Case 3 Female, 70 years. Irregular pigmented skin lesion, dorsum of footShow diagnosis & comments
Melanoma in situ
Melanoma in situ is hallmarked by the presence of highly atypical melanocytes restricted to the epidermis and epithelial compartment of adnexae (most commonly hair follicles). The atypical melanocytes are located at the dermoepidermal junction as nests and / or lentiginous arrangements (solitary melanocytes lying next to each other and thus replacing most of the basal epidermal keratinocytes). In addition, there is usually spread of the solitary atypical melanocytes into upper parts of the epidermis, including the granular layer and stratum corneum. This phenomenon is known as pagetoid spread, or ascent. The ascending atypical melanocytes in melanoma in situ tend to retain vesicular nuclei and copious cytoplasm, and are also present at the edges of the lesions, where the number of the junctional atypical melanoytes is usually less. This is in contrast to ascent seen in some naevi (Spitz naevus: Reed naevus; acral naevus; traumatized naevus and some others) where ascending naevus cells are generally smaller than junctional ones, and ascent is limited to areas where junctional cellularity is high.
Ascent should not be confused with transepidermal elimination of entire cell nests: this latter phenomenon is seen in some naevi (and melanomas) with many large nests, and has no diagnostic utility.