Our aim was to assess whether expression of Foxp3, a marker of Tregs, and IDO were linked with nodal metastasis in breast cancer patients. Foxp3 and IDO using immunohistochemistry. Positively stained cells were quantified and their distribution within the SLN noted. Results The proportion of Foxp3+ cells was higher in SLN of cancer patients than controls (19% v. 10%, p 0.001). Specifically, there were more Foxp3+ cells in SLN with metastasis than tumor-free SLN (20% v. 14%, p = 0.02). The proportion IDO+ cell in SLN of cancer patients was not statistically different than controls (4.0% v. 1.6%, p = 0.08). In order to demonstrate the combined immunosuppressive effect of Foxp3 and IDO, we categorized each SLN as positive or negative for Foxp3 and IDO. The Foxp3+/IDO+ group almost exclusively consisted of cancer patients with node positive disease. Conclusion In conclusion, our study shows that Foxp3+ cells are associated with more advanced disease in breast cancer, a finding that is proving to be true in many other cancers. As IDO has been found to promote differentiation of Tregs, IDO may become a suitable target to abrogate the development of T-cell tolerance and to promote an effective immune response to breast cancer. Our results about the combined expression of IDO and Foxp3 in metastastic SLN support this assumption. Background By the time cancer is clinically detectable tumors have likely developed mechanisms to escape immunosurveillance, and increasing evidence suggests that regulatory T-cells (Tregs) have a major role in modulating host response to tumor. Tregs are produced in the thymus and they act in the periphery to control potentially hazardous self-reactive effector cells that have escaped thymic negative selection. The exact mechanism of suppression is not yet determined; however, Chlorothricin direct cellular contact is required. Regardless, it has been shown that accumulation of Tregs in tumor, as measured by Foxp3 expression, has been associated with a worse prognosis in patients with ovarian cancer[2,3]. In esophageal and gastric cancers higher populations of tumor infiltrating Tregs were associated with more advance disease. Further evidence for the role of Tregs in tumor-specific immunosuppression is seen in murine models where depletion of Tregs promotes an effective antitumor response. Indolamine 2,3-dioxygenase (IDO) is a tryptophan Chlorothricin degrading-enzyme that inhibits T-cell proliferation. IDO is expressed by trophoblasts, dendritic cells and macrophages. IDO has been found to prevent fetal rejection, and it is suspected that it may promote tolerance to tumors. There is evidence that Chlorothricin there is increased expression of IDO in the primary tumor and serum of patients with breast cancer, and that higher levels of IDO expression in colorectal carcinoma represent a poor prognostic factor. Additionally, expression of IDO by leukemic cells in acute myeloid leukemia has been shown to induce Foxp3+ Tregs. The role of IDO has been considered relevant enough that inhibitors of IDO are being developed for clinical trials. These inhibitors could potentially demonstrate utility in breast cancer if IDO promotes progression of disease. Metastasis to lymph nodes is one of the strongest predictors of survival in patients with breast cancer [14-16]. Axillary clearance for lymph node evaluation has been replaced by sentinel lymph node biopsy at many centers in the setting of the appropriate clinical stage. Improved selectivity in lymph node dissection has resulted in a more detailed analysis of the removed nodes, and greater attention is being SDF-5 paid to the immune status of these nodes. Sentinel lymph nodes (SLN) are unique in that they represent both the sites of T-cell activation and early metastasis. As such, these nodes are ideal for investigations of tumor immunology in breast cancer. Recent reports have shown that the immune systems of patients with breast cancer are dysfunctional. Therefore, we set out to find evidence of immunosuppression in the SLN of patients with breast Chlorothricin cancer. We hypothesized that the expression of Foxp3 and IDO within SLN were associated with nodal metastasis. Methods We used SLN of 47 breast cancer patients treated at the Breast Surgery Unit of Helsinki University Hospital between 2001 and 2003. A prospectively collected database was searched to select patients with node negative disease as well as micro- and macro-metastasis. Another criterion was to include patients that also had non-SLN harvested. These patients had either tumor negative SLN (n = 11), SLN with micrometastases (n = 16), or SLN with macrometastases (n = 20) as defined by the.