There is increasing evidence that tumors elicit specific T‐cell responses in a substantial proportion of patients. Recently, we have shown that in patients with colorectal cancer specific T cells against the tumor‐associated antigens (TAA) Ep‐CAM, her‐2/neu or CEA can be detected in peripheral blood using IFNγ‐ELISPOT assay. In our study, we have analyzed T‐cell responses against HLA‐A*0201‐restricted epitopes of these TAA in peripheral blood of patients with breast cancer and colorectal cancer. Surprisingly, a complete absence of ex vivo T‐cell responses against these TAA was found in 20 patients with breast cancer. In contrast, specific T cells were detectable in 12 of 49 patients with colorectal cancer against at least 1 of these TAA, confirming our previous results. T‐cell responses against influenza‐derived peptides were similar in both malignancies. The results of our study indicate a difference either of tumor immunogenicity or of the migratory pattern of tumor‐specific T cells between breast cancer and colorectal cancer patients. The findings reported here have implications for the development of antigen‐specific T‐cell therapies. © 2003 Wiley‐Liss, Inc.