Immunohistology is valuable in distinguishing between Paget's disease, Bowen's disease and superficial spreading malignant melanoma.

Thirty-nine lesions, originally diagnosed as Paget's disease (19), superficial spreading melanoma (13) or Bowen's disease (7), were reviewed. Supplementary immunohistochemistry on routine processed tissue, using antibodies to cytokeratins (PKK1 and M717) and to S-100 protein, was carried out. Two of the lesions, originally classified as Bowen's disease and superficial spreading type malignant melanoma respectively, were reclassified as Paget's disease based on the immunohistochemical findings. Both lesions contained pagetoid cells positive with PKK1. The results indicate that immunohistochemistry may sometimes be valuable in establishing the correct diagnosis in such lesions.