SUMMARY: INTRODUCTION: Estrogen receptor expression is lower in breast carcinoma of women ≤45 years compared to women ≥65 years of age, which may imply a higher frequency of basal-like breast carcinomas in younger women. This study evaluated whether there is any difference in the frequency of basal-like phenotype and estrogen receptor (ER)-/HER2- invasive breast carcinomas between women of these 2 different age groups. PATIENTS AND METHODS: A total of 151 women aged ≤45 years or ≥65 years with invasive breast carcinomas were evaluated using tissue microarray, and classified into the following phenotypes: luminal A (ER+/HER2-), luminal B (ER+/HER2+), HER2 overexpression (ER-/HER2+), and basal-like (ER-/HER2- and expressing at least 1 of the basal markers p63, CK5 and/or P-cadherin). RESULTS: ER-/HER2- carcinomas were twice as frequent in women aged ≤45 years (p = 0.0247). However, when the basal-like phenotype was compared with all the other phenotypes grouped together, no statistically significant difference was found (p = 0.0854). CONCLUSIONS: ER-/HER2- carcinomas were more frequent in younger women compared to all the other phenotypes grouped together. An international consensus will be necessary to establish which markers should be used to define basal-like phenotype.