A 76-Year-Old Man With an Eyelid Lesion

Nail Alouch, MD; Doina Ivan, MD; Phyu P. Aung, MD, PhD; Victor G. Prieto, MD, PhD

Disclosures

February 14, 2019

Epidermal involvement by Merkel cell carcinoma is uncommon. It was first noted in 1980 by Sidhu and colleagues.[11]The authors described the presence of the neoplastic cells in the overlying epithelium in two of the seven reported cases. In 1993, Smith and colleagues[2] found the intraepidermal component in 11 of 132 cases (8.3%).[2] Of these 11 cases, only one had pure intraepidermal carcinoma without dermal tumor. The remaining 10 cases had both dermal and epidermal elements. Walsh[6] described the presence of at least focal epidermotropism in eight of 27 cases (30%).

Pure epidermal Merkel cell carcinoma (Merkel cell carcinoma in situ) without a dermal component is exceedingly rare. Most reported patients with pure epidermal Merkel cell carcinoma also had other skin lesions, such as actinic keratosis, squamous cell carcinoma in situ, and trichilemmal cyst.[3,4,12,13,14] Owing to this association, the epidermal component of Merkel cell carcinoma was overlooked or misdiagnosed (usually as squamous cell carcinoma in situ) in some cases.[2]

As mentioned above, Merkel cell carcinoma is aggressive, with a high frequency of metastasis to regional lymph nodes and distant organs. When intraepidermal Merkel cell carcinoma is recognized on skin biopsy, ruling out an invasive component, which can be sometimes minimal, is important. The absence of invasion on a representative biopsy does not establish the diagnosis of pure intraepidermal Merkel cell carcinoma (Merkel cell carcinoma in situ). The rarity of this entity makes it more likely for an intraepithelial lesion to be a nonsampled invasive Merkel cell carcinoma than a pure epidermal Merkel cell carcinoma. Thus, when no invasion is seen on biopsy, examining additional sections to rule out an invasive component is recommended.

Conventional Merkel cell carcinoma is usually treated with wide local excision with potential sentinel lymph node dissection. Owing to the rarity of Merkel cell carcinoma in situ and the possibility of a nonsampled invasive involvement, pure epidermal Merkel cell carcinoma (Merkel cell carcinoma in situ) is usually managed as conventional Merkel cell carcinoma.

The histologic features of Merkel cell carcinoma include small, poorly differentiated round cells with hyperchromatic nuclei, nuclear molding, inconspicuous nucleoli, and scant cytoplasm. The cells can be organized in nests, sheets, and sometimes single cells. Mitotic figures and apoptotic bodies are common. When the tumor is present in the epidermis, the cells demonstrate histologic features similar to those of standard, dermal Merkel cell carcinoma. In addition, the cells may also show pagetoid upward migration of the atypical cells[5,9,12]; Pautrier-like microabscesses[15]; and squamous, glandular, or adnexal differentiation.[3,6]These features are usually seen in other lesions, such as adnexal or squamous cell carcinoma; therefore, recognizing them is important to avoid misdiagnosis.

Histologically, the differential diagnosis for the epidermal Merkel cell carcinoma is broad; it includes such lesions as melanoma in situ, squamous cell carcinoma in situ, Paget disease (mammary and extramammary), sebaceous gland carcinoma, Langerhans cell histiocytosis, and cutaneous T-cell lymphoma. The differential diagnosis also includes benign conditions, such as Toker cell hyperplasia, pagetoid dyskeratosis, and clear cell papulosis (which is an artifactual phenomenon). Immunohistochemical studies are essential in characterizing these lesions and rendering the correct diagnosis.

Immunohistochemically, Merkel cell carcinoma cells typically express neuroendocrine markers, such as synaptophysin, chromogranin, and neuron-specific enolase. The cells also demonstrate the characteristic perinuclear dot-like staining pattern for cytokeratin 20 (in most cases) and pancytokeratin markers, as well as for some of the neuroendocrine markers.

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