Merkel cell carcinoma. Merkel cell carcinoma is a rare malignant cancer that usually begins as a single painless lump on the skin. Merkle cells are highly specialized cells in the epidermis that act as pressure receptors. The origin of Merkle cells is debated and proposed to be derived from neural crest cells or other epidermal cells. Merkel- cell polyoma virus infection, ultraviolet radiation and a weakened immune function probably all contribute to the growth of this cancer.
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