We report the case of a 60-year-old female with liver dysfunction resulting from diffuse liver metastases, which, atypically, had originated from breast cancer. She responded remarkably well to trastuzumab monotherapy. She was referred to our hospital because of left breast cancer with multiple general lymphadenopathies. She presented with jaundice and liver dysfunction without a space-occupying lesion or a dilatation of the intrahepatic bile duct on computed tomography images. A liver biopsy was done to rule out autoimmune hepatitis, primary biliary cirrhosis, or primary sclerosing cholangitis, and histopathological examination showed adenocarcinoma in the lymph duct of the liver. Both the primary breast cancer and the liver metastases were negative for hormone receptor expression(ER-, PR-), but overexpressed HER2(HercepTest 3+). She was diagnosed as invasive ductal carcinoma(T1N3cM1, Stage IV). We started trastuzumab monotherapy, which improved her jaundice and liver dysfunction, and resulted in a decrease in lymph node size.