Additionally, they have not been shown to support Merkel-cell polyoma virus infection, which is believed to drive oncogenesis in approximately 80% of MCC.Instead, it has been proposed the MCC may originate from a Merkel cell precursor, at which point it gains features similar to those of Merkel cells. One such precursor is the human fibroblast. Evidence for a fibroblast precursor includes its location in the dermis, which is thought to be the primary site of origin for MCC. Additionally, in vitro experiments have demonstrated that fibroblasts not only support Merkel cell polyomavirus (MCV) infection but can be induced into having a MCC phenotype by the expression of viral proteins.However, others have argued that MCC likely derives from an epithelial precursor cell due to its frequent presence in mixed tumors including epithelial neoplasms such as squamous cell carcinoma. While epithelial cells are not typically found in the dermis, hair follicles include epithelial cells that have been shown to have oncogenic potential, and have therefore been proposed as a possible site for a MCC precursor.Finally, the presence of B-cell surface markers on MCC in addition to the high correlation between MCC and B-cell lymphomatous cancers have also led to suggestions that MCC may share a progenitor with B-cells. Because of the differences in physiology and prognosis between MCV+ and MCV- MCC (see below), however, some have suggested that these two subtypes of MCC may actually derive from different progenitor cells.Several factors are involved in the pathophysiology of MCC, including MCV, ultraviolet radiation (UV) exposure, and weakened immune function.
Merkel cell carcinoma (MCC) is a rare and aggressive skin cancer occurring in about 3 people per 1,000,000 members of the population. It is also known as cutaneous APUDoma, primary neuroendocrine carcinoma of the skin, primary small cell carcinoma of the skin, and trabecular carcinoma of the skin. Factors involved in the development of MCC include the Merkel cell polyomavirus (MCPyV or MCV), a weakened immune system, and exposure to ultraviolet radiation. Merkel-cell carcinoma usually arises on the head, neck, and extremities, as well as in the perianal region and on the eyelid. It is more common in people over 60 years old, Caucasian people, and males. MCC is less common in children. Signs and symptoms
Merkel cell carcinoma (MCC) usually presents as a firm nodule (up to 2 cm diameter) or mass (>2 cm diameter). These flesh-colored, red, or blue tumors typically vary in size from 0.5 cm (less than one-quarter of an inch) to more than 5 cm (2 inches) in diameter and may enlarge rapidly. Tumors can present as painless, tender or itchy, and other MCC manifestations as papules or plaques have also been reported. Although MCC may arise almost anywhere on the body, it is most commonly found in sun-exposed areas such as the head, neck or extremities. Five key attributes of MCC were summarized in 2008 in the acronym AEIOU (Asymptomatic/lack of tenderness, Expanding rapidly, Immune suppression, Older than 50 years, and Ultraviolet-exposed site on a person with fair skin). Ninety percent of MCCs have three or more of those features.