The number of lymph nodes is influenced by the MSI phenotype in resected colorectal cancers (CRC): A study in a large monocentric series.

Abstract

3607 Background: The presence of lymph node (LN) metastasis has important prognostic implications in colorectal cancer (CRC). The number of LN assessed by pathologic examination is positively associated with longer survival. The presence of microsatellite instability (MSI) defines a group of CRCs with a favorable prognosis, which may be due to different immune reaction and LN status. Methods: The aim of the study was to compare the number of LN removed from surgical specimens between MSI and MSS (microsatellite stable) CRCs in a large monocentric series. 1,421 consecutive CRCs with curative surgery were included (364 right colon, 448 left colon-sigmoid, 609 rectum). MSI was assessed by MMR proteins immunohistochemistry in all patients, and a mononucleotidic pentaplex PCR in 796 patients. Results: There were 147 (10.3%) MSI CRCs (109 right colon; 21 left colon; 17 rectum/114 hMLH1 neg; 30 hMSH2 neg; 3 hMSH6 neg). The mean LN number was 32.99 ± 17.08 in MSI vs. 26.45 ± 15.31 in MSS CRC (p < 10-5). 97 (66%) MSI CRCs had no LN metastasis (N0) vs. 647 (50.8%) MSS. The mean LN number in N0 CRCs was 34.15 ± 19.3 in MSI vs. 26.43 ± 16.26 in MSS (p = 0.0003); in N1-N2 CRCs, it was 30.72 ± 11.46 in MSI (p = 0.18 vs N0 MSI) vs. 26.50 ± 14.29 in MSS (p = 0.0187 vs. N1-N2 MSI; p = 0.93 vs. N0 MSS). In MSI CRCs, the LN number was higher in hMLH1 neg (34 ± 17.99) vs. MSH2 neg (30 ± 13.58), but this difference was not significant (p = 0.187) and was only observed in N0 cancers (35.88 ± 20.18 in hMLH1 neg vs. 28.8 ± 15.46 in hMSH2 neg; p = 0.09). There was a relation between the LN number and the localization of the tumour, both in MSI and MSS CRCs. Conclusions: Our results show that MSI CRCs have a higher LN number found in their surgical specimen than MSS CRCs, especially in cases without LN metastasis, in right colon tumors, and in hMLH1 neg cases. This may participate to the favorable prognosis of MSI CRCs. No significant financial relationships to disclose.