MCC is sometimes mistaken for other histological types of cancer, including basal cell carcinoma, squamous cell carcinoma, malignant melanoma, lymphoma, and small cell carcinoma, or as a benign cyst. Merkel cell carcinomas have been described in children, however pediatric cases are very rare.Merkel-cell cancers tend to invade locally, infiltrating the underlying subcutaneous fat, fascia, and muscle, and typically metastasize early in their natural history, most often to the regional lymph nodes. MCCs also spread aggressively through the blood vessels to many organs, particularly to liver, lung, brain, and bone. Pathophysiology
Cell of origin
Although MCC was initially named for the Merkel cell due to histologic and physiologic similarities between MCC and Merkel cells, the cellular progenitor of MCC has been a heavily debated question. Merkel cells are highly specialized cells that act as pressure receptors in the epidermis. The origin of Merkel cells themselves is debated and proposed to be derived from neural crest cells or epidermal progenitors. MCC is similar to Merkel cells in its histological appearance (see below: Diagnosis) and shares many immunohistochemical markers with Merkel cells, including epidermal marker cytokeratin 20 and neuroendocrine markers synaptophysin and chromogranin A. Furthermore, the ion channel Piezo2 and transcription factor Atoh1, both specific to Merkel cells, are also expressed by MCC. However, Merkel cells are post-mitotic cells with a low probability of cancerous transformation.
Onset may refer to:

Onset (audio), the beginning of a musical note or sound
Onset, Massachusetts, village in the United States
Onset Island (Massachusetts), a small island located at the western end of the Cape Cod Canal
Interonset interval, a term in music
Syllable onset, a term in phonetics and phonology
The Onset, Liverpool indie rock group formed by Mike Badger of the Las
The Onset (album), a 2005 album by the band
USS Onset (SP-1224), a United States Navy patrol boat in commission from 1917 to 1918
"Onset", a 2019 song by Haiku Hands

See also
Offset (disambiguation)