Lip Carcinoma In Situ — SCE Dermatology MCQ

Correct answer: E — Squamous cell carcinoma in situ (carcinoma in situ of the lip / severe actinic cheilitis)

The correct answer is E, squamous cell carcinoma in situ (carcinoma in situ of the lip, also termed severe actinic cheilitis). Histology showing dysplasia extending through the full thickness of the epithelium with an intact basement membrane defines carcinoma in situ; once the basement membrane is breached this becomes invasive squamous cell carcinoma. On the lip, chronic actinic damage combined with the carcinogenic effect of smoking produces exactly this pattern, clinically presenting as a persistent hyperkeratotic, often fissured or indurated plaque on the vermilion, most commonly the lower lip. This lesion sits on the actinic cheilitis to SCC-in-situ to invasive SCC continuum and, unlike simple hyperkeratosis, requires histological confirmation of full-thickness atypia to make the diagnosis. Why the other options are wrong: C. Mucocele: this is a mucus-filled cyst from a ruptured minor salivary duct, presenting as a soft, fluctuant, translucent swelling, not a hyperkeratotic plaque, and shows no epithelial dysplasia on biopsy. D. Leukoplakia without dysplasia: by definition this is a white patch with no cellular atypia on biopsy, whereas this case explicitly shows severe, full-thickness dysplasia. B. Lichen planus: histology shows a band-like lymphocytic infiltrate, basal cell degeneration and sawtooth rete ridges, not full-thickness epithelial dysplasia, and clinically presents as Wickham striae or erosive lesions rather than a hyperkeratotic plaque. A. Oral candidiasis: this produces removable white plaques with pseudohyphae and yeast on microscopy, with no dysplastic change, and is not linked to smoking-related actinic damage of the lip. Key point: full-thickness epithelial dysplasia with an intact basement membrane equals carcinoma in situ, not invasive cancer, and on the sun-exposed lip this is clinically termed severe actinic cheilitis, warranting active treatment given progression risk to invasive SCC.

Reference: British Association of Dermatologists guidelines for the management of people with cutaneous squamous cell carcinoma in situ (Bowen disease), British Journal of Dermatology 2022;188(2):186-194, https://academic.oup.com/bjd/article/188/2/186/6788751