The pattern of lymph node metastases in microsatellite unstable gastric cancer

Background Microsatellite instability (MSI) is one of the new groups of molecular divisions of gastric cancer (GC). The aim of this study was to investigate the pattern of lymph node metastasis according to MSI status. Methods MSI analysis of 361 GC patients with information about lymph node stations was performed using 5 quasimonomorphic mononucleotide repeats. The metastasis rates for each lymphatic station was analyzed, combined with clinicopathologic characteristics. Stations were divided into compartments 1–3 on the basis of Japanese Classification. A median number (interquartile range, IQR) of 33 (18–50) lymph nodes were removed and analyzed. Results N0 status was observed in 53.7% MSI patients, and in 29.7% microsatellite stable (MSS) (p < 0.001).The median value of involved nodes was 1 in MSI vs. 5 in MSS (p < 0.001). Furthermore, the number of involved node stations was significantly lower in the MSI group (p < 0.001). MSS tumors showed a higher propensity to spread to second and third compartment nodes. In absence of lymphovascular invasion only 3.2% cases demonstrated positive nodes beyond the first compartment. Skip metastases were seen in 6.1% MSS patients and 0% MSI (p = 0.011). No difference in the 10-year cancer related survival among MSI and MSS patients was found, for both those with 1st compartment (p = 0.223) and with 2nd compartment involvement (p = 0.814). Conclusions MSI GC shows a high rate of N0 stage, a lower number of lymph node metastases, and a less extensive spread to lymph node stations than MSS tumors. These data indicate that tailored lymphadenectomy may be investigated for these patients.