The Relation between Microsatellite Instability and the Thymidylate Synthase Expression in Gastric Cancer

PURPOSE: The main target of 5-fluorouracil (5-FU) is thymidylate synthase (TS). A high TS expression has been identified as promoting resistance to 5-FU. For colorectal cancers, the response to 5-FU based adjuvant chemotherapy is different according to the microsatellite instability (MSI) status. The reports on the relationship between MSI and the TS expression in colorectal cancer have been inconsistent. No data is available for gastric cancer regarding the relationship between MSI and the TS expression. Therefore, we studied the relationship between MSI and the TS expression in gastric cancer. MATERIALS AND METHODS: Ninety-nine consecutive patients who underwent radical gastrectomy for gastric cancer from January 2004 to May 2006 at Bundang CHA hospital were studied. MSI was assessed for five markers (BAT25, BAT26, D2S123, D5S346, and D17S250) by PCR and with using an ABI prism 3100 Genetic analyzer. The TS expression was analyzed by immunohistochemistry with using mouse anti-thymidylate synthase monoclonal antibody to the TS 106 clone. RESULTS: Out of the ninety-nine patients, MSS/MSI-L was detected in 92 (92.1%) cases and 7 cases (7.1%) were MSI-H. A negative TS expression was found in 46 (46.5%) cases, a low TS expression was found in 33 (33.3%) and a high TS expression was found in 20 (20.2%). Out of 92 MSS/MSI-L patients, the number of patients with negative, low and high TS expressions were 46 (50%), 30 (32.6%) and 16 (17.4%), respectively. Out of the 7 MSI-H patients, the number of patients with negative, low and high TS expressions were 0 (0%), 3 (42.9%) and 4 (57.1%), respectively. The relationship between MSI-H and a high TS expression was statistically significant. CONCLUSION: Gastric cancer with MSI-H showed higher levels of a TS expression compared to the gastric cancer with MSS/MSI-L.

A Case of the Primary Small Cell Carcinoma of the Pancreas

A 57-year-old man with severe abdominal pain was admitted to our hospital. Chest PA and simple abdominal X-ray revealed no specific findings, but the abdominal-pelvis CT scan showed a 5cm sized multiloculated cystic tumor originating from the pancreatic head and a 3.2cm sized hepatic lesion that was suspected to be a metastic lesion. A radical operation was not able to be performed because of peritoneal metastasis and gastrocolonal infiltration. Only open lymph node biopsy was done and it revealed metastatic small cell carcinoma. Long-acting octreotide and gemcitabine was administered to the patient, but there was no therapeutic response. The tumor grew very rapidly to 26cm in size and the patient died 2 months later from his first hospital day. Necropsy was performed, and the pathologic finding of the resected mass was confirmed to be small cell carcinoma, the same as the result of the previous lymph node biopsy.