A 77-year-old woman was admitted to our hospital due to abdominal pain and body weight loss. A palpable mass the size of an infant's head was tender on palpation and identified as an epigastric lesion. Colonoscopic examination revealed stenosis of the transverse colon, although no intraluminal growth of the tumor was found. The histologic findings of the biopsy material were poorly differentiated and/or undifferentiated cells. Abdominal CT scan showed an irregular-shaped tumor with a diameter of 10cm invading the stomach and jejunum. We performed an operation under a diagnosis of extramurally growing cancer or malignant lymphoma of the colon. Partial resection of the transverse colon was done by distal gastrectomy and partial resection of the jejunum. Histologic examination of the operative specimens revealed moderately differentiated adenocarcinoma of the transverse colon, prominently proliferating into the surrounding tissues. The finding of a long stenotic lesion and extramural compression by colonography are characteristic of this tumor, based on a review of 43 literature reports in Japan.