Metastatic pancreas tumors from breast cancer are comparatively uncommon and patients with this tumor usually remain asymptomatic during their life. A 55-year-old woman presented with obstructive jaundice following mastectomy for invasive ductal carcinoma. We diagnosed obstructive jaundice due to a pancreatic tumor demonstrated on computed tomography and performed percutaneous transhepatic cholangio-drainage. Although the patient recovered from the jaundice, she had exacerbation of pneumonia from which she died. At autopsy, invasive ductal carcinoma was found in the pancreas tumor. Immunohistochemical staining was performed to confirm whether the pancreatic tumor was primary or secondary. Human milk fat globules 1 and 2 and gross cystic disease fluid protein-15, which characteristically exist in normal breast tissue or breast carcinoma, were expressed both in the primary breast tumor and the pancreatic tumor. In contrast, both the anti-estrogen receptor and anti-progesterone receptor antibodies stained positively in the primary breast cancer; however, neither of them was positive in the metastatic pancreatic tumor. We report a rare case of a patient who presented with obstructive jaundice from a pancreatic tumor metastasizing from breast cancer and in whom immunohistochemical staining using the antibodies unique to the mammary gland was effective for the diagnosis of this secondary tumor.