Tumor endothelial marker 8 (TEM8) is a tumor endothelial-associated antigen that is having an increasingly recognized role in tumor biology. The expression of TEM8 in triple-negative breast cancer (TNBC) has not yet been characterized. We hypothesize that TEM8 is overexpressed in TNBC and in metastatic TNBC in lymph nodes (LN) compared to normal breast tissue and normal lymphatic tissue, respectively. We studied expression of TEM8 in cases of primary (n=17) and metastatic (n=2) TNBC using immunohistochemical analyses. All cases demonstrated increased expression of TEM8 in tumor tissue compared to non-cancerous breast tissue. TEM8 was expressed at a higher level in the stroma adjacent to the TNBC in all cases, with focal immunoreactive areas within the tumor. TEM8 was not expressed in normal lymphoid tissue, but showed expression at sites of LN metastases. TEM8 would appear to represent a new biologic target for designing novel diagnostic or therapeutic approaches for TNBC.