Inflammatory breast cancer (IBC) is one of the most aggressive forms of breast cancer. We studied the biological characteristics of these tumours by comparing the overexpression of oncogenes ERBB2, MYC, CCND1 and RHOC and TP53 gene mutation rates in IBC with those found in locally advanced and not otherwise specified breast cancers. The prevalence of the TP53 mutation was much higher in IBC than in the two other types of cancer (57% vs 30). Unexpectedly, however, in IBC tumours, histological grade was independent of TP53 status. In addition, ERBB2 overexpression was twice as frequent in inflammatory as in non-inflammatory tumours, whereas the frequencies of MYC, CCND1 and RHOC overexpression did not vary significantly among the three types of breast cancer. These findings suggest that IBC tumours constitute a distinct subset with a specific pathogenesis. Given the importance of TP53 and ERBB2 in the response to treatments, our observations have important therapeutic implications for the clinical management of IBC patients.