Tuesday, November 4, 2008

Merkel Cell Carcinoma

Merkel Cell Carcinoma

MD Anderson Cancer Center

Merkel Cell Carcinoma

Merkel Cell Carcinoma (MCC) is a rare skin malignancy which was first described in 1972 by Cyril Toker. However, the name Merkel cell comes from the anatomist who discovered the normal Merkel cell in pig snouts - Friedreich Sigmund Merkel in 1875. Because of the tumor cell characteristics seen under the microscope, the name neuroendocrine carcinoma of the skin is used synonymously with Merkel cell carcinoma.

The true incidence of this cancer is not known, but 400 - 600 cases have been described in the literature. Merkel cell carcinoma is almost exclusively seen in Caucasian people, and most are more than 65 years old. Some of the literature reports that MCC affects men and women equally, but other studies have shown a male predominance. The etiology of this tumor is not clearly defined, but there has been association of MCC to sun exposure. Many of the patients have a history of other basal or squamous cell cancers of the skin, and approximately 10% of the patients will develop a second primary cancer.

Merkel cell carcinoma most commonly occurs in the skin of the head and neck (50%), followed by the extremities and the trunk. The head and neck, cheek, forehead, temple, nose, and upper neck are the most common sites. This tumor is innocuous in appearance - described as a painless, solitary, raised, pink nodule. Most tumors are less than 2 cm when initially discovered. Biopsy is the only way to diagnose MCC. However, the diagnosis is difficult for most pathologists, and requires both the use of the electron microscope and special staining of the cells to differentiate it from other small cell carcinomas.

Merkel cell carcinoma is a very aggressive cancer. Lymph node metastasis occurs early and often. Some studies report palpable lymph nodes at presentation in 45% of patients. However, distant metastasis is rare at presentation. Local and regional recurrence occurs frequently, and is felt to be related to the adequacy of the initial therapy. Distant metastasis occurs in approximately 25% of patients, regardless of therapy.

The current thoughts on treating Merkel cell cancer include both the primary lesion and the regional lymphatics. It is felt that the primary cancer should be surgically removed with negative margins. Studies have shown that surgical treatment alone has a higher rate of local and regional recurrence that those who receive surgical excision and radiation therapy. Thus, after the tumor is removed, 6 weeks of radiation to the surgical site and to the regional lymphatics is recommended. However, despite this aggressive therapy, approximately 40% still develop locoregional recurrence.

It is felt that regardless of therapy, 25 - 35% of patients may ultimately recur. It is felt that the development of locoregional recurrence is a predictor of multiple recurrence and distant metastasis. Thus, it is implied that early locoregional treatment will improve tumor control. However, it is not proven whether locoregional control will affect the rate of distant metastasis and ultimately affect survival.