Early studies characterizing the keratin (K) profile of various epithelial tissues indicated that breast carcinoma is K7 positive and K20 negative, but not all breast carcinomas show this profile. Triple-negative carcinoma (TNC) has been characterized by negativity for estrogen receptor (ER), progesterone receptor (PgR), and Her2/neu protein. TNC is more likely to metastasize to the viscera and present as a metastatic poorly different carcinoma. In our study, on the basis of immunohistochemical staining of ER, PgR, and Her2/neu, 75 of the 290 patients with invasive breast carcinoma were judged to have TNC. K20 expression was detected in 6 of 75 patients with TNC, and non-TNC was negative in all 215 cases (P = .0003). K7 expression was also detected in 72 of 75 TNC cases. However, non-TNC was negative in 26 of 215 cases, which was significant (P = .0457). An aberrant profile of K was observed in the TNC group, indicating that caution is needed in determining the site of primary tumors using immunohistochemical algorithms. It should be kept in mind that patients with TNC show highly variable K profiles in practical diagnosis.