This 85-year-old man was evaluated by his dermatologist for a brown nodule on the right forehead.The tumor measured 0.4 x 0.4 x 0.4 cm in the greatest dimension. No ulcerated or endophytic component was observed. The lesion was removed with a 1.0 cm resection margin, and histology revealed a pigmented basal cell carcinoma. Pigmented basal cell carcinoma is an epithelial tumor wich is more common in darkly pigmented races. It is a variation of nodular basal cell carcinoma. Due to the abundant pigment this lesion is sometimes misdiagnosed as malignant melanoma. The characteristic microscopic features of pigmented basal cell carcinoma are present in this case. They include basaloid tumor cell nests budding from the epidermis into the dermis with variable atypia, retraction artifact (the stroma is separated from tumor nests due to formalin effect during fixation process), peripheral palisading of nuclei on basal layer, presence of mucin within the stroma (might be present within basaloid aggregates), variable amount of melanin and melanocytes within the tumor, variable lymphocytes, plasma cells or lymphoid follicules around the tumor in the dermis. Basal cell carcinoma almost never metastazises. Their biological behavior bears no resemblance to melanoma. Last but not least, this variant of basal cell carcinoma is not among the most aggressive basal cell carcinomas.
There are palisaiding cell layers separated by stroma. The melanin pigment is located within the basaloid cells. Note the "pushing effect" of the tumor on the epidermis which appears thin with orthokeratosis on the stratum corneum.