What are the problems with the current staging of discontinuous tumour nodules (DTNs) in colorectal carcinoma? Is there a better way?

Abstract

Discontinuous extramural tumour nodules (DTNs) are deposits of metastatic carcinoma in soft tissue not associated with lymph nodes. Although they are established as an adverse prognostic factor in colorectal carcinoma (CRC), under the AJCC eighth edition staging system their presence does not upstage patients who also have lymph node metastases. Counterintuitively, in some situations the presence of lymph node metastases may in effect downstage a patient with DTNs from pN1c to pN1a/b. Therefore, we sought to critically assess the significance of DTNs in a large unselected single institution cohort of patients undergoing surgical resection for CRC. Of 3822 CRC patients undergoing surgical resection from 2005 to 2021, DTNs were present in 686 (18.0%). In univariate (HR=2.687, 95CI 2.355-3.065; p<0.001) and multivariate analysis (HR=1.805, 95CI 1.529-2.132; p<0.001) in a model including age, gender, stage, grade, location, lymph node ratio and apical lymph node status, DTNs were associated with worse overall survival (OS). N1c patients (DTN present but no nodal metastasis) demonstrated worse OS compared to the current pN1a group (p<0.001) and were least different to the current pN2a group (p=0.571). Within the current N1a (p=0.013), N1b (p=0.004) and N2a (p=0.002) groups, patients who also had DTNs had worse OS. DTNs were associated with worse OS for all stage III CRCs combined (p<0.001), and for stage IIIB (p<0.001) and stage IIIC (p=0.007) individually. We conclude that DTNs are an independent adverse prognostic factor that should be considered in the staging system in a way that is additional to (rather than integrated with) the number of involved lymph nodes. We then assess a simple suggestion for how this could be achieved by increasing the overall stage by one group in the presence of DTNs (requiring the creation of a new stage IIID).