Early gastric cancer metastasizing to the rectum, possibly via a hematogenous route: a case report and review of literature.

BACKGROUND: The most common pattern of recurrence of gastric cancer (GC) is peritoneal dissemination. However, rectal metastasis via hematogenous or lymphatic spread is exceedingly rare. We present a case of a 65-year-old man with an intramucosal GC who developed a rectal recurrence, possibly via a hematogenous route.

CASE PRESENTATION: A 65-year-old man underwent curative endoscopic submucosal dissections for the intramucosal GCs at the anterior wall of the fornix twice. The third GC at the similar location was treated by radical laparoscopic proximal gastrectomy; microscopic examination revealed well-differentiated tubular adenocarcinoma confined to the lamina propria mucosae (T1aN0M0, stage IA). Follow-up colonoscopy revealed a 30-mm submucosal mass in the rectal wall 2 years later, and a metastasis of gastric origin was suspected histopathologically. After a staging laparoscopy confirmed the absence of findings suggestive of serosal involvement or peritoneal dissemination, including negative peritoneal washing cytology, a laparoscopic low anterior resection with lymph node dissection was performed. Microscopically, the tumor was found to mainly be located in the submucosal layer and showed features of moderately differentiated tubular adenocarcinoma. The serosal surface was free of disseminated tumor. Lymph node metastases were identified. Immunohistochemically, there were foci of carcinoma cells that were positive for cytokeratin 20; however, they were negative for cytokeratin 7. Negative staining for caudal-type homeobox 2, a transcription factor indicating goblet cell differentiation, combined with absence of intramucosal carcinoma in the rectal mucosa, suggested a diagnosis of metastatic adenocarcinoma of gastric origin. The absence of evidence of peritoneal dissemination suggested hematogenous or lymphatic spread.

CONCLUSION: Although rectal metastasis from GC, particularly when attributable to hematologic or lymphatic metastasis, is very rare, metastatic gastric adenocarcinoma should be considered as a differential diagnosis for patients who present with a rectal tumor and a past history of GC, even if it is an early GC.