Negligible Nuclear FOXP3 Expression in Breast Cancer Epithelial Cells Compared With FOXP3-Positive T Cells

The presence of forkhead box protein 3 (FOXP3) in breast cancer cells is a matter of debate. We systematically analyzed expression of FOXP3 in 1574 breast carcinomas using tissue microarray technology. Weak nuclear staining for FOXP3 was detectable in 1% of all breast cancer cases. According to our results, FOXP3 does not play a significant role in breast cancer biology. Background: The presence of forkhead box protein 3 (FOXP3) in breast cancer cells is a matter of debate. We systematically analyzed expression of FOXP3 in 1574 breast carcinomas. Materials and Methods: For nuclear FOXP3 detection in epithelial breast cancer cells, tissue microarray technology was used. In addition, cultured breast cancer cell lines (ZR75-1, MCF7-WH, BT20, T47D, and SKBR3) were tested for FOXP3 expression using real-time polymerase chain reaction and flow cytometry for messenger RNA (mRNA) and protein quantification. Results: We could neither detect any significant levels of mRNA or protein expression of FOXP3 in human breast cancer cell lines, nor in breast cancer specimens. Weak nuclear staining for FOXP3 was detectable in 16 of 1574 breast cancer cases (1%) and was only seen in a small proportion of malignant cells. There was no difference in survival between patients with FOXP3-positive or -negative tumors. Conclusion: FOXP3 does most likely not play a significant role in breast cancer biology, because it is only scarcely expressed in a very small proportion of breast cancer samples.