Scientists have identified a large number of cancer-associated antigens, many of which are now being used to perform cancer treatment vaccines both in basic research and in clinical trials. The list of candidate tumor antigens grows daily, largely because of expanding genetic technology including human genome sequencing and gene-expression profiling. Tumor antigens have been classified into two broad categories: tumor-specific shared antigens and tumorspecific unique antigens [15] . Shared antigens or tumorassociated antigens (TAAs) are expressed by more than one type of tumor cells. A number of TAA are also expressed on normal tissues, albeit in different amounts. As reported in the official National Cancer Institute website (NCI, http://www.cancer.gov/), representative examples of such shared antigens are the cancer-testis antigens [14] , human epidermal growth factor receptor 2 (HER2)/neu protein (reviewed in [16] ), and carcinoembryonic antigen (CEA) [17] . Unique tumor antigens result from mutations induced through physical or chemical carcinogens; they are therefore expressed only by individual tumors. Tumor-specific unique antigens encompass melanocyte/melanoma differentiation antigens, such as tyrosinase [18] , MART1 [19] and gp100 [20] , prostate-specific antigen (PSA) (reviewed in [21] ) and Idiotype (Id) antibodies [11] . Optimally designed cancer vaccines should combine the best tumor antigens with the most effective immunotherapy agents and delivery strategies to achieve positive clinical results. An important dilemma for vaccination against overexpressed tumor-associated antigens is how to induce effective immunity against the chosen target without leading to damaging autoimmunity. The precision offered by DNA vaccines will induce focused immunity against selected antigens, and, as they become more powerful, targets will have to be selected carefully to avoid autoimmunity. Recently, an NCI pilot prioritization study produced a well-vetted, priority-ranked list of cancer antigens [22] . Antigen prioritization involved developing a list of "ideal" cancer antigen criteria/characteristics and assigning relative weights to those criteria using pairwise comparisons. The result of criteria weighting was as follows: (a) therapeutic function, (b) immunogenicity, (c) role of the antigen in oncogenicity, (d) specificity, (e) expression level and percent of antigen-positive cells, (f) stem cell expression, (g) number of patients with antigen-positive cancers, (h) number of antigenic epitopes, and (i) cellular location of antigen expression [22] . Such an effort to prioritize cancer antigens represents the logical next step in attempting to focus translational efforts on cancer vaccine regimens with the highest potential for success.