Y-box-binding protein 1 (YB1) in breast carcinomas: relation to aggressive tumor phenotype and identification of patients at high risk for relapse.

Aims: To investigate the expression pattern of Y-box-binding protein 1 (YB1) in breast carcinomas, its clinicopathological and prognostic value, and its association with the breast cancer stem cell phenotype [CD44(+)/CD24(-/low)].

Methods And Results: Immunohistochemistry was performed on 225 paraffin embedded specimens of invasive breast carcinomas to detect the expression of the proteins YB1, ER, PR, HER2, p53, Ki67, bcl-2, CD44 and CD24. YB1 protein was detected in the nuclei, the cytoplasm and the stroma of the tumor cells. Cytoplasmic YB1 was detected more often in carcinomas of ductal type (p = 0.002), of higher nuclear grade (p < 0.001), with lack of ER expression (p = 0.002), positive expression of p53 and Ki67 (p = 0.002 and p = 022, respectively), and with present CD44(+)/CD24(-/low) breast cancer stem cells (p = 0.001), while its association with bcl-2 was found to be inverse (p = 0.042). Nuclear YB1 was found to exert unfavorable impact on the disease-free survival of the unselected patients (p = 0.05) and the patients having been subjected to adjuvant chemotherapy and radiotherapy (p = 0.036 and p = 0.05, respectively).

Conclusions: Cytoplasmic YB1 is associated with an aggressive and "stem cell-like" tumor phenotype, while nuclear localization discriminates patients at high risk for recurrence, especially those who are subjected to chemo- and radiotherapy.