Histologically, extramammary Paget's disease and mammary Paget's disease (MPD) are characterized by large atypical cells distributed throughout the epidermis. Although classic examples of these disorders are easily diagnosed on morphologic grounds, some cases may cause differential diagnostic problems. Immunohistology with a wide variety of antibodies has been used as an aid for the identification of Paget cells, for their distinction from other entities, and for investigation of the origin or nature of the disorder. Recently, cytokeratin 7 has been proposed as a specific and 100% sensitive marker for Paget's disease. We studied 22 cases of mammary Paget's disease and 22 cases of extramammary Paget's disease with and without an underlying malignancy for their reactivity with monoclonal antibodies to cytokeratin 7 (CK7) and cytokeratin 20 (CK20). Our studies show that anti-CK7 is an effective but not 100% sensitive marker for Paget cells, staining 21 of 22 cases of mammary Paget's disease and 19 of 22 cases of extramammary Paget's disease, whereas CK20 stained 0 of 17 cases of mammary Paget's disease and 6 of 19 cases of extramammary Paget's disease. We also demonstrate that CK7, but not CK20, highlights intraepidermal clear cells with bland nuclear features (Toker cells) that have been reported in 11% of normal nipples. By using CK7 as a marker, however, we were able to identify Toker cells in most of the nipples we studied: 8 of 15 nipples from mastectomy patients without Paget's disease, and 15 of 18 autopsy cases (both male and female) with normal breasts and nipples. It also permitted us to perform more extensive phenotyping on them, showing that Toker cells share similar antigens with Paget cells and with cells lining the underlying normal lactiferous ducts. In 7 of 15 cases containing CK20-positive Merkel cells, CK7 was also seen to stain Merkel cells. In infrequent cases, Toker cells or Merkel cells may be so numerous focally that a CK7 stain may raise the possibility of involvement of the nipple by Paget's disease. An awareness of the CK7 reactivity of Toker cells and Merkel cells as well as attention to the cytologic features of the case should avoid this problem.
Pigmented epithelioid melanocytoma (PEM) is a recently described entity encompassing epithelioid blue nevus (of Carney complex) and most tumors earlier considered as so-called "animal-type melanoma". Loss of expression of a Carney complex gene, cyclic adenosine 3',5' monophosphate-dependent protein kinase regulatory subunit 1alpha, is observed in the majority of PEMs. Initial reports with short-term follow-up have suggested that although PEMs frequently metastasize to lymph nodes, they have a more favorable outcome than conventional melanomas. In this report, we present the results of long-term follow-up in 26 patients with PEMs from North America and Australia. There were 9 males and 17 females, with a median age of 20 years. The tumors involved the trunk (6 cases), extremities (12 cases), genitalia (1 case), and the head and neck region (7 cases) had a median Breslow thickness of 2.2 mm (range 0.80 to 10.0 mm) and a median Clark level of 4. Eight of the patients developed lymph node metastases. After a median follow-up period of 67 months (range 39 to 216 mo), all patients are alive and free of disease. These findings provide further evidence that PEM is a unique low-grade melanocytic tumor with limited metastatic potential (to lymph nodes), but a favorable long-term clinical course.
Acanthosis nigricans is a lesion affecting localized areas of the skin in persons with obesity and/or hyperinsulinemia. Roughening of the skin correlates with histological papilomatosis and the apparent darkening is due to hyperkeratosis. Biochemical mechanisms for developing this hyperplastic lesion are unclear, but likely involve local cutaneous growth factors. Cross sectional surveys of unselected populations have demonstrated that young children have low prevalences of obesity and acanthosis nigricans, but the prevalences of both increase with increasing age until plateaus are reached after the age of ten. Nearly 40% of Native American teenagers have acanthosis nigricans, whereas about 13% of African American, 6% of Hispanic, and less than 1% of white, non-Hispanic children aged 10-19 have clinically apparent acanthosis nigricans. We conclude that the presence of this skin lesion is a clinical surrogate of laboratory-documented hyperinsulinemia. Acanthosis nigricans identifies a subgroup within an ethnic group who have the highest insulin concentration, the most severe insulin resistance, and thus the highest risk for the development of type 2 diabetes.
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