The differential diagnosis of pagetoid cells in the epidermis.

In addition to Paget's disease, a heterogeneous group of processes with diverse histogeneses can give rise to intraepidermal pagetoid cells. These diseases share as their common denominator the presence of discrete non-Malpighian or abnormal Malpighian cells occurring singly or in nests within the epidermis. Either Pagetoid cells can represent the only histologic change, as in pagetoid squamous cell carcinoma in situ or superficial spreading malignant melanoma in situ, or they can be an expression of an associated dermal or internal malignancy, as in sebaceous carcinoma or breast carcinoma. The histologic appearance of the pagetoid cells in these diverse disorders can be quite similar, rendering the differential diagnosis difficult. A review of the entities that enter into the differential diagnosis of intraepidermal pagetoid cells is presented, emphasizing their distinguishing histologic and immunophenotypic features and differential diagnosis.