Are tumor-associated antigens unique to cancerous cells?
Carcinogenic tumor associated antigens correspond to any peptide chain (antigen) which triggers an immune response from the host. This means that they can be found anywhere inside, at the membrane, and outside of the cell: inside the cell (intracellular), at the cellular membrane and exposed to the extracellular environment, or even secreted.

Depending on the oncogene, they can be also eventually be over-expressed (anywhere there are supposed to be, including the membrane of cells).