OBJECTIVE: To compare the frequency and immunohistochemical profiles of triple-negative breast carcinomas in younger and older women. METHODS AND RESULTS: We selected patients diagnosed with triple-negative breast carcinomas. The groups examined were women who were 35 years old or younger between 1997 and 2007 (n = 74) and, for comparison, women who were 60 years old or older (n = 19, consecutive cases). All formalin-fixed and paraffin-embedded tumor samples were reviewed and immunohistochemically stained for ER, PR, HER2, Ki-67 antigen, epidermal growth factor receptor, cytokeratin 5/6, p53, vimentin, CD117, and p63 using tissue microarrays blocks. Triple-negative breast carcinomas corresponded to 34.6% (74/213) of the carcinomas from the younger patients and 16.2% (19/117) of the carcinomas from the older patients (p = 0.002). No significant differences in the frequency of the basal phenotype were observed in the two patient groups based on CK5/6 and/or epidermal growth factor receptor expression (74.3% vs. 68.4%). However, triple-negative breast carcinomas in the older patients presented a higher frequency of CK5/6 expression compared to those of younger patients (42.1% vs. 9.6%; p = 0.005), whereas triplenegative breast carcinomas of younger patients had a higher expression level of epidermal growth factor receptor (71.6% vs. 47.3%). CONCLUSIONS: These results show that there were significant molecular differences between the triple-negative basal-like breast carcinomas that were diagnosed in younger women and those that were diagnosed in older women. These findings may provide a basis for describing the more aggressive phenotype of the triple-negative breast carcinomas observed in younger women.