increased size of the tumor, spreading of the tumor into surrounding and/or distant tissue, and involvement of lymph nodes) is associated with lower survival rates.The National Cancer Data Base has survival rates collected from nearly 3000 MCC patients from year 1996–2000 with 5-year survival rates listed as follows:Stage IA: 80%. Stage IB: 60%. Stage IIA: 60%. Stage IIB: 50%. Stage IIC: 50%. Stage IIIA: 45%. Stage IIIB: 25%. Stage IV:  20%. 5 yr survival may be 51% among people with localized disease, 35% for those with nodal disease, and 14% with metastases to a distant site.Several other features may also affect prognosis, independent of tumor stage. They include MCV viral status, histological features, and immune status. In viral status, MCV large tumor antigen (LT antigen) and retinoblastoma protein (RB protein) expression correlates with more favorable prognosis, while p63 expression correlates with a poorer prognosis. Histological features such as intratumoral CD8+ T lymphocyte infiltration may be associated with a favorable prognosis, while lymphovascular infiltrative pattern may be associated with a poorer prognosis. Immune status, especially T cell immunosuppression (e.g., organ transplant, HIV infection, certain malignancy) predicts poorer prognosis and higher mortality.The antibody titer in the blood to the Merkel cell polyomavirus oncoprotein can be used as a treatment response biomarker in people that have detectable antibodies at the time of diagnosis. Epidemiology
Merkel cell carcinoma occurs most often in Caucasians between 60 and 80 years of age. Its incidence is about twice as high in males as in females.
It is a rare type of skin cancer, with a 2013 incidence of only 0.7 per 100,000 persons in the U.S. As of 2005, roughly 2,500 new cases of MCC are diagnosed each year in the United States, as compared to around 60,000 new cases of malignant melanoma and over 1 million new cases of nonmelanoma skin cancer. Similar to melanoma, the incidence of MCC in the US is increasing rapidly. Worldwide, MCC is most commonly found in regions with increased sun exposure. Australia is the country with the highest incidence of MCC but has a lower incidence of MCV-positive MCC than observed in other countries.Since 2006, it has been known that other primary cancers increase the risk of MCC significantly, especially in those with the prior multiple myeloma, chronic lymphocytic leukemia, and malignant melanoma. Immunosuppression including HIV infection or immunosuppressant therapy following organ transplant or for autoimmune disease can also increase the odds of developing MCC. History
Friedrich Sigmund Merkel (1845–1919) was a German anatomist and histopathologist who first described the Tastzellen (touch cells) in the skin in 1875. In 1878 the term Merkel cell was coined by the anatomist Robert Bonnet (1851–1921). Merkel-cell carcinoma was first described in 1972 by Cyril Toker. He reported five cases of trabecular carcinoma of the skin.