Etiology • Unknown, may be related to several factors, as follows:
• Viral—HPV subtypes 11, 13, 24, 33, 57 • Altered expression of cell cycle proteins including cyclin E,
p53, PCNA • Keratinocyte dedifferentiation reflected in deficient
desmoglein production • Immunosuppression • Sun damage
• May represent a highly differentiated form of squamous cell carcinoma
• May indicate underlying alimentary neoplasia (Muir-Torre syndrome)
• Viral—HPV subtypes 11, 13, 24, 33, 57 • Altered expression of cell cycle proteins including cyclin E,
p53, PCNA • Keratinocyte dedifferentiation reflected in deficient
desmoglein production • Immunosuppression • Sun damage
• May represent a highly differentiated form of squamous cell carcinoma
• May indicate underlying alimentary neoplasia (Muir-Torre syndrome)
Clinical Presentation • Usually solitary on sun-exposed areas, including lip • Initially erythematous papule • Rapid growth over 4 to 8 weeks • Nodular, hemispheric, firm nodule • Central keratin core • Occasionally regresses spontaneously • Extremely rare intraorally
Diagnosis • Clinical evaluation, follow-up • Histopathology shows keratin plus normal, peripheral epider-
mis and mature, premature keratinization; no invasion below adnexa; marked pseudoepitheliomatous hyperplasia
Differential Diagnosis • Squamous cell carcinoma • Molluscum contagiosum • Warty dyskeratoma • Verruca vulgaris • Pilomatricoma • Condyloma acuminatum • Squamous papilloma
Treatment • Observation and careful follow-up • Local excision • Cryotherapy • Intralesional chemotherapy (methotrexate, 5-fluorouracil, or
bleomycin)
Prognosis • Excellent