CANCERS

Simple Summary Lymph node (LN) metastasis is an important prognostic factor in colorectal cancer (CRC). We aimed to search for lymphatic vessels (LVs) in the lamina propria of 39 surgically resected in situ CRC, as well as to detect the presence of tumour burden in the regional LNs. We identified the presence of LVs in the mucosa of all tumours (39/39; 100%) using D240 immunostains. LNs were analysed by both H&E and a RT-PCR-based molecular method. All cases were pN0 with H&E, and the molecular assay detected the presence of low amounts of tumour burden in the LNs of 11/39 (28%) cases, with no clinical consequences at 1 to 5 years of follow-up. The amount of tumour burden in LNs has proven to be a prognostic factor. Despite the fact that pTis is considered to have little or no risk of LN metastasis, our results enabled to quantify the amount of tumour burden within LNs, which may help clinical management. Lymph node (LN) metastasis is an important prognostic factor in colorectal cancer (CRC). We aimed to demonstrate the presence of lymphatic vessels (LV) in the mucosa of in-situ (pTis) CRC, and of detectable tumour burden in regional LNs. This is an observational retrospective study of 39 surgically resected in situ CRCs. The number of LVs was evaluated in both pTis and normal mucosa using D2-40 immunostains. All LNs were assessed with both H&E and the One Step Nucleic Acid Amplification (OSNA) assay, and the results were correlated with clinicopathological features. D2-40 immunohistochemisty revealed LVs in the lamina propria of all pTis CRC (100%), being absent in normal mucosa. A median of 16 LNs were freshly dissected per patient, and all cases were pN0 with H&E. Molecular LN analysis with OSNA revealed the presence of low amounts of tumour burden in 11/39 (28%) cases (range 400 to 4270 CK19 mRNA copies/mu L), which had no clinical consequences. This study demonstrates the presence of LVs in the lamina propria in 100% of pTis CRC, as well as the presence of low amounts of tumour burden in regional LNs, only detected by molecular methods. Given the prognostic value of LN tumour burden, its molecular quantification may help a patient's clinical management.