Case Presentation - Winter, 2010

Merkel Cell Carcinoma

NOTE: The diagnosis and analysis for this case study were provided by an independent physician. All conclusions and opinions are those of the physician and not Hologic, Inc.

History: 87 year old male, previous history of Merkel Cell Carcinoma located on the face

Specimen type: Neck FNA

Case provided by: Oklahoma VA Hospital

Merkel cells are sometimes referred to as neuroendocrine cells. They were first described by Friedrich Sigmund Merkel in 1875 as distinctive small round cells in the basal layer of the epidermis. Merkel Cell Carcinoma is a rare and aggressive form of skin cancer that arises from these neuroendocrine cells in the skin. Approximately 1500 cases of Merkel Cell Carcinoma are diagnosed in the United States per year. Although these carcinomas primarily develop on sun-exposed areas such as the face, neck and arms, they can occur anywhere on the body. This cancer occurs mostly in Caucasian individuals over the age of 65 with a history of extensive sun exposure or immune suppression. Males are twice more likely than females to develop Merkel Cell Carcinoma.

Merkel Cell Carcinomas usually present as painless firm nodules that are red-violet or flesh colored. These cancers grow rapidly and metastasize quickly. They can spread to nearby lymph nodes and to the liver, lungs, brain or bones.

Merkel Cell Carcinoma is a malignant small round blue cell tumor. Tumor cells can be dispersed or form loose clusters. Rosette structures are not uncommon. Scanty cytoplasm and naked nuclei are evident. The nuclei are granular with unremarkable or absent nucleoli. Cytoplasmic inclusions composed of intermediate keratin filaments are a unique morphologic feature of Merkel Cell. The inclusions are round and pink and are located near the nuclei or within nuclear indentations near the nuclei. The presence of indentations in the nuclear membrane can be diagnostically helpful if the cytoplasmic inclusions are not evident.

Differential diagnoses for Merkel Cell Carcinoma include other small round blue cell tumors such as metastatic oat cell carcinoma, lymphoma, melanoma and metastatic carcinoid. Immunohistochemical approaches are used to definitively diagnose Merkel Cell Carcinoma. The intermediate keratin filament inclusions present in Merkel Cell Carcinoma are Cytokeratin 20 positive in a dot-like rim pattern only seen in Merkel Cell and small cell salivary gland carcinoma. Almost all Merkel Cell Carcinomas are positive for neuron specific enolase.

Merkel Cell Carcinoma is an aggressive cancer and is fatal in approximately thirty percent of patients. The tumors are removed by Mohs surgery or wide local excision. Sentinel lymph node biopsy procedure should be performed due to the tendency of this cancer to spread to distant sites and lymph nodes. A full lymph node dissection is usually done if the sentinel lymph node contains cancer. Radiation therapy is given at the site the tumor and sometimes at the draining lymph node area. Chemotherapy is generally reserved for late stages of disease. Merkel Cell Carcinoma will usually have a positive initial response to chemotherapy but often gains resistance. Chemotherapy will generally not cure disease that has metastasized beyond the skin. The 5 year survival rate for Merkel Cell Carcinoma once it has metastasized to the lymph nodes is approximately 50%.

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  4. American Cancer Society