  - A white, adherent plaque that cannot be scraped off:
    - Lesions are largely asymptomatic
- Two clinical subtypes are recognized:
  - Homogeneous leukoplakia:
    - Uniformly white, flat, thin plaques with a smooth or slightly wrinkled surface
    - These carry a lower risk of malignant transformation
  - Nonhomogeneous leukoplakia:
    - Mixed red-and-white lesions (erythroleukoplakia), nodular, verrucous, or speckled variants
    - These carry a significantly higher risk of malignant transformation
- Common sites include:
  - The lateral / ventral tongue, floor of mouth, soft palate, buccal mucosa, and gingiva
- Proliferative verrucous leukoplakia (PVL):
  - A distinct aggressive subtype, is characterized by multifocal keratotic plaques with progressive expansion, high recurrence, and strong malignant potential
Histology:
- Histopathology of leukoplakia can reveal a range of findings:
  - Hyperkeratosis (orthokeratosis or parakeratosis) without dysplasia:
    - The most common finding:
      - Represents benign epithelial thickening
  - Epithelial dysplasia:
    - Classified as:
      - Mild, moderate, or severe
    - Characterized by:
      - Architectural disturbance with blunt rete pegs, increased basal layer width, dyskeratosis (premature individual cell keratinization), nuclear enlargement, pleomorphism, hyperchromasia, and increased / atypical mitoses
  - Carcinoma in situ or invasive squamous cell carcinoma:
    - May be found on biopsy of clinically apparent leukoplakia
    - Importantly, frank dysplasia is more frequently found in isolated (unifocal) leukoplakia than in PVL:
      - Yet PVL has a much higher malignant transformation rate (~ 50% vs. ~ 9.5%), underscoring that histologic grade alone does not fully predict risk
Management:
- Management is guided by histopathologic findings and clinical risk factors:
  - All leukoplakias should be biopsied regardless of clinical impression:
    - As the decision to biopsy based on visual assessment alone has low sensitivity (59.6%) and low specificity (62.1%) for identifying cancer
  - Benign (no dysplasia):
    - Active surveillance with periodic clinical examination, or treatment with topical therapy
    - Risk factor modification (tobacco and alcohol cessation) is essential
  - Dysplastic lesions:
    - Surgical excision:
      - Scalpel or laser ablation – is the standard approach
      - CO₂ laser ablation and photodynamic therapy have also been used
    - Chemoprevention:
      - Vitamin A, retinoids, beta-carotene, and lycopene have shown some short-term efficacy in clinical resolution of lesions but no treatment has been proven to prevent long-term malignant transformation in RCTs
      - Relapses and adverse effects are common
- Close follow-up is mandatory regardless of treatment, as recurrence rates are high (37.5% in one series) and malignant transformation can occur even after complete excision:
  - The American Dental Association (2026) recommends routine clinical oral examination for all adults, including systematic visual inspection and palpation to detect OPMDs early
Prognosis and Malignant Transformation:
- The mean malignant transformation rate of OL is approximately:
  - 3.5% (range 0.13% to 34%) across studies:
    - With an estimated annual rate of ~1.5% to 2% per year
- A large population-based cohort study (n = 4,886) found a 5-year absolute risk of oral cancer of 3.3% overall, stratified by dysplasia grade:
  - No dysplasia: 2.2%
  - Mild dysplasia: 11.9%
  - Moderate dysplasia: 8.7%
  - Severe dysplasia: 32.2%
- Critically, 39.6% of cancers arose from biopsied leukoplakias without dysplasia:
  - Highlighting that absence of dysplasia does not eliminate risk
- Risk factors for malignant transformation include:
  - Female sex
  - Lesion area > 200 mm²
  - Epithelial dysplasia
  - Nonhomogeneous type
  - Tongue location
  - Immunosuppression
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