Cutaneous decidualized endometriosis. A pseudomalignancy.

Mistaking a benign neoplasm for a malignant one is usually the result of the benign neoplasm having cytologic atypia or of normal tissue of one organ being present ectopically in another. In some instances the pathologist is simply not familiar with the lesion. A case of decidualized cutaneous endometriosis is described in which the histologic features included cytologic atypia, circumscription of epithelial nodules, glandular spaces, mononuclear cells within the around the endometrial nodules, and no mitoses. This histologic pseudomalignancy is not common and can be misinterpreted as metastatic is not common and can be misinterpreted as metastatic malignancy by dermatopathologists not familiar with gynecologic pathology.