May be shared among several types of tumors.
May be the products of defective or mutated genes unique to a specific tumor.
May be derived from genes only active in early development.
May be silent or minimally expressed.
Can be recognized by T cells.
Activated T cells and antibodies to various tumor associated antigens can be detected in the blood of patients with a number of tumor types, indicating that the immune system has an active role in fighting cancer.