Triple‐negative breast carcinomas are a heterogeneous entity that differs between young and old patients

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 triple‐negative 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.