Primary Cutaneous Adnexal Neoplasms and Their Metastatic Look-Alikes

Abstract

Cutaneous adnexal neoplasms can often be confused with other entities, including cutaneous metastases from visceral malignancies. Distinguishing primary cutaneous adnexal neoplasms from metastases is important, as the presence of cutaneous metastases can sometimes be the first sign of an internal malignancy or, more often, can indicate a poor prognosis due to disseminated disease. Primary cutaneous adnexal tumors with clear cell histology such as sebaceous tumors or clear cell hidradenoma can mimic metastatic clear cell renal cell carcinoma. Nonmucinous primary adnexal carcinomas derived from the sweat glands can mimic adenocarcinomas metastatic from the breast, lung, gastrointestinal tract, and elsewhere. Finally, mucinous sweat gland tumors also pose a challenge as they can mimic metastatic mucinous carcinomas, particularly of the breast and gastrointestinal tract. This review includes the morphologic characteristics as well as suggested immunohistochemistry to aid in the distinction of these entities.T he category of cutaneous adnexal neoplasms is a complex one, comprising a large number of closely related entities with eccrine, apocrine, sebaceous, or follicular differentiation. Classification of the adnexal neoplasms can be confusing because they often encompass multiple, sometimes overlapping, lines of differentiation. Furthermore, their diagnosis can be challenging because they morphologically mimic other tumors, including cutaneous metastases of visceral malignancies. This is especially true for strictly intradermal tumors with no epidermal connection and in which a primary cutaneous benign adnexal tumor component is not readily identifiable.Cutaneous metastases have been reported to occur in 0.7% 1 to 9% 2 of patients with visceral tumors. A large retrospective study of patients with carcinoma, specifically excluding melanoma, found cutaneous metastases in 4.7% of these patients. 3 A recent meta-analysis including over 20,000 patients with carcinoma, again excluding melanoma, found the incidence of cutaneous metastases to be 5.3%. 4 Of all cancer patients with metastatic disease, approximately 10% of those metastases were to the skin and in roughly 3 quarters of those patients, the cutaneous metastases were the first sign of extranodal metastases. 5 The most common sites of cutaneous metastases include the abdominal wall and chest, although scalp and neck are less commonly seen. 5-7 This correlates with the observation that cutaneous metastases are most commonly seen in the skin in the region of the primary carcinoma, such as the chest for lung and breast carcinomas and the abdominal wall for gastrointestinal carcinomas. 5 Unusual sites of metastases have been reported including subungual 8 -10 and penis. 11,12 The most common presentation of cutaneous metastases is as a painless nodule, 4,6,7 but metastases to the skin have been reported as bullae, 5 inflammatory carcinoma, 13 zosteriform rashes, 14,15 sclerotic plaques, 15 and mimicking cutaneous vasculitis. 16 The most common primary tumor of cutaneou...

Cutaneous Metastasis: A Study of 138 Cases Diagnosed by Fine-Needle Aspiration Cytology

“…On cytology, the distinction between primary adnexal tumors and cutaneous metastases can be made by morphologic features, histochemical stains, and immunostains. Primary adnexal tumors with a clear cell morphology like sebaceous neoplasms or clear cell hidradenoma can mimic metastatic RCC or a clear cell variant of SCC [25] . Tumor cells showing a PAS-positive diastase-sensitive reaction indicate renal origin.…”