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Purpose: The h4 integrin has been implicated in functions associated with the genesis and progression of carcinomas based on data obtained from cell lines and mouse models. Data on its expression and relevance to human carcinomas, however, are relatively scant. The aim of this study was to assess its expression and prognostic significance in human breast carcinomas. Experimental Design: We integrated data on h4 expression from multiple gene profiling studies of breast tumors of known clinical outcome with immunohistochemical analysis of 105 breast carcinomas, and we identified genes whose expression correlates with that of h4. Results: The expression of both h4 mRNA and protein is not homogeneous in breast cancer and it associates most significantly with the ''basal-like'' subtype of breast tumors (P = 0.008). No association between h4 and HER2 expression was evident from either gene profiling or immunohistochemical analysis. To gain insight into the relevance of h4 expression to human breast carcinomas, we generated a 65-gene ''h4 signature'' based on integration of four published gene profiling studies that included the top 0.1% of genes that correlated with h4, either positively or negatively. This h4 signature predicted decreased time to tumor recurrence and survival of patients when applied to four data sets including two independent ones. Conclusions: These observations indicate that h4 expression in human breast cancer is restricted and associated with basal-like cancers, and they support the hypothesis that h4 may function in concert with a discrete set of proteins to facilitate the aggressive behavior of a subset of tumors.