A 45-year-old woman was seen at the hospital because of upper abdominal pain. There was a past history of undergoing modified radical mastectomy for left breast cancer (scirrhous carcinoma, T2N1, StageIIB) in July 2003. The tumor cells were ER-positive, PgR-positive, and HER-2 negative. Adjuvant hormone therapy was discontinued for reasons of her own. The patient complaining of upper abdominal pain was admitted to the hospital with a diagnosis of intestinal obstruction on June 15, 2006. A long intestinal tube was placed and intermittent continuous suction was performed. On the 5^th hospital day, fluoroscopic study through the ileus tube revealed stricture completely encircled the bowel near the subumbilical region. Primary small intestinal tumor or Crohn's disease was thus suggested and partial resection of the small intestine was performed. Histopathological studies showed invasive proliferation of small atypical cells from serosa to mucosal surface that was extremely similar to that of the breast cancer.
To the best of our knowledge, metastasis of breast cancer to the small intestine is so rare that only 20 surgical cases, including this case, have been reported in the Japanese literature. This case is presented here, together with some references.