Extramammary Paget disease (EMPD) is a malignant epithelial tumor that most commonly affects the anogenital region and less frequently arises in the axillae. Most cases occur in locations where apocrine glands predominate.1 Few cases of EMPD arising in nonapocrine-bearing regions, or ectopic EMPD, have been reported.2 We describe a case of primary ectopic EMPD with an infiltrative growth pattern arising on the back of a 67-year-old Thai man.
Case Report
A 67-year-old Thai man presented to the dermatology clinic for evaluation of a persistent rash on the right lower back of approximately 30 years’ duration. He reported that the eruption had started out as a small coin-shaped area but had slowly increased in size. Over the last 2 years, the area had grown more rapidly and became pruritic. His medical history was remarkable for hypertension treated with losartan, but he was otherwise healthy. He had no history of cancer or gastrointestinal tract or genitourinary symptoms, and he had no recent fever, weight loss, or night sweats.
On physical examination a well-demarcated, asymmetric, erythematous to brown plaque was noted on the right lower back. The plaque was surfaced by scale and contained a central hyperkeratotic papule (Figure 1). The skin examination was otherwise unremarkable. The patient had no lymphadenopathy.
Figure 1. Ectopic extramammary Paget disease presenting as a well-demarcated, asymmetric, erythematous to brown plaque on the right lower back with associated scale and a central hyperkeratotic papule.
Two punch biopsies were performed. On low power, acanthosis and hyperkeratosis of the epidermis were noted. The epidermis contained a proliferation of large (tumor) cells with pleomorphic nuclei, prominent nucleoli, and abundant pale to clear cytoplasm. The cells were present singularly as well as in clusters and were most prominent along the basal layer but many were also seen extending to more superficial levels of the epidermis (Figure 2A). In one biopsy, the tumor cells were found in the dermis with an infiltrative growth pattern (Figure 2B). Immunohistochemistry (IHC) studies for cytokeratin 7 (Figure 3A and 3B) and carcinoembryonic antigen (Figure 3C) labeled the tumor cells. An IHC study for gross cystic disease fluid protein 15 labeled some of the tumor cells. Immunohistochemistry studies for S-100, human melanoma black 45 (HMB-45), p16, and renal cell carcinoma did not label the tumor cells. An IHC study for MIB-1 labeled many of the tumor cells, indicating a notably increased mitotic index. The patient was diagnosed with ectopic EMPD. He underwent an endoscopy, colonoscopy, and cystoscopy, all of which were normal.
Figure 2. Proliferation of large cells with pleomorphic nuclei, prominent nucleoli, and abundant pale to clear cytoplasm confined to the epidermis in ectopic extramammary Paget disease (A)(H&E, original magnification ×10). The tumor cells demonstrated an infiltrative growth pattern in another biopsy from the plaque (B)(H&E, original magnification ×4).
Figure 3. Immunohistochemical studies for cytokeratin 7 (A and B)(original magnifications ×10 and ×4) and carcinoembryonic antigen labeled the tumor cells strongly and diffusely (C)(original magnification ×10).