Answer: A. Pigmented basal cell carcinoma

Basal cell carcinoma (BCC) is a common form of skin cancer, usually seen in the middle age and elderly patients. They occur most often on light-exposed sites, especially around nose and inner canthus of eyelids, but occasionally may be present on trunk and limbs. They are locally invasive. They grow slowly but relentlessly. A lesion is often present for two or more years before the patient seeks advice. Pigmented BCC is a form of nodular BCC, and is the most common form of BCC seen in Chinese patients. It presents as a dark blue papule or nodule, with a smooth shiny "pearly" surface, sometimes with central ulceration. It is an important differential diagnosis of pigmented lesions in Chinese population.

Superficial spreading melanoma has an asymmetrical, irregular or ill-defined border, variegated colour of brown, black, gray or pink, diameter larger than 6mm, and elevation with surface distortion. Nodular BCC arises quite rapidly within months from normal skin as they lack preceding horizontal growth phase of a superficial spreading melanoma. Biopsy will be necessary to definitively delineate nodular melanoma from pigmented BCC.

Melanocytic naevus usually has an onset in the second to fourth decade of life. Seborrhoeic keratosis presents as darkly pigmented warty nodules with a "stuck on" appearance.