A Case of Metastatic Rectal Cancer after Surgery for Gastric Cancer: Diagnosis using Loss of Heterozygosity Analysis

A 65-year-old man with gastric cancer underwent distal gastrectomy in November 2001, i. e., radical D2 resection with curability A. Histopathological findings were tub2, type2, mp, ly1, v1, and n0. In October 2003, he suffered melena. Colonoscopy showed a semicircular type2' tumor 6cm from the anal verge. Biopsy results showed moderately differentiated adenocarcinoma that developed more rapidly than expected for primary rectal cancer, suggesting metastatic rectal cancer. Specimens of resected gastric cancer and biopsied rectal cancer tissues compared using loss of heterozygosity (LOH) analysis showed patterns to be consistent between samples, yielding a diagnosis of rectal cancer metastatic after surgery for gastric cancer. In November 2003, further surgery was attempted, but resection was not possible, so colostomy was conducted. Postoperatively, he was treated with TS-1/CDDP chemotherapy and followed up, but died of hepatic failure in September 2004. LOH analysis was very useful in determining whether the cancer was primary or metastatic.