Two pigmented lesions

Correct answer: A. Oral melanotic macule

• A. CORRECT. The ORAL MELANOTIC MACULE is defined precisely this way: increased melanin deposition within the BASAL CELL LAYER with a NORMAL number of melanocytes and no melanocytic proliferation. It is flat, well-demarcated, uniformly brown, usually under 1 cm, and commonest on the vermilion of the lower lip, then gingiva, palate and buccal mucosa. It is benign and does not enlarge — Patient A.
• B. A melanocytic NEVUS is defined by a PROLIFERATION of nevus cells forming NESTS — at the epithelial-connective tissue junction (junctional), within the connective tissue (intramucosal, the commonest oral type), or both (compound). It is a cellular proliferation, not simply increased pigment, and it is more often slightly raised than flat.
• C. ORAL MELANOMA is a malignant proliferation of ATYPICAL melanocytes that invade the underlying connective tissue. It is rare but carries a poor prognosis, favours the HARD PALATE and MAXILLARY GINGIVA, and is characteristically irregular, asymmetrical, variably pigmented and enlarging — the description of Patient B.
• D. SMOKER'S MELANOSIS also involves increased basal melanin, and it is the closest competitor for that reason — but it is DIFFUSE rather than a discrete macule, occurs in a smoker, favours the anterior labial gingiva, and typically fades over months to years after cessation. The melanin production is a protective response to tobacco constituents.

Note: ⚠️ The recall author chose melanoma and recorded uncertainty. ‘A lesion of the basal epithelial cells’ is the textbook description of the MELANOTIC MACULE, so that is how the item is keyed — but note the clinical rule that outranks the histology question: any oral pigmented lesion that is NEW in an adult, ENLARGING, IRREGULAR, or located on the HARD PALATE or MAXILLARY GINGIVA should be biopsied, because oral melanoma is the diagnosis that cannot be missed. Patient A needs reassurance; Patient B needs a biopsy.