Please tell me how life threatening is markel cell carcinoma?

Deadly: Neglect it and it will kill you by spreading throughout your body. That's the facts. If it has been excised, your chance of a permanent cure depends on the size and depth of extension of the original lesion. Your personal physician can give you this information. I hope things turn out well for you. These are uncommon and you should try to get two pathologists to sign off on the diagnosis.