Excerpt from Wikipedia:

 Merkel cell cancer, also called Merkel cell carcinoma, trabecular cancer, Apudoma of skin, or Small cell neuroepithelial tumor of the skin, is a rare and highly aggressive cancer where malignant cancer cells develop on or just beneath the skin and in hair follicles. This cancer is a type of neuroendocrine tumor, like small cell lung cancer. Once it has metastasized to the lymph nodes, the 5-year survival rate for a patient is about 50 percent. A small tumor (less than 2 cm) that has not metastasized to the lymph nodes reported a 5-year survival rate of more than 90 percent; however, at the time of diagnosis of MCC the 5-year survival was 64 percent. Up to half of patients suffer a recurrence.^[1]

It occurs most often on the face, head, and neck. It usually appears as firm, painless, nodules, or tumors. These flesh-colored, red, or blue tumors vary in size from 5 mm (less than a quarter of an inch) to more than 5cm (2 inches). The tumor grows rapidly. About half of all Merkel cell cancers occur on the sun-exposed areas of the head and neck, while one-third begin on the legs, and 15% occur on the arms. The cancer may also begin on other parts of the body, such as the trunk.

From initial onset, Merkel cell cancer metastasizes quickly and spreads to other parts of the body, tending towards the regional lymph nodes. The tumor tends to invade underlying subcutaneous fat, fascia, and muscle. It can also metastasize to the liver, lungs, brain or bones.

More information can be found on the following links:

http://en.wikipedia.org/wiki/Merkel_cell_carcinoma