Pagetoid

Overview
Pagetoid is a term used in dermatology to refer to "upward spreading" of melanocytes into the epidermis. It is uncommon and a possible indication of a precancerous or cancerous condition. Cells display pagetoid growth when they invade the upper epidermis from below. Squamous cell carcinoma, melanoma in situ, Pagetoid Bowen disease and other carcinomas can all display pagetoid growth. A pagetoid growth pattern with upward growth of the melanocytes, so they are no longer confined to the basal layer, is considered pathognomonic for melanoma by some pathologists.

Pagetoid melanocytosis refers to the presence of solitary and small groups of melanocytes in the superficial layers of the epidermis. Although it is generally considered to be a diagnostic hallmark of melanoma, it may also be seen in certain melanocytic nevi. Attempts to formulate reliable histological criteria for distinction between benign and malignant pagetoid melanocytosis have been only partly successful. Extensive and diffuse pagetoid spread of melanocytes, especially when it extends laterally beyond the underlying junctional component, combined with marked cytological atypia, favours melanoma. In naevi, pagetoid spread tends to be more limited and there is no marked cytological atypia. Since these criteria are applicable in only a subset of cases, the correct diagnosis of melanocytic lesions must be based not only on the features of pagetoid melanocytosis but also on all histological and clinical findings.