Breast cancer is the most common cancer in women worldwide. Studies have shown that the high temperature requirement factor A3 (HtrA3) is involved in important physiological processes including maintenance of mitochondrial homeostasis, cell death, and cell signaling. HtrA3 is reported to be downregulated in several cancers and has been correlated with advancing cancer stage. We performed a retrospective study using our breast cancer tissue bank to investigate whether the expression of HtrA3 correlated with lymphatic metastasis in breast cancer and whether the expression of HtrA3 was correlated with estrogen receptor (ER) and progesterone receptor (PR) expression in breast cancer. Breast cancer tissues from 156 invasive ductal breast cancer patients with or without lymphatic metastasis were collected and the levels of HtrA3 were measured by immunohistochemistry and western blotting. The expression of HtrA3 was lower in breast cancer. In particular, HtrA3 expression in breast cancer with lymphatic metastasis was lower than that in breast cancer without lymphatic metastasis. In breast cancers with no lymphatic metastasis, the expression of HtrA3 was lower in patients with ER- and PR-positive tumors, but when breast cancers with lymphatic metastasis were analyzed, there was no difference in HtrA3 expression between ER- and PR-positive or ER- and PR-negative tumors. These data suggest that the expression of HtrA3 was negatively correlated with lymphatic metastasis in breast cancer but not correlated with ER and PR positivity or negativity. A better understanding of the mechanism of HtrA3 may provide the basis for future development of a novel therapeutic target in breast cancer. ? 2013 International Society of Oncology and BioMarkers (ISOBM).