Problem:

I'm learning about antibodies. As I understand it, antibodies detect stranger cells/bacterial/viruses by the molecules present in their membranes. In cancer cells, the cancer cell have produce some unknown protein, so why antibody cannot detect that molecule and kill them?

Required:

Question: Is it that the cancer cell is surrounded by a normal cell?

Question: Is the protein it produces is not obvious in the cell membrane?

Question: Is that the protein can bypass antibody? if so, why?

Explain thoroughly.